A Numerical Simulation-Based Adaptation of the Pedestrian-Level Wind Environment in Village Streets: A Case Study on the Chuan Dao Area of the Hanjiang River in Southern Shaanxi

Abstract

Village streets are indispensable spaces for people to perform outdoor activities, and they also directly affect the outdoor wind environment in villages. At present, people are paying more attention to the wind environment comfort of urban residential areas and urban commercial streets, but there is a lack of attention and research on the wind environment comfort of village and town streets. By summarizing the field research and meteorological data of Lefeng Village, we propose the outdoor wind environment evaluation requirements applicable to the Hanjiang River’s Chuan Dao area in the winter and summer seasons. We found that more than 80% of the outdoor wind environment in the summer is less than 1 m/s. Based on the numerical simulation method of computational fluid dynamics, and on the basis of the characteristics of the streets and lanes in the Hanjiang River’s Chuan Dao area, we found that the wind environment is poor in the winter and summer seasons; regarding streets and lanes, we propose three appropriate values, namely building density, building height, and street width. It is suggested that it is appropriate for the building density of the area to be less than 36%, the height of the building to be less than 15 m, and the width of the street to be 6–11 m when the street is open to traffic and 3–6 m when only pedestrians are passing through the area.

1. Introduction

1.1. Backgrounds

The wind environment is one of the important indicators of green building, as the overall wind environment of the village can directly affect buildings’ energy consumption [1]. Effectively preventing cold wind from invading a large number of villages and towns in the winter can greatly improve the outdoor temperature in the winter, and good natural ventilation in the summer can take away more heat, thus reducing the temperature. If a building is in a village with a good wind environment, the building energy consumption can be effectively decreased, thus reducing the overall energy consumption of the village [2,3] and achieving the goal of sustainable development [4,5]. In order to enhance the village’s habitat, the thermal comfort of indoor and outdoor environments has become a focus of attention for both the state and the people, as it is understood that the outdoor wind environment directly affects the thermal comfort of the human body. Street space, as an indispensable space for human use and activities outdoors, directly affects the indoor wind environment [6]. Therefore, the comfort of the wind environment in the street space directly affects thermal comfort, and the comfort of the street wind environment has a positive impact on people’s quality of life [7]. Qualified street wind environments, especially comfortable wind environments at the height of pedestrians [8], can provide people with a good outdoor space, increase people’s motivation to perform outdoor activities and fitness, and provide a comfortable platform for people’s healthy development.

The research object of this study is located using China’s climate zoning and geographic characteristics of uniqueness in both the hot summer and cold winter regions, where cold regions in the junctions of similar regions in China are very wide across the longitude division range. Moreover, due to China’s many mountains and rivers, it is easy to form a two-mountains-caught-in-a-river geomorphology in Chuan Dao and therefore obtain a wider range of applications. This paper takes the Hanjiang River’s Chuan Dao area in Southern Shaanxi Province (Figure 1) as the object of the study, from which it selects suitable design practices and excludes unsuitable ones. It provides a scientifically valuable design basis for new residential buildings in the area and suggests climate-appropriate improvement strategies for problems that arise.

1.2. Literature Review

The wind environment problem accompanies the formation of cities, and cities all over the world have encountered the street space wind environment problem. Due to the relatively fast economic development and accelerated urbanization in foreign countries, the wind environment problem is highlighted, making it a hot issue researched by many scholars [9]. Scholars in Japan, the United States, and some countries in Europe have previously conducted research on the wind environment. By summarizing and analyzing the climate change in Japan over the past hundred years, these scholars also compared the urban land use changes over the corresponding time scale [10]. Other scholars have found that due to rapid urban development, buildings have gradually become taller and denser, resulting in sea breezes not being able to enter the city smoothly, thus affecting the natural ventilation within the city [11,12,13]. Other scholars have revealed the effect of the high-rise residential layout on comfort in hot summer and warm winter areas [14]. By applying numerical simulations of the wind environment, they created an array model containing more than 20 Japanese residential blocks. The relationship between the building density and the wind environment within a neighborhood was explored through wind environment simulations, and it was found that the more land occupied by buildings within a street, the slower the street wind speed [15]. Therefore, these scholars concluded that building density should be emphasized in the design of urban wind environments [16]. Other scholars used wind tunnel experiments in their research to simulate the wind environment with the stadium space as the main object of study, and the measured data were collated and analyzed with the simulation results, showing that the results differed very little [17]. A numerical simulation of the wind environment and the SIMPLE algorithm method were used to study the dispersion of urban pollutants from a building-wide perspective. The aforementioned study was located in a typical Montreal area [18], and the researchers investigated the relationship between building orientation and the wind environment, concluding that when a building faces the windward side, it has a greater impact on the wind and is prone to forming wind shadow areas and vortices. Narrow-channel winds are also easily generated between buildings due to high wind speeds [19]. The urban wind environment is very helpful in mitigating the heat island effect and may have an impact on urban pollution [20,21]. Since then, more and more scholars have started to focus on the improvement of the urban wind environment [22]. Regarding the research conducted in cities, there are also scholars who have divided the study area into several sub-regions to study the dispersion characteristics of air pollutants and the layout optimization of regional heat sources driven by the wind field based on the prevailing wind direction during the heating season [23].

Some other scholars have explored the air circulation of pollutants in the channels formed between buildings by modeling street-facing buildings. They found that the aspect ratio has an effect on pollutant dispersion [24] and that urban wind environments are very helpful in mitigating the heat island effect and may have an impact on urban pollution [25]. Many existing studies have investigated wind environment problems in urban neighborhoods through simulations using CFD numerical simulation software (ANSYS AIM 18.1) [26,27] and natural ventilation on the inside of relatively narrow streets using computational fluid dynamics simulations [28]. Many scholars also use software simulations to study wind comfort and wind environment optimization [29,30]. The wind environment at pedestrian heights in open spaces, such as squares, parks, and built-up areas, was discussed. The study of this topic has deepened the understanding of natural ventilation in urban buildings, providing a wealth of data experience and design lessons. In order to study the effect of wind heat dissipation on urban streets [31], the dominant wind direction and building heights were also modeled [32]. Studying the wind environment at pedestrian heights is a more scientific approach to assessing the wind environment in urban neighborhoods. It has a positive impact by helping to create better habitats and reduce energy consumption [33]. The study of traditional residential wind environments universally involves using numerical simulation software for wind environments [34], simulating residential indoor wind environments for comparison, and summarizing the ventilation experience [35,36]. Some of the streets in the village are in shaded areas due to building shading, which leads to the uneven heating and cooling of the streets and produces heat pressure ventilation, which enhances the ventilation effect of village streets [37]; additionally, it was found that the overall layout of the traditional village presents a reasonable spatial layout [38]. The wind environments of buildings and courtyards were simulated, and a reasonable strategy for adapting to the wind environment was proposed at the level of architectural space [39]. In order to study the effect of wind and heat dissipation on urban streets, researchers studied the height of the building and the width of the street and altered the aspect ratio of the street [40]. Others have also measured and simulated the wind environment of traditional rural streets in southern Shaanxi and proposed a series of spatial aspect ratios suitable for traditional streets in the region [41]. Others have also studied the wind penetration of low-rise residential buildings through simulation and quantitatively analyzed them through CFD [42]. There are also scholars who have studied the impact on street wind comfort in terms of building form, with authors examining various spatial–functional layouts and testing how these different design approaches affect pedestrian comfort under shell structures [43].

