Review Reports

Round 1

Reviewer 1 Report

This is a well designed study that deserves to be published in Applied Sciences. There are two major issues that I would like the authors to address, the first in the english language and the second is the reference list. Both need a major improvement. For the first, I reccomend that they seek the help of a native english speaker, as sometimes it is hard to understand the meaning, and for the second I think that they should expand the list to 30 references (17 is simply to little for a manuscript). 

Author Response

Point 1: For the first, I reccomend that they seek the help of a native english speaker, as sometimes it is hard to understand the meaning.

Response 1: I will revise the manuscript and use the paper service provided by MDPI for English polishing

 

Point 2: For the second I think that they should expand the list to 30 references (17 is simply to little for a manuscript).

Response 2: I will add references to over 30 articles .

Author Response File: Author Response.docx

Reviewer 2 Report

The paper presents the results of a joint numerical (CFD) and experimental research on the performance improvement of an air inflow pipe for automotive application. A CFD analysis was first carried out to investigate the effect of shape changes in the pipe inlet and its bending section on the total pressure loss. After selecting the minimum pressure loss configuration, the authors built simplified experimental mock-ups of both the baseline and proposed inflow pipes to validate their approach. They found systematic reduction in the total pressure loss for the “optimized” device also in this case, which confirms the numerical results.

The activity described by the authors certainly constitutes a careful execution of an industrial workflow for the performance optimization of a fluid system. Nonetheless, the present reviewer’s opinion is that the manuscript is unsuitable for publication on Applied Sciences, for two main reasons:

11)      The fact that fitting the geometrical discontinuities of a curved pipe yields reduction of the total pressure loss is perhaps a bit obvious. There are reliable formulas/empirical methods on this topic, which make CFD redundant for this case.

22)      The analysis is focused, as specified by the authors at page 3 of their manuscript, on a single engine geometry, of a specific brand. It is hard to say, at this stage, if any other researcher can take advantage of the present analysis or if the results illustrated by the authors are specific of their configuration.

Another important issue of this paper is its clarity and word selection, which must be improved. A few examples are given in the following:

line 45 and following: “scholars” should be replaced by “researchers”

lines 72-86 should be omitted, they are very broad and unsuitable for a research paper

lines 88: “physicalist” should be replaced with “physicist”

line 90: Reynolds number definition is too broad, should be specialized for the present case. In addition, the turbulent transition threshold Re=3000 is not universal, the authors should describe this aspect in detail

Equation 2: please provide any reference for this formula. The turbulent intensity is never defined

Figure 3: it is appropriate to define, in this picture, the reference system Oxyz used thereafter, and quote the main geometrical dimensions

Table 1: “Inlet” and “Outlet” are never defined

Figure 4 and following ones: please use the same velocity/pressure min/max levels for all contour plots to allow comparison between different cases. In addition, the contour levels are unreadable, the quality of the pictures must be improved.

Line 208 and following: the term “nephogram” has basically no usage by the engineering community, it should be replaced with “contour plot”

The terms “optimization” and “structural optimization” refer to specific numerical algorithms for functional optimization, which are clearly not used in the paper. The present reviewer suggests to replace them with a more generic “performance improvement” or “pressure loss reduction”

Author Response

Point 1: The fact that fitting the geometrical discontinuities of a curved pipe yields reduction of the total pressure loss is perhaps a bit obvious. There are reliable formulas/empirical methods on this topic, which make CFD redundant for this case.

Response 1: Thank you for your criticism and guidance. I believe that combining CFD simulation with experiments would better illustrate the real situation in actual situations.

 

Point 2: The analysis is focused, as specified by the authors at page 3 of their manuscript, on a single engine geometry, of a specific brand. It is hard to say, at this stage, if any other researcher can take advantage of the present analysis or if the results illustrated by the authors are specific of their configuration.

Response 2: Thank you for your criticism and guidance. The purpose of publishing this article is not only to optimize the performance of a certain engine model, but also to provide a case study for other researchers in the same field. The performance optimization plan proposed in the article can also provide a train of thought for peers.

 

For some of the examples listed below, the paper will also undergo some language polishing and modifications.

Author Response File: Author Response.docx

Reviewer 3 Report

The authors simulate and analyze the internal gas flow field in the intake system of gasoline engine vehicles. The intake pipe is optimized to reduce the total pressure loss between the inlet and the outlet sections of the pipeline. The topic is interesting to me, but the manuscript can be considered for publication after the authors have replied to all the following mandatory remarks:

 

Main comments:

1) In the introduction, the literature review provided by the authors is poor. The previous studies on this subject are only listed, without a discussion. The authors should discuss the state-of-the-art literature. 

