Design and Optimization of Fluid Machinery, 2nd Edition

Abstract

Fluid machinery is widely used in industrial production, particularly in industries such as chemical engineering, agriculture, and water resources. With the development of industrial society, the application scope of fluid machinery continues to expand, leading to higher demands for its performance. There is an urgent need to develop and manufacture fluid machinery with superior performance, which requires the optimization design of fluid machinery. This must focus on aspects such as flow mechanisms and energy losses, exploring the factors that affect fluid machinery’s performance in order to improve it through the design or modification of the fluid machinery structure. This Special Issue’s primary focus is just that. After a thorough peer review process, 13 articles were accepted for publication. These articles cover the categories of research detailed in the following sections.

1. Influence of Flow Conditions on Hydrodynamic Characteristics of Fluid Machinery

Under different flow conditions, fluid machinery often shows different flow characteristics. In the case of simple fluid machinery, Ma et al. [Contribution 1] studied the effect of the Reynolds number on the flow-induced vibrations of a cylinder. They found that, for a smooth cylinder, the peak amplitude ratio increases as the Reynolds number rises. Higher Reynolds numbers increase the complexity and nonlinearity of the flow field, which in turn affects the predictability and control of the vibration behavior. In the transient characteristics of rotating fluid machinery, Tan et al. [Contribution 2] investigated the transient behavior of a single-blade centrifugal pump under variable frequency speed control. They compared the variations in radial force, flow field distribution, and shaft power across different scenarios. The study found that a gradually decreasing acceleration scheme can improve operational stability, reduce fluctuations in radial force, and ensure a more uniform pressure distribution. Li et al. [Contribution 3] studied the impact of valve opening on the dynamic characteristics of the rotor structure during the transient startup of a multistage pump. They found that, under different valve openings, the maximum deformation of the pump shaft occurred at the contact surface between the intermediate impeller and the pump shaft. As the valve opening increased, the maximum deformation of the pump shaft slightly decreased. Modal analysis is the primary method for studying mechanical stress variations. Zhang et al. [Contribution 4] investigated the issue of impeller misalignment in axial flow impellers through modal variation techniques. Their study exhibited that the eccentricity of the impeller had a minimal impact on hydraulic performance, but that impeller misalignment caused a sharp increase in radial force. Additionally, the eccentricity significantly influenced pressure fluctuations, with the impact primarily reflected in the relationship between impeller frequency and pressure pulsations.

2. Internal Flow Mechanism and Energy Loss Analysis of Fluid Machinery

The flow mechanism is often the primary criterion for evaluating the performance of fluid flow characteristics in fluid machinery. Cheng et al. [Contribution 5] investigated the effect of temperature on the hydraulic performance of a magnetically driven vortex pump. They discovered that as the medium temperature increased, both the pump head and efficiency improved. The variations in hydraulic performance at different fluid temperatures were primarily due to changes in the internal flow field vorticity. Chen et al. [Contribution 6] investigated the transient flow characteristics during the startup process of a multistage centrifugal pump system before its operation. They observed that a shorter startup time enhances the transient effects, with the pump head initially increasing rapidly and then stabilizing. The vortex structure displayed periodic development and dissipation. Energy loss is a key concern in fluid machinery. Meng et al. [Contribution 7] conducted unsteady calculations of the internal flow field in a seven-stage centrifugal pump to reveal the internal loss characteristics of multistage pumps. The results showed that turbulence dissipation entropy is the primary source of energy loss, and that the impeller, diffuser, and discharge chamber are the main areas where energy losses occur in the multistage pump. The entropy production value of the first-stage impeller was significantly higher than that of the other impellers, while the entropy production value of the first-stage diffuser was notably lower than that of the other diffusers. In addition, Liu et al. [Contribution 8] carried out multi-parameter optimization of a wide-range centrifugal pump using a genetic algorithm. Through sensitivity analysis, they identified that the blade wrap angle was the most significant factor affecting pump efficiency, with an impact rate of 83.6%. They also compared the energy loss within the pump before and after optimization, and found that, with the increase in efficiency, the energy loss within the pump decreased accordingly after optimization.

3. Geometry of Fluid Machinery and Multiphase Flow

Currently, research on the structure of fluid machinery is divided into fluid machinery design and fluid structure improvement. In fluid machine design, Deng et al. [Contribution 9] designed a novel modular suspended underwater dredging robot for the biochemical reaction tanks in groundwater treatment plants. This robot can maintain stable operation even in the turbulent flow generated by the pump, achieving a combination of suction and pump jet flow. In terms of fluid mechanical structure improvement, Xu et al. [Contribution 10] investigated the effect of the blade wrap angle on the internal flow and pressure fluctuation characteristics of a turbine. The results showed that the maximum efficiency was achieved with a blade wrap angle of 35°, and that as the blade wrap angle increased, the flow rate at the highest efficiency gradually decreased. In addition, Wang et al. [Contribution 11] studied the impact of cam top clearance on the performance of high-speed centrifugal pumps and found that reducing the cam top clearance plays a significant role in improving pump performance and reducing energy loss. Under certain operating conditions, multiphase flow within the pump is often the focal point of attention. Han et al. [Contribution 12] studied the mixing of binary particles in a gas–solid fluidized bed under different resistance models. They found that the Ergun, Gidaspow–Bezburuah–Ding, and Hill–Koch–Ladd models exhibited excellent particle mixing uniformity. Regarding pressure drop, the Huilin–Gidaspow, Gidaspow, Bezburuah, and Ding models demonstrated smaller and more stable pressure drop fluctuations. Shen et al. [Contribution 13] used an orthogonal experimental design method to simulate the turbulence model, evaporation coefficient, and condensation coefficient, analyzing the impact of these parameters on the NPSH peak of high-specific-speed centrifugal pumps. By comparing the numerical results with experimental data, they developed a numerical model that closely matched the experimental cavitation characteristics.

In summary, this Special Issue covers research on the hydraulic characteristics, flow mechanisms, energy losses, geometric structures, and multiphase flow in fluid machinery, providing valuable insights for enhancing the performance of fluid machinery. It is important to note that modifying the structure of fluid machinery is a powerful approach to optimizing its performance, and should be further expanded upon in the future. The papers in this Special Issue offer valuable references for the development of the fluid machinery industry, contributing to the advancement of industrial society. Additionally, we are delighted to announce that contributions for the third volume of the Special Issue are now being solicited, and we encourage experts and scholars in the field to participate actively. For more information, please visit the following link: https://www.mdpi.com/journal/water/special_issues/2BGP3XJNER (accessed on 21 February 2025).