From the above existing studies, it can be seen that most scholars at home and abroad are concerned with urban commercial streets or the inner part of the urban residential area, and there is relatively less research on villages and towns, but at this stage, the country is vigorously developing the construction of the countryside, and the number of people who visit the villages and towns from the city to spend their holidays has also increased. Therefore, this study focuses on the street spaces of villages and towns and conducts research spanning from the overall level of villages and towns to the micro level. Based on the experiences of scholars at home and abroad regarding wind environment research, the wind environment of the village and town street spaces of Hanjiang River Chuan Dao has been studied more scientifically, and the main research problems of this paper include two aspects: the street layout and street space. The single influencing factors affecting the wind environment of the street are studied in depth to discover the wind environment problems existing at the present stage, and the overall comfort of the wind environment is evaluated to find appropriate street and building data for the area so as to encourage future research on the wind environment. Architectural data are obtained in order to achieve the future optimization of the wind environment in the street spaces of townships or villages and towns with common characteristics in the Hanjiang River Chuan Dao in Southern Shaanxi; at the same time, this study explores the significance of the sustainable development of the village and township street planning in the region.

2. Materials and Methods

2.1. Case Overview

2.1.1. Study Area

The study area is located in the Hanzhong region of Shaanxi Province, China, which is situated in the southern part of Shaanxi Province, with the Qinling Mountains in the north and the Micang Mountains in the south and the Hanjiang River flowing from west to east. This study area is typical of the Hanjiang River Chuan Dao area due to its terrain being characterized by the “Two Mountain and Hanjiang folder” (Figure 1). The topography of the Hanjiang River area is flat, and the traditional villages in the Hanjiang River area are mostly distributed in the gentle terrain on both sides of the river or hillside [44]. The distribution of villages is inextricably linked to the climatic conditions, natural resources, and other factors of the area. The topographic and climatic characteristics of the study area are very special [45].

2.1.2. Climatic Characteristics

Currently, there are five typical seasonal division methods in common use. The meteorological division method is mainly used for the selection of meteorological data. Regarding the meteorological division method, in the meteorological department, the period from June to August is usually regarded as the summer season, and the period from December to February of the following year is the winter season. For the statistical method of analyzing meteorological data in the region, the first choice is the typical meteorological year (TMY) data currently used by most energy consumption simulation software, which was proposed by Sandia Laboratories in the United States in the late 1870s, and the core content was adopted using the Finkelstein–Schafer method for statistics. Twelve months with a typical climate are selected to form a complete “hypothetical” meteorological year, and the typical month is the average value of the month in the past 30 years (Figure 2). The FS method is used to measure the similarity between the distribution of the cumulative function of the selected month and the distribution of the long-term cumulative function of the 30-year period.

Based on the existing simulations of outdoor wind environments for buildings, the basic meteorological data source utilized is the “building energy-saving meteorological parameter standards”. In addition, we refer to the method of Zhuangzhi from Tongji University. This author chose Shanghai as the object of study and analyzed the wind environment simulation with dominant wind parameters from 11 local meteorological stations with data from the past 10 years. The recommended methods include the annual average method, the waiting temperature method, the wind frequency maximum method, and the method of using 10 years of meteorological data. The meteorological dataset includes measured data from 270 ground-based meteorological stations in China from 1971 to 2003, and it was applied to the Tsinghua University and China Meteorological Administration (CSWD). The meteorological station located in Hanzhong in the Chuan Dao region of the Hanjiang River was selected to generate year-round and winter–summer wind rose diagrams using Ecotect software (Analysis 2011). The frequency of the wind direction appeared more often in the eastward and westward directions throughout the year, with a higher westerly wind frequency in winter and more easterly wind in summer. Using historical meteorological data from the China Meteorological Network website (https://www.cma.gov.cn, accessed on 15 April 2022), the meteorological station located in Hanzhong in the Chuan Dao region of the Hanjiang River was selected, and the obtained wind data were imported into Ecotect software to generate the annual and winter–summer wind rose diagrams. The wind speed data were counted for the coldest three months in winter and the hottest three months in summer, and the average wind speed was calculated as the basic data in the actual measurement and simulation.

The meteorological data of the area over the past 3 years were also counted to further determine the wind direction and wind speed (Figure 2). For example, Figure 2a,b show the proportions of different wind directions in each month of the winter and summer seasons, where the north and west winds account for a larger proportion of the winds occurring in each month of the winter season and the east and south winds account for a larger proportion of the winds occurring in the summer season. The dominant wind direction in winter in the Hanjiang River’s Chun Dao area in Southern Shaanxi is the range from north to west with a frequency of 58.3%; the wind direction is mostly westerly with a frequency of 32%, and the frequency of static wind is 5%. The average wind speed in winter is 3.46 m per second, and there is mostly northwest wind in winter months due to the influence of the Hanjiang River’s Chuan Dao area; the dominant wind direction in summer is the direction from southwest to south with a frequency of 60%, followed by easterly wind with a frequency of 30%, and the frequency of static wind is 3%. The average wind speed in summer is 2.87 m per second, and under the influence of the topography of the Hanjiang River, the main wind direction in summer months is east.

2.2. Wind Environment Evaluation Indicators

By organizing and analyzing the evaluation standards of the wind environment at home and abroad [46], combined with the relevant national evaluation standards and the evaluation standards of the wind environment in various studies, it can be seen that various types of wind environment evaluation indexes have certain limitations [47]. Through the comprehensive consideration of the evaluation standards of various types of wind environments, it is proposed to meet the wind environment evaluation standards of the Hanjiang River’s Chuan Dao area. According to the relevant literature from home and abroad, it is known that Yang Qian of the Beijing Architecture University conducts research on the wind environment at pedestrian height in the Beijing Winter Olympic Village, and Fu Jun et al. of the Zhejiang University of Science and Technology conducts research on the wind environment at pedestrian height on the campus; it is explained in the article by Liang Chuanzhi et al. that the wind environment at pedestrian height is an important part of the wind environment around the building. In Liang Chuanzhi et al.’s research, it is also shown that the wind environment at pedestrian height is an important part of the wind environment around the building, and dealing with the wind environment at pedestrian height can help improve the comfort of pedestrians [48]. Therefore, the wind environment at pedestrian height (1.5 m) is mainly evaluated. The wind environment of the Hanjiang River’s Chuan Dao area was comprehensively evaluated by combining the wind speed, wind vortex, wind speed ratio, wind speed amplification factor, and air pollutants based on the street layout and space (

Table 1. Outdoor wind environment evaluation criteria for Hanjiang River’s Chuan Dao area, Shannan, China.