2) The authors should present the innovative contribution of the research compared with the state-of-the-art, if any.

3) lines 92-94 -> The authors state that above Re=3000 the flow is turbulent. This is not the “classical” value for pipes (Re=2100-2300 for transitional state and Re=4000 for fully turbulent). The authors should discuss this point. 

4) The authors introduce and describe the model in the results section. The model set-up and the numerical methodology are not results, they should move this part into the 'Materials and Method' section or create a new dedicated section “Simulation set-up”. 

5) The authors state that they simplified the geometry. Which is the impact of this hypothesis on the reliability of the results? 

6) The authors should provide some additional details on the code used. Is it a finite-volume or a finite-element method? Which are the space and time discretization orders?

7) How does the number of cells affect the results? The authors should provide the grid-independency analysis.

8) The authors carry out an optimization procedure by increasing the curvature radius of the air inlet structure and the bending radius. The authors should specify if the optimization of the bending angle is obtained on the geometry after performing the optimization of the air-inlet structure radius or, on the contrary, on the original geometry. If the second optimization is carried out starting from the best condition of the first optimization, what ensures that the result coming out of the second process is the best? Or rather, could there be other combinations of these two parameters that lead to a better result than the one described by the authors (multi-parameters optimization)? 

9) The authors should explain the choice of the range of variation of the optimization parameters. I suggest the author discuss, or at least mention, further details on the optimization procedures on internal flows in pipes (as in Mariotti et al. 2013, 2015, Matsuchima et al. 2006, Nunes et al. 2020) to improve the discussion on optimization procedures and results.

10) Since the authors consider two parameters in their optimization study. I suggest the authors a posteriori evaluate the partial sensitivities (Sobol, 2001) to single out the importance of each of the two parameters on the device performance.

11) The authors should describe the benefits of their parameter choice by comparing it to other possible approaches, e.g., the use of Bezier/splines curves as proposed for internal flows in Mariotti et al. (2013, 2015). These procedures/strategies and the suggested references should also be mentioned among the possible optimization strategies in the paper.

12) The authors should specify the type of resin used in the making of the experimental model.

 

Minor comments:

13) English should be improved.

14) Figure 2 -> The author should add the dimensions in the figure

15) Figures 4, 5, and 6 -> It is not clear where the section is located. I suggest adding the figure of the model and explaining the location of the measurement sections.

 

Suggested references:

-Nunes, M.M. et al. (2020): Systematic review of diffuser-augmented horizontal-axis turbines Renew. Sust. Energ. Rev. 133, 110075. -Mariotti, A. et al. (2013), "Separation control and efficiency improvement in a 2D diffuser by means of contoured cavities" Eur. J. Mech. B/Fluids 41, 138–149
-Sobol, M. (2001). Global sensitivity indices for nonlinear mathematical models and their Monte Carlo estimates Math. Computable Simul. 55(1-3), 271-280

Author Response

Point 1: In the introduction, the literature review provided by the authors is poor. The previous studies on this subject are only listed, without a discussion. The authors should discuss the state-of-the-art literature.

Response 1: The literature review section of the paper has been revised, and the number of references has also been increased.

 

Point 2: The authors should present the innovative contribution of the research compared with the state-of-the-art, if any.

Response 2: The innovative contribution of this study compared to state-of-the-art research has been explained in the text.（This study mainly focuses on reducing the flow resistance of the engine intake system by optimizing the relevant structure of the intake pipe to improve intake efficiency. Moreover, the optimized model will be subjected to flow resistance tests to verify the reliability of the simulation results.）

 

Point 3: lines 92-94 -> The authors state that above Re=3000 the flow is turbulent. This is not the “classical” value for pipes (Re=2100-2300 for transitional state and Re=4000 for fully turbulent). The authors should discuss this point.

Response 3: The range of Reynolds number of pipe flow has been modified.

 

Point 4: The authors introduce and describe the model in the results section. The model set-up and the numerical methodology are not results, they should move this part into the 'Materials and Method' section or create a new dedicated section “Simulation set-up”.

Response 4: A new section has been created for this section called Model establishment and grid division

 

Point 5: The authors state that they simplified the geometry. Which is the impact of this hypothesis on the reliability of the results?

Response 5: The simplified model only made appropriate changes to the external structure of the housing, without much simplification of the air intake port at the front of the intake pipe and the bends in the pipeline. Nevertheless, the simulation results still have ref-erence value.

 

Point 6: The authors should provide some additional details on the code used. Is it a finite-volume or a finite-element method? Which are the space and time discretization orders?