Name	Wind Speed (1.5 m)	Wind Vortex	Wind Speed Ratio	Wind Speed Amplification Factor	Air Pollutant Concentration
winter	V ≤ 5 m/s Comfortable wind environment	Avoid	The greater the wind speed ratio, the better the ventilation effect	<2	When V < 1 m/s, pollutants easily deposit, and the lower the wind speed, the greater the pollutant concentration.
summer	1 m/s ≤ V ≤ 5 m/s Comfortable wind environment				The greater the wind speed, the lower the pollutant concentration.
	V < 1 m/s or V > 5 m/s Uncomfortable wind environment

).

2.3. Questionnaires and Measurements

Questionnaire Survey

The method of using a questionnaire survey is more objective and can help understand the subjective feelings of respondents, which is a common method of scientific investigation. In order to study the current situation of the wind environment in the village and town street spaces in the Hanjiang River’s Chuan Dao area from the user’s point of view, a questionnaire on the subjective feelings about the wind environment in the village and town street spaces in Hanjiang River’s Chuan Dao area was compiled in this study.

The most important part of the questionnaire is the subjective evaluation of the outdoor wind environment by the respondents, which refers to the evaluation of the current outdoor wind environment in village and town street spaces, including the comfort of the wind environment in winter and summer daytime streets, the satisfaction with the wind speed in streets in winter and summer, the satisfaction with the diffusion of pollutants in streets in winter and summer, as well as the general evaluation of the current outdoor wind environment in the streets. This part of the survey in the form of a scale (source: thermal environment ergonomics using a subjective judgment scale to evaluate the impact of the thermal environment, GB/T18977-2003) [17] can provide valid and comparable data on the feelings of the street wind environment; the scale is shown in

Table 2. Outdoor wind environment evaluation criteria for the Hanjiang River’s Chuan Dao area, Shannan, China. In parentheses in the third column are the vacancies that require the respondents to provide a score ranging from −3 to 3 for the associated comfort level.

Evaluation of Outdoor Wind Environment (−3, Very Dissatisfied/−2, Very Dissatisfied/−1, Slightly Dissatisfied/0, Neutral/1, Mostly Satisfied/2, Very Satisfied/3, Very Satisfied)
Street wind environmental comfort	−3   −2   −1   0   1   2   3	winter (  ) summer (  )
Street wind speed satisfaction	−3   −2   −1   0   1   2   3	winter (  ) summer (  )
Pollutant dispersion satisfaction	−3   −2   −1   0   1   2   3	winter (  ) summer (  )
Open space wind environment satisfaction	−3   −2   −1   0   1   2   3	winter (  ) summer (  )

.

2.4. Wind Environment Measurement

A Testo 425 handheld hot-wire anemometer with a measurement accuracy of 0.01 m/s and a measurement error of +5% was used to measure the wind speed at fixed measurement points on site. The height of the measurement point was 1.5 m, mainly chosen around the street space, including the internal streets of the town, street entrances and exits, public activity venues and places where other pedestrian activities frequently take place, and the back sides of buildings and building enclosures where there is a higher degree of a possible adverse wind environment. The main streets and alleys were measured using uppercase English letters, and the secondary streets and alleys were measured using lowercase English letters. The measurement points were divided into four groups (Figure 3). The first group of measurement points included B, C, D, and E; the second group of measurement points included A, G, and F; the third group of measurement points included b, c, and e; and the fourth group of measurement points included a and d. Measurements were carried out using one-point, multiple-measurement, and multipoint-simultaneous-measurement methods, in which each group of measurement points was measured at the same time for one hour, and a set of 60 consecutive readings of the wind velocity were taken with a continuous measurement time of 10 min, and 10 sets of wind velocity data were recorded for each group of individual measurement points. We recorded 10 groups of wind speed and obtained 600 wind speed data points, and the average value of each group of data was summarized.

2.5. CFD Setup and Validation

2.5.1. Software Calculation Parameter Settings

Calculation area: The height of the calculation domain for numerical simulation was 3 times the average height of the building with reference to the numerical simulation of the outdoor wind environment and the provisions of the manual. The width of the calculation domain was centered on the target building, and the radius was 5 times the building height. The calculation domain width was selected using the simulation diameter, D, as the base scale, and the calculation domain width was set to 5 times the diameter of the site.

Grid division: The grid division adopted a hybrid grid, and the grid accuracy was about 1/10 of the building scale (about 0.5–5 m). The grid at the pedestrian height of 1.5 m next to the building was 10 or more, the grid as a whole was dense at the bottom and sparse at the top, and the grid at the channel between the two buildings was set to have more than 10 layers. When setting up the grid division by using the software for simulation, the number of grids increased when the calculation area was too large, which led to an increase in the time and number of calculations. There was a risk of failure of the calculation results, leading to a decrease in the accuracy of the simulation. A reasonable grid division directly affects the results of the simulation.

Combined with the actual situation, the calculation area is determined as follows:

(1)

In the inlet direction, the length is taken as 1 times the length of the village and town;

(2)

In the outlet direction, the length is 3 times the length of the village;

(3)

In the left and right directions, the length is 3 times the length of the village;

(4)

In the left and right directions, the length is 3 times the width of the village and town;

(5)

The height is 5 times the average height of the building in the village or town.

Inlet boundary conditions: Since the object under study has an incompressible flow, the velocity inlet (velocity) provided by FLUENT was used to define the velocity at the inlet boundary of the flow and other scalar type (e.g., temperature) variables of the flow. In order to have a clear idea of the exact extent to which different undercuts affect the magnitude of the wind speed with an increasing height, two mathematical formulas, logarithmic and exponential, were used in wind engineering to describe the problem, though the exponential law is commonly used. In addition to considering the variation in the incoming wind speed with height, in turbulent motion, the turbulent kinetic energy, k, and the turbulent dissipation rate £ are the most important characteristic quantities that characterize the development of turbulence, which vary according to different incoming wind speeds and the height of the ground. The expressions of the turbulence kinetic energy, k, and turbulence dissipation rate £ are given in the Fluent help manual.

Outflow boundary conditions: The outflow boundary conditions provided by FLUENT were used to describe the outlet boundary, where the flow velocity and pressure were unknown before the solution, which was suitable for the case where the flow at the outlet was fully developed. The calculation area was taken as three times the length of the building in the outlet direction, which ensured that the flow was fully developed.

The top and sides of the computational area: The symmetry boundary conditions provided by FLUENT were used for the case where the physical shape and the desired flow solution had mirror symmetry characteristics, where the gradient of the flow rate, temperature, pressure, etc., was equal to zero, and where the same physical phenomena existed on both sides of this boundary.

Building surfaces and floors: The wall boundary conditions (wall) provided by FLUENT were used to confine the fluid and solid regions.

Through understanding the end-flow model in the numerical software simulation, most of the outdoor wind environment simulations used the standard k-ε model, including the software end-flow model selection, the selection of the basic k-epsilon (2 eqn) model, and the choice of the fluid material for the air (air). In the settings of the convergence parameters, the iteration number and step size were obtained. The calculation can be stopped when the solution is sufficiently converged, so it can be determined when the value of the observation point does not change. When the root mean square residual is less than 0.0001, the initial parameter in the software is set to 0.001, so the initial value will be modified by 1 × 10⁻⁴ to determine the convergence of the simulation of the wind environment of the street, and the calculation of the number of iterative steps is set to be modified to 1500 according to the study, and the step size is 1. The basic boundary condition parameters were set as follows: according to the statistical results of the meteorological data shown in Section 2.1.2, the inlet wind speed and wind direction were set, and the inlet wind speed in winter was 3.64 m/s, and the wind direction was westerly; the inlet wind speed in summer was 2.87 m/s, and the wind direction was easterly.

Ground and wall conditions: The ground and wall were set as no slip, and the height of the simulation area was 1.5 m. Neglecting the wind speed of the upper part of the building, only the horizontal wind speed was set, and the wind speed in the normal direction of the ground was zero.

2.5.2. Validation of Simulation Validity

The validation object was chosen to be Lefeng Village in the Shangyuan Guan Township, and the measurement points were chosen as typical measurement points in each group of measurement points in the actual measurement, with B being chosen for the first group of measurement points, G for the second group, e for the third group, and a for the fourth group (Figure 3). The average wind speed at each measurement point was used for comparison with simulated data from the software [49,50,51]. The entrance wind speed was 2.87 m/s, and the wind direction was easterly. The floor and wall were set to be no slip, and the height of the simulation area was at 1.5 m of the pedestrian height. The wind speed of the upper part of the building was neglected, only the horizontal wind speed was set, and the wind speed in the normal direction of the ground was 0.

A comparison of the test data and simulation data of Shangyuan Guanzhen is shown in a line graph in Figure 4, from which it can be seen that the simulated values are larger than the measured values; the reason for this situation may be because of the influence of the surrounding complex environment during the actual measurement process, which may have led to the measured data values being small and the simulation conditions being relatively more idealized, therefore resulting in large values [52,53]. Although the actual measurement can directly reflect the wind environment, it will be affected by external factors, while the software simulation can exclude certain effects and can produce more ideal results. The measured and simulated change rule curves are basically the same; firstly, it can be shown that the software numerical simulation research method is feasible, and the software’s basic calculation boundary conditions, models, grids, and basic parameter settings are more reasonable to ensure the reliability and rationality of the study.

2.5.3. Physical Modelling

Physical model establishment: In the third part, the street space pattern simulation model was established, and through field research, the old town street space pattern in the Hanjiang River’s Chuan Dao area could be divided into three common kinds, namely, “a” shape, “T” shape, and “ten” shape. The local building scale was 15 × 15 m, and most of the main streets had a height-to-width ratio of about 0.5, which was combined with the average building height of about 10 m measured by the actual research, so the building width of the model was set to 15 m, and the street width was set to 20 m; in the spatial index part, the suitable simulation values were also determined through field research. The spatial indicators were also determined through field research to determine the appropriate simulation values. According to the building volume ratio, the maximum building density control index table, and the new rural construction guideline standard, the maximum design building density should not exceed 30%, but the actual research found that the building density in some areas of the village and town was larger, namely more than 30%. Therefore, the ideal model selects the number of building units as 36 (6 × 6), 64 (8 × 8), and 100 (10 × 10) for the three schemes, and the building density of each scheme is 20.25%, 36%, and 56.25%, respectively; according to the technical points of the construction of healthy housing, the net height of the residential building should not be lower than 2.5 m. The “Uniform Standard for Residential Buildings” stipulates that the size of the floor height should be in the range of 2.0 m~3.0 m; the current building heights are high, and most of the buildings have more than 2 floors, so the ideal model selects the average height of the buildings as 6 m, 11 m, and 15 m for the 3 groups. The width of the streets of the ancient towns in the Chuan Dao area of the Hanjiang River is relatively narrow, with the width of the main street generally being around 5 m, the width of a very small number of vehicle-passable streets being about 14 m, and the width of secondary streets generally being 3.5 m. The width of streets with more intensive residential activities is relatively narrow. Therefore, the ideal model chooses the street widths of 3 m, 6 m, and 12 m for the 3 groups. The height of the building model is 6 m, and the height-to-width ratio of the street ranges between 0.5 and 2.

3. Results and Discussion

3.1. Questionnaire and Measurement Results

3.1.1. Questionnaire Results

The number of questionnaires distributed in this study was 300, and 292 were validly returned with a valid usability rate of 97% (Figure 5). Figure 5a shows that in the single item of winter and summer daytime street wind environment comfort, 16% of the respondents think that the winter daytime street wind environment comfort is poor, and 43% of the respondents think that the winter daytime street wind environment comfort is good; 49% of the respondents believe that the summer daytime street wind environment comfort is poor, and 14% of the respondents believe that the summer daytime street wind environment comfort is good. Due to the enclosed layout of the settlement, the enclosure of the internal buildings is higher, resulting in lower wind speeds in internal streets and alleys, causing a difference in the winter and summer monsoon wind comfort, which is perceived as being better in the winter than in the summer.

Figure 5b shows that in the single item of winter and summer daytime street wind speed satisfaction, 31% of the respondents think that the winter daytime street wind speed is poor, and 46% of the respondents believe that the winter street wind speed is better; 50% of the respondents believe that the summer daytime street wind speed is poor, and 18% of the respondents think that the summer daytime street wind speed is better. This includes high satisfaction with wind speeds in the winter and slower wind speeds in the summer, where hot air should not diffuse, which is consistent with the comfort survey results.

Figure 5c shows that in the single item of winter and summer street pollutant dispersion satisfaction, 45% of the respondents perceived the winter daytime street pollutant dispersion to be poor and 28% perceived the winter street pollutant dispersion to be good; 49% of respondents perceived the summer daytime street pollutant dispersion to be poor and 18% perceived the summer daytime street pollutant dispersion to be good. The questionnaire shows low satisfaction regarding the diffusion of pollutants in streets and alleys in the winter and summer, and shows that pollutants are easily deposited in the winter and summer, and the reason why the summer is slightly worse than the winter is that the summer weather is hot and muggy, which leads to an increase in unpleasant odors and therefore worse satisfaction.

Figure 5d shows that in the single item of satisfaction with the wind environment in open spaces in the winter and summer, 22% of the respondents thought that the wind environment in open spaces in the winter was poor, and 47% thought that the wind environment in open spaces in the winter was better; 47% of the respondents thought that the wind environment in open spaces in the summer was poor, and 27% thought that the wind environment in open spaces in the summer was better. There is a large gap between the satisfaction of open space wind environment in the winter and summer. Due to the slow wind speed in the winter, the penetration of cold wind in open spaces is not obvious and is more suitable for activities; in the summer, the wind speed is slow and there is no shade, so the air is stifling and the comfort level is poor.