Response 6: It should be noted that the Fluent is based on the finite volume method principle, which divides the continuous region into a series of non-repeating control volumes and calculates and integrates them separately to obtain a similar solution. This study used the common SIMPLE solution algorithm, carry out spatial discretization first and then temporal discretization.

Point 7: How does the number of cells affect the results? The authors should provide the grid-independency analysis.

Response 7: The number of grids obtained in the article is based on grid independence analysis, and the simulation results of the encrypted grid are not significantly different from the current grid.

Point 8: The authors carry out an optimization procedure by increasing the curvature radius of the air inlet structure and the bending radius. The authors should specify if the optimization of the bending angle is obtained on the geometry after performing the optimization of the air-inlet structure radius or, on the contrary, on the original geometry. If the second optimization is carried out starting from the best condition of the first optimization, what ensures that the result coming out of the second process is the best? Or rather, could there be other combinations of these two parameters that lead to a better result than the one described by the authors (multi-parameters optimization)?

Response 8: The optimization of the second bending radius in the article is based on the optimization plan of the inlet structure. If the second optimization is only carried out on the basis of the original model, the effect is obviously not as good as the superposition of the two optimizations.

Point 9: The authors should explain the choice of the range of variation of the optimization parameters. I suggest the author discuss, or at least mention, further details on the optimization procedures on internal flows in pipes (as in Mariotti et al. 2013, 2015, Matsuchima et al. 2006, Nunes et al. 2020) to improve the discussion on optimization procedures and results.

Response 9: Due to the inner diameter of the intake pipe being 60mm and the wall thickness being 2.5mm, in order to avoid the influence of the horn shaped structure on air flow into the intake pipe and the inability to match other components due to the large lateral width of the intake pipe, it is planned to increase the horn shaped radius from 3mm to 15mm, with an interval of 2mm to analyze the changes in radius on inlet flow uniformity and inlet/outlet pressure difference, in order to obtain the optimal radius.

Point 10: Since the authors consider two parameters in their optimization study. I suggest the authors a posteriori evaluate the partial sensitivities (Sobol, 2001) to single out the importance of each of the two parameters on the device performance.

Response 10: Thank you for your suggestion. I will consider adding some content to explain in the paper.

Point 11: The authors should describe the benefits of their parameter choice by comparing it to other possible approaches, e.g., the use of Bezier/splines curves as proposed for internal flows in Mariotti et al. (2013, 2015). These procedures/strategies and the suggested references should also be mentioned among the possible optimization strategies in the paper.

Response 11: The article focuses on optimizing the performance of the intake manifold for a certain model. Currently, it may not be possible to find other optimization solutions related to this, but it can be compared with other similar intake manifolds in terms of research methods.

Point 12: The authors should specify the type of resin used in the making of the experimental model.

Response 12: The sample used in this test is realized by 3D printing technology, and the mate-rial used is a high toughness resin, which has a high deformation temperature. In some high temperature areas, it can avoid deformation of the sample due to excessive tem-perature, which can cause significant differences between the actual object and the data model, affecting the accuracy of the test results.

Minor comments:

Point 13:English should be improved.

Response 13: I will revise the manuscript and use the paper service provided by MDPI for English polishing

Point 14: Figure 2 -> The author should add the dimensions in the figure 2

Response 14: I will add the dimensions to Figure 2

Point 15: Figures 4, 5, and 6 -> It is not clear where the section is located. I suggest adding the figure of the model and explaining the location of the measurement sections.

Response 15: I will explain the selected cross-section accordingly

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

The authors do not satisfactorily answer point 8. The two optimizations should be carried out together and not one following the other. This is a significant limitation of their procedure that should be discussed in the paper. 

The authors do not satisfactorily answer point points 9-11. They do not discuss and cite the 5 suggested references. They do not improve the discussion in the paper on the optimization of ducts for internal flows. 

If they do not address points 8-11, I cannot recommend the publication of the paper.

Author Response

Point 1: The authors do not satisfactorily answer point 8. The two optimizations should be carried out together and not one following the other. This is a significant limitation of their procedure that should be discussed in the paper.

Response 1: Thank you for your criticism and guidance. I have added a discussion on two performance improvement schemes before the conclusion of the paper, and pointed out the order of optimizing strategies for the two structures, and provided corresponding explanations.

 

Point 2: The authors do not satisfactorily answer point points 9-11. They do not discuss and cite the 5 suggested references. They do not improve the discussion in the paper on the optimization of ducts for internal flows.

Response 2: Thank you for your criticism and guidance. I have added relevant discussions on two structural optimization strategies before the conclusion of the paper, and added corresponding references and conducted some discussion and analysis in each optimization plan.

Author Response File: Author Response.docx

Round 3

Reviewer 3 Report

Accept in present form