3.1.2. Wind Speed Measurement Results

Analysis of measured data: The outdoor summer wind speed of Lefeng Village was measured from 8:00 a.m. to 12:00 p.m. The investigation of the China Meteorological Data Network (http://data.cma.cn/ (accessed on 15 April 2022)) was carried out; the station is located in Hanzhong City, Shaanxi Province with the number of 57,127, and the maximum wind speed is known to be 3.1 m/s according to the daily values of the China Ground Climate Data and the observation of the fixed-time values of the China High Altitude Weather Station. The maximum wind speed at 0:00 and 12:00 on 23 July was determined to be 1.68 m/s on average during the test time.

A total of 12 measurement points were obtained simultaneously, and the height of 1.5 m was used. From approximately 8:00 a.m. to 12:30, using every 30 min as an interval, each measurement point was recorded in 10 groups of wind speed data, and each group of measured data will be summarized to take the average to obtain the 10 groups of measurement points at the average wind speed. The results are shown in

Table 3. Summary of wind speed at measuring points in Donghan Village, Shangyuan Guan Township.

Measuring Point	Average Wind Speed	V < 1 m/s	1 m/s ≤ V ≤ 5 m/s	V ≥ 5 m/s
A	0.35	100%	0%	0%
B	0.21	100%	0%	0%
C	0.27	100%	0%	0%
D	0.90	70%	30%	0%
E	0.83	70%	30%	0%
F	0.53	90%	10%	0%
G	0.27	100%	0%	0%
a	0.61	80%	20%	0%
b	0.29	100%	0%	0%
c	0.30	100%	0%	0%
d	0.80	70%	30%	0%
e	0.23	100%	0%	0%

.

The first group of measurement points, including B, C, D, and E (Figure 6a), is located along the highway on the west and east sides of the village, which is the main entrance of the village and has a large flow of people and vehicles. Therefore, in the actual measurement, measurement points B and C are on the windward side of the prevailing wind in the summer, with relatively large wind speeds, while the wind speeds on the leeward side of the village at points D and E are smaller, making the environment hot and stuffy and not conducive to ventilation in the summer, and the wind environment is not ideal. In the first set of measurement data, the average wind speed exceeds 1 m/s in 7 out of 10 data measurements at each measurement point, and the probability of the average wind speed exceeding 1 m/s at measurement points B and C was 0%. Measurement points D and E have a 35% probability of having an average wind speed greater than 1 m/s, which tends to cause discomfort in the summer (Table 3).

The second group of measurement points, including A, G, and F (Figure 6b), is located along the main street and alley, respectively, at the entrance, exit, and center of the main street, which is the main road of the village and is surrounded by stores with a large flow of people; according to the observations, the residents and tourists from the main entrance pass through the entrance plaque building and enter the main street of the village to visit, and there is almost no greenery on the two sides of the main street and alley. The spatial direction of the main street develops towards various angles, connecting various houses and buildings in the village, and at the same time, it serves to connect internal transportation and increase accessibility. Measurement point A is located at the entrance of the ancient town, including the entrance into the pagoda; both the east and west sides of the stores do not have tall buildings blocking the site, making it relatively open, resulting in the huge flow of people. Measurement point G is located in the middle of the main street of Lefeng Village, Shangyuan Guan Township. As the second group of measurement points is located in the village streets and alleys, the average wind speed of measurement points A, G, and F is basically less than 1 m/s, and only 5% of the average wind speed of measurement point F is greater than 1 m/s, and this street has almost no greenery, making it easy for pollutants to be deposited in the summer and making it stuffy, resulting in a poor wind environment (Table 3).

The third group of measurement points includes b, c, and e (Figure 6c) and is located in the secondary streets of the ancient town, and the secondary alleys are the main transportation streets within Lefeng Village, Shangyuan Guan Township. From the profiles of different locations, the main entrances of the buildings on both sides of the street are generally set up on the street. It can be seen that the relationship between the buildings and the street is relatively close, the average wind speed is less than 1 m/s at each measurement point, and the average wind speed is less than 0.5 m/s at measurement points b and c. In the winter, the wind mainly comes from the west and northwest, and the density of the buildings and the many alleys prevent the wind from the east from entering the area. The measured data show that the ventilation effect of this group is poor (Table 3).

Measurement points a and d (Figure 6d) of the fourth group are located in the square and public activity site of Lefeng Village in Shangyuan Guan Township, respectively. Only 10% of the average wind speed at measurement point a is greater than 1 m/s, while those of the rest of the measurement points are less than 1 m/s, and the probability that the wind speed at measurement point d is greater than 1 m/s is 15%. In the summer, the wind mainly comes from the east, but the density of buildings and the many alleys prevent the wind from the east from entering the plaza and the public activity sites (Table 3).

The measurement of the average wind speed at each measurement point shows that the wind conditions at each measurement point are very complex. The wind speed varies from point to point with great differences. According to the relative comfort evaluation criteria, wind speeds in the range of 1.6 to 3.3 m/s are considered comfortable (Table 2).

3.2. The Results of the Simulation Evaluation of the Overall Layout of Lok Fung Village

According to the evaluation criteria, the overall layout of the streets and alleys in Le Feng Village, Shang Yuan Guan Township is a regular mesh, and the overall wind environment is more uniformly distributed; the direction of prevailing winds in the winter and summer is blocked by buildings, but the entrances of the streets and alleys are parallel to the direction of the dominant winds, which leads to faster wind speeds flowing into the streets and alleys and slower wind speeds perpendicular to the dominant winds in the streets. The average wind speed in the winter is 2.18 m/s, which can satisfy the requirements of wind comfort and makes it easy for the pollutants of the streets to be deposited with slower wind speeds. The formation of dust causes poor air quality in the street. The average wind speed in the summer is 0.59 m/s, which is much lower than that in winter, and the range of wind speed v < 1 m/s is larger, while the wind speed in the street is slow, so the overall wind comfort requirements are not met in the summer (

Table 4. Environmental evaluation of pedestrian height winds in village and town street layouts in Hanjiang River’s Chuan Dao area, Southern Shaanxi Province, China, where a “√” indicates compliance and cross indicates “×”.

Name	Seasonality	Comfortable Wind Speed	Wind Vortex	Wind Speed Ratio	Air Pollutant Concentrations	Wind Pressure Difference
Lefeng Village, Shangyuan Guan Township	Winter	√	√	0.60	√	<5 pa
	Summer	×	√	0.33	×	--

) (Figure 7).

An evaluation of the wind environment at pedestrian height in relation to the street layout of the village and town in the Hanjiang River’s Chuan Dao area in Southern Shaanxi Province is carried out, and the results are shown below.

(1)

Evaluation based on comfortable wind speed

The wind speed at pedestrian height in the streets and alleys under the dominant wind direction in the winter in the Lafeng Village of the Shangyuan Guan Township is relatively slow, and the wind speed in the winter can basically reach the comfort standard; the wind speed at pedestrian height in the streets and alleys under the dominant wind direction in the summer is relatively slow, and the wind speed in the summer in the Lafeng Village of the Shangyuan Guan Township cannot reach the comfort standard. The reason is the difference caused by the width of the street entrance, orientation, and building density. The street entrance is open and unobstructed, which is favorable for airflow; the density and layout of street and alley buildings will affect the airflow and wind environment comfort (Figure 7a(1,2),b(1,2)).

(2)

Evaluation based on wind vortex

The wind vortex situation in Lefeng Village in the Shangyuan Guan Township is better due to the grid-like and more regular layout, which leads to a higher degree of enclosure in the streets, which is not suitable for generating a larger wind vortex area, and a more open space is prone to generating a larger wind vortex area. The scattered layout of buildings and unreasonable arrangement of plazas and other activities of long land will lead to chaotic air flow and affect the comfort of the wind environment (Figure 7a(1,2),b(1,2)).

(3)

Evaluation based on wind speed ratio

It can be concluded from Table 4 that the wind speed ratio is small, proving that the ventilation effect is poor, mainly due to the aspects of the street width and street building density; differences in the winter and summer in Lefeng Village, Shangyuan Guan Township are mainly present because there is a building block on the dominant wind direction in the summer, and it is not suitable for the air to flow into the interior of the ancient town, resulting in a slower wind speed.

(4)

Evaluation based on air pollutant concentration

In Table 4, it can be seen that the ventilation effect of Lefeng Village in the Shangyuan Guan Township is poor in the winter and summer, and the air quality is relatively low, which is related to the influence of a comfortable wind speed and the wind speed ratio. Therefore, the air quality inside the colony is poor.

(5)

Wind pressure difference

The wind pressure difference in Lefeng Village, Shangyuan Guan Township is within a reasonable range, and the reason why the wind pressure difference is less than 5 pa is that the windward surface area is large and there are dense buildings directly blocking it, so the internal wind pressure does not change much, and therefore, it is not possible to form good natural ventilation, which leads to poor air circulation (Figure 7a(3),b(3)).

3.3. Results of Street Crossing from Simulation Evaluation

By observing the simulation results of the three different spatial layout models for streets in Group A, it can be seen from the wind speed cloud and wind speed vector diagrams that at pedestrian height (1.5 m), when the dominant wind is blowing from due west, the main windward side is different for different street layouts, and therefore, the wind speed and wind vortex situation in the wind shadow area of the interior of the street and the leeward side of the street building are both different. The wind speed in the wind shadow area on the leeward side of the street and the street building will change with the change in the layout. The wind speeds of the smooth wind paths inside the “I”-, “T”-, and “X”-shaped streets and alleys are the same, but the wind speeds will change when there are intersecting streets and alleys, and the wind speeds of the wind shadow zones and wind vortices in the wind shadow zones of the three layout methods are different. The scope of the wind shadow area and the area of vortex wind in the wind shadow area increase; in turn, the wind shadow area behind the building of the “T”-shaped and “X”-shaped streets and alleys is larger, and the degree of wind dispersion is larger in this area, and at the same time, there will be a stagnant point in the back of the building, so the wind speed in this area is the lowest. Parallel to the incoming wind direction of the “I”-shaped streets and alleys, the airflow is smooth, and the flow rate is stable. In the “T”-shaped and “X”-shaped streets, the wind speed in the vertical direction decreases very significantly. Among them, the wind environment of the “X”-shaped streets is the most cluttered (

Table 5. Indicators related to wind speed for different street crossing forms.

Name	Range of Wind Speeds in Streets and Alleys	Maximum Wind Speed	Average Wind Speed	Wind Speed Range in Wind Shadow Area	Wind Speed Ratio
(a)	1.48 m/s~2.92 m/s	2.92 m/s	2.20 m/s	0.03 m/s~0.83 m/s	0.60
(b)	2.22 m/s~3.62 m/s	3.62 m/s	2.92 m/s	0.20 m/s~1.20 m/s	0.80
(c)	1.76 m/s~3.31 m/s	3.31 m/s	2.54 m/s	0.02 m/s~0.60 m/s	0.70

).

(1)

Evaluation of wind environment of cross form of “I”-shaped streets and alleys

Through a simulation combined with the outdoor wind environment evaluation proposed in the previous section, when the street space is in the form of “I”, the air circulation in the street is smooth, the wind speed is faster, and it is not suitable to produce vortices in the street, which is conducive to the improvement in air quality, making the wind environment comfortable in the winter and summer. At the same time, it should be noted that to optimize the dominant wind direction in the winter, the street should not be set up in an “I” shape; it can be adjusted through the street direction or by planting vegetation to obtain the effect of wind protection. In the summer, the dominant wind direction should be optimized through an “I”-shaped street, which will be conducive to ventilation in the villages’ and towns’ internal streets and alleys (Figure 8a).

(2)

Evaluation of wind environment of “T”-shaped street crossings

Through a simulation, combined with the outdoor wind environment evaluation proposed in the previous section, when the street space is “T”-shaped, when the wind reaches the corner of the street, the airflow changes, and the airflow speed in the street decreases, while the wind shadow area on the back of the building increases, generating a wind vortex, and the wind environment is comfortable in the winter and uncomfortable in the summer. Therefore, when there are too many “T”-shaped streets in the street layout, it will make the wind environment worse, and this situation should be solved based on the direction of the street (Figure 8b).

(3)

An evaluation of the wind environment in the form of street crossings in the shape of an “X”

Through a simulation, combined with the outdoor wind environment evaluation proposed in the previous section, when the street space is in the shape of an “X”, the wind environment characteristics are similar to those of a “T”. The wind speed of the street perpendicular to the dominant wind direction is poor, the wind environment is uncomfortable in the summer, and the air quality is poor in the winter and summer (Figure 8c).

3.4. The Results of the Evaluation of Spatial Indicators for Streets and Alleys

By observing the simulation results of the three models with different street building densities, it can be concluded from the wind speed cloud and wind speed vector diagrams that the wind speed and wind vortex conditions are different in the interior of streets with different building densities and in the wind shadow area on the leeward side of the street buildings when the dominant winds are blowing from due west at pedestrian height (at 1.5 m). Changes in building density lead to differences in the wind environment in the internal alley space of the buildings, with the internal air circulating more easily in the layout in Figure 9(a1), with a building density of 20.25%; Figure 9(a2) shows moderate wind speeds, but with a greater degree of wind dispersion in the internal area; and Figure 9(a3) shows the slowest wind speeds, with almost no wind in the internal alley. The range of the wind shadow area and the area of vortex wind within the wind shadow area of the three building density simulations gradually increase, and the area of the wind shadow area at the rear of the a2 and a3 buildings is larger, with a greater degree of wind discretization in the area, while a wind stagnation point will also be generated at the rear of the building, which has the lowest wind speed. Parallel to the incoming wind direction of streets and alleys with low building density, air flows smoothly, and the flow rate is stable. Streets and alleys with medium building density have reduced airflow speeds and are prone to wind vortices and scattered wind fields. The airflow in alleys with the highest density of buildings is too slow, and the wind environment is poor.

By observing the simulation results of the three models with different building heights in streets and alleys, it can be concluded from the wind speed cloud and wind speed vector diagrams that the wind speed and wind vortex conditions inside the alleys with different building heights and in the wind shadow area on the leeward side of the street buildings are different when the dominant winds are blowing from due west at pedestrian height (at 1.5 m). Changes in building height lead to the differences in the wind environment in the internal alley spaces of the buildings. The layout in Figure 9(b1) shows a building height of 6 m, and the internal air flow is relatively slow, and the wind speed change is small; in Figure 9(b2), the wind speed is moderate, but the wind speed of the internal area wind begins to increase; in Figure 9(b3), the internal alley’s wind speed is the largest, as it is relatively strong. In Figure 9(b1),(b2), the internal wind dispersion is relatively high. The range of wind shadow area and the area of vortex wind in the wind shadow area simulated for the three building heights are basically the same, and the airflow in the street alley with low-height buildings parallel to the direction of the incoming wind is smooth with a stable flow velocity. The air flow velocity of the street with middle-height buildings decreases, and the wind vortex easily appears, while the wind field is scattered. The airflow of the street model with the maximum building height is too fast, and the wind environment experience is poor.

By observing the simulation results of the three models with different street widths, it can be concluded from the wind speed cloud and wind speed vector diagrams that the wind speed and wind vortex conditions inside the street with different widths and in the wind shadow area on the leeward side of the street buildings are different when the dominant wind is blowing from due west at pedestrian height (at 1.5 m). The change in the street width leads to differences in the wind environment in the internal alley space of the building. Figure 9(c1) shows a street width of 3 m with a relatively slow internal airflow, and the wind speed change is small; in Figure 9(c2), the wind speed is moderate, but the wind speed of the internal area begins to increase; in Figure 9(c3), the internal alley’s wind speed is the largest, appearing to have relatively strong wind. The scope of the wind shadow area and the area of vortex wind in the wind shadow area of the three building simulations are basically the same, and the airflow in the alleys with low-width buildings parallel to the direction of the incoming wind is smooth, but the flow speed is slow. The airflow rate increases in the streets and alleys with medium-width buildings, and the wind environment situation is more favorable. The widest modeled streets and alleys have excessively fast airflow and a poorer wind environment experience.

(1)

Building density

Through the simulation combined with the outdoor wind environment evaluation standard of Hanjiang River’s Chuan Dao area in Southern Shaanxi Province, it can be concluded based on Figure 10a that the building density is negatively correlated with the wind speed, and the higher the building density, the lower the wind speed in the street. When the building density is less than 36%, the street wind environment can meet the outdoor wind environment evaluation standards. When the building density continues to increase, the building density reaches 56.25%, the wind speed inside the street will be reduced, and there is a static wind area, which is not conducive to summer ventilation, and at the same time, the pollutants inside the street are easily be deposited. Therefore, it is appropriate to combine the relevant norms with a building density of less than 36%.

(2)

Building height

Through the simulation combined with the outdoor wind environment evaluation standards of Hanjiang River’s Chuan Dao area, Shannan, from Figure 10b, it can be concluded that the building height on both sides of the street and the wind speed in the street are positively correlated; the higher the heights of the buildings on both sides of the street, the faster the wind speed in the street. When the building height is 6 m, 11 m, or 15 m, the wind environment of the street can meet the wind environment evaluation standard. However, the higher the building height, the more complicated the wind environment in the alley, so the building height should not be too large. When the building height is 15 m, the maximum wind speed is close to the limit value of 5 m/s, so it is appropriate to keep the building height below 15 m.

(3)

Street width

Through the simulation combined with the Hanjiang River area’s outdoor wind environment evaluation standards, from Figure 10c, it can be concluded that the street width and the wind speed are positively correlated; the larger the street width, the faster the wind speed in the street, meaning an increase in the street width is conducive to airflow. When the street width is too narrow, it makes the human body feel too depressed and is not conducive to airflow, but when the street width is too large, due to the increase in angular airflow, there will be a wind vortex, resulting in the local wind environment being unstable, which is not conducive to a good street wind environment. Combined with the actual land situation, to meet the local demand, the main street width of 11 m in the case of vehicular traffic is appropriate, the width of 6 m for secondary streets is appropriate, and for streets that vehicles do not pass, the width of 3~6 m is appropriate.

4. Conclusions

At present, wind environment research is mostly focused on urban settlements, and there are fewer studies on the wind environment in rural areas. For the villages and towns in the Hanjiang River’s Chuan Dao area in Southern Shaanxi, we used a literature research, field research, summarization, and numerical simulation research to conduct a quantitative analysis and qualitative analysis to propose wind environment evaluation standards suitable for the area. By analyzing the types of street layouts and street forms, the wind environment characteristics of villages and towns in the Hanjiang River’s Chuan Dao region of Southern Shaanxi are summarized. We compare the wind environment characteristics of various types of layouts and forms with the evaluation standards, summarize the indicators that may affect the wind environment of the street spaces, and explore the relationship between the indicators of the street space and the wind environment in the Hanjiang River’s Chuan Dao area.

4.1. Results

(1)

Through on-site research, questionnaires, and wind environment measurements, it was found that the widths of streets and alleys in the Hanjiang River’s Chuan Dao area range from 3.5 m to 15.6 m, and the number of building floors is mostly below five, with the height of building floors being around 3.6 m. The main street of the Zhuge Ancient Township is oriented parallel to the dominant wind direction, while the main streets of the rest of the villages and towns are perpendicular to the dominant wind direction. Through the questionnaire survey, it was summarized that most of the respondents are dissatisfied with the wind environment of the village and town streets in the winter and summer, which is mainly reflected in the poor ventilation leading to hot and stuffy air in the summer, and due to pollutants not being able to be effectively discharged from the streets in the winter, causing the odors to remain for a long time. Through the wind environment measurement of Lefeng Village in the Shangyuan Guan Township, it was found that the overall wind speed inside the streets and alleys is slow, and there are very few cases of wind speeds greater than 1 m/s, which makes it difficult to reach the standard of a comfortable wind environment.

(2)

We summarized the relevant wind environment theories in the literature and determined that there is a relationship between the wind environment and the layout of streets and alleys in villages and towns as well as the layout of buildings from the perspectives of numerical simulation and human habitat environment science. Numerical simulation was chosen to study the wind environment in the street space of the Hanjiang River’s Chuan Dao area in Southern Shaanxi Province. Combined with the climatic characteristics of the Hanjiang River’s Chuan Dao area, we summarized the existing wind environment comfort evaluation standards at pedestrian heights at home and abroad and put forward the outdoor wind environment evaluation requirements applicable to the Hanjiang River’s Chuan Dao area during the winter and summer seasons in six aspects, namely the wind speed, wind vortex, wind speed ratio, wind speed amplification coefficient, air pollutant concentration, and wind pressure difference.

(3)

There are three types of internal streets and alleys, namely “I”-, “T”-, and “X”-shaped streets. By analyzing the simulation results, it could be seen that except for the winter wind speed, all other wind environment indicators do not meet the requirements of a comfortable street wind environment. Among the villages and towns with a grid layout, those with open streets and alleys, a low density of buildings in streets and alleys, and no obvious obstructions at the entrance of the windward side of the dominant wind direction in the summer have better wind environment comfort in the winter and summer seasons. Buildings causing a high degree of enclosure in streets and alleys, narrow street spaces, and street and alley entrances being blocked cause poor wind environment comfort, as a low degree of enclosure in streets and buildings in a staggered arrangement are conducive to a good wind environment. Village and town streets with a herringbone layout should ensure that the entrances facing wind in the dominant direction in the summer should not be greater than the angle of 30°, and there should be no obstructions from buildings. Street entrances should not be facing the dominant wind direction in the winter, but if this cannot be avoided, buildings, plants, etc., should be set up to block the cold wind.

(4)

The impact of building density, building height, and street width on the wind environment is more obvious in the streets of the Hanjiang River’s Chuan Dao villages and towns in Southern Shaanxi Province. According to the characteristics of the village and town buildings in the Hanjiang River’s Chuan Dao area and the characteristics of the simulation study, the building density and wind speed have a negative correlation, where the greater the building density, the slower the wind speed, showing that the region’s building density should be about 36%. The building height and wind speed in the street have a positive correlation, where the higher the buildings on both sides of the street, the faster the wind speed inside the street, so the building height on both sides of the street should be below 15 m. The street width and wind speed are positively correlated; the wider the street, the greater the wind speed. A street where people and vehicles pass should have a width of 6 to 11 m, and in other cases, it should be 3 to 6 m.

(5)

Villages and towns with internal streets and alleys in the “T” and “X” shapes in the Hanjiang River’s Chuan Dao area, South Shaanxi are encouraged to change the design of corner buildings and combine the layouts of parks and squares to increase the amount of air inflow into the streets and alleys to improve the street wind environment. At the level of street space, through the study of street scale, the reasonable height-to-width ratio of streets in this area ranges between 0.5 and 1.5. In areas with high building density, methods of creating open spaces and building setbacks should be adopted to minimize building density and achieve good ventilation. Since the prevailing winds in this area are in opposite directions in the winter and summer, a progressive building height layout is proposed, with building heights arranged from low to high on the windward side of the prevailing winds in the summer to improve the ventilation effect of streets and alleys while blocking the cold winds in the winter.

4.2. Improvement Strategies and Prospects

Through the above research content as the basis, combined with some of the existing research results, some scholars, through alternative auxiliary design optimization to improve the urban wind environment, also provide a solution to improve the urban wind environment under different design problem scales, design sample sizes, and levels of urban airflow [54,55]. The use of an “elevated” building design is proposed to improve the urban wind environment [43,56,57,58], and scholars have argued that architects should prioritize building layouts, building heights in boundary zones, and building shapes, as these factors significantly affect the outdoor wind conditions in cities. Other scholars have proposed a clustered urban development model to create a network of wind corridors to analyze outdoor ventilation and optimize it based on spatial patterns [59,60].

Through the existing studies and the results of this paper, this paper proposes corresponding suitability optimization strategies mainly for the summer by taking into account wind protection in the winter from both the layout and space perspectives to improve the wind environment of village and town streets and alleys in the Hanjiang River’s Chuan Dao area in Southern Shaanxi. In the overall layout of village streets and alleys, the streets and alleys constitute the main ventilation corridors of the village and towns and play an important role in the overall wind environment inside the village and towns; they need to correctly guide the dominant wind direction in the winter, as a wind speed that is too fast leads to a drop in temperature, which affects thermal comfort, and at the same time, it can make the pollutants inside the streets and alleys proliferate over time. In the summer, wind flow can be made more effective in the village and towns to encourage the stuffy air to discharge quickly and reduce the hot air in the summer. In the summer, under the dominant wind direction, the wind effectively flows to all parts of the village and town, prompting the air to be discharged quickly, reducing the temperature, and avoiding the heat island effect. The more regular layout is due to the high degree of building enclosure, which blocks the wind, resulting in a poorer wind environment in both the winter and summer seasons. Therefore, streets and lanes should be open, with large streets being combined with small streets, which is conducive to the penetration of airflow. Street orientation also affects the internal wind environment of the street. In the winter, under the dominant westerly wind direction, in the village and town, the entrances and exits of the street facing the west side should not be greater than 30° to prevent the wind from blowing directly into the interior of the street; this can effectively prevent the cold wind from entering the interior of the building in the winter and improve the degree of comfort of the human body [61].

”T”- and “X”-shaped streets inevitably cause a poor wind environment poor form is inevitable, so public spaces should be optimized to allow people to participate in outdoor activities and rest, and at the same time, the wind environment has a crucial significance. The public open space also plays an important role in urban ventilation, which is of great significance to the local emblematic climate.

Through the simulation results of the building height and street width, the relevant street aspect ratios are 0.5, 0.6, 1, 1.1, 1.5, and 2. By comparing the average wind speed of different aspect ratios, the larger the street aspect ratio is, the faster the wind speed is, and there is no change in the wind speed when the street aspect ratio is more than 1.5; with an aspect ratio of 0.5, the wind speed is close to the standard value, and when the street aspect ratio is too small, the wind speed will be low. According to the simulation results, the street width in the Hanjiang River’s Chuan Dao area should not be too large. Therefore, it is more reasonable to keep the street width ratio between 0.5 and 1.5 in Chuan Dao’s villages and towns.

Finally, by comparing these results with previous studies, this paper shifts the focus of the study from cities to villages and towns, focusing on the comfort of the street wind environment in villages and towns, and the study area is also more representative. However, there are still some shortcomings in this study; for example, there are many other factors affecting the wind environment in the street space, such as similar villages and towns at different altitudes, the vegetation coverage of village and town streets, and larger decorative structures. Other scholars’ views on the influence of architectural morphology on the wind environment can also be researched in the future. The shortcomings of this study and possible future research directions are summarized as follows:

(1)

The wind environment is a comprehensive and holistic system, and the wind environment is also affected by many factors, so this study only focuses on the street layout and street space through the simulation of the ideal model, which causes some limitations.

(2)

It is also necessary to study the influence of the internal space of street building compounds on the wind environment. Factors affecting the microclimate, such as plant and water bodies, need to continue to be studied.

(3)

The study of the wind environment of villages and towns at different altitudes has limitations for the time being, and the applicability of this study to areas with lower altitudes needs to be studied, so future research can be carried out in this perspective.