Numerical Analysis of Unsteady Internal Flow Characteristics in a Bidirectional Axial Flow Pump
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript is entitled " Numerical Analysis of Unsteady Internal Flow Characteristics in a Bidirectional Axial Flow Pump". The authors had analyzed the internal flow and unsteady characteristics of an S-shaped hydrofoil bidirectional axial pump by numerical simulation and verified the reliability of the numerical simulation by model test. This study was carried out to investigate the phenomenon of low efficiency and hydraulic instability in the reverse operation of the bidirectional axial pump, specifically to analyze the internal flow, time-frequency characteristics of pressure pulsation on the surface of the impeller and the pump device, and transient force on the impeller under different operating conditions of the bidirectional axial pump in forward and reverse operation. However, the manuscript's processing of some of the data doesn't directly reflect the article's research purpose. Therefore, MINOR revision has to be done before this manuscript could be accepted for publication in the Sustainability.
1 At the end of the introduction, the authors' explanation of the research methodology, research ideas, and research objectives of this study is not clear enough to facilitate the readers to understand this article quickly.
2 In the second section, the authors have not elaborated enough on the methods and Governing Equations, which should be added to the section.
3 In section 3.3, the introduction of pressure pulsation coefficients and the acquisition of the radial and axial force, the authors should add this section to increase the rigor of the study.
4 In section 3.4, the authors provide a detailed analysis of the time-frequency characteristic data of the pumping de, but the section on the relevant connections to the purpose of the study is lacking.
5 The formatting of some figures in the paper lacks standardization, such as the inconsistent specifications of the comparison graphs in Figures 4 and 9. I suggest that the authors improve the format and details of the paper to reflect the rigor of the authors in their scientific work.
6 Authors should improve the standardization of their writing. For example, variables need to be italicized, any symbols that appear should be explained, and all formulas should be numbered. I suggest adding the nomenclature in the article.
Comments on the Quality of English Language
Minor editing of English language required
Author Response
Response to Reviewer 1 Comments
We sincerely thank the editor and all reviewers for their valuable feedback that we have used to improve the quality of our manuscript. Our responses are given in red font and changes/additions to the manuscript are given in red text.
Question1: At the end of the introduction, the authors' explanation of the research methodology, research ideas, and research objectives of this study is not clear enough to facilitate the readers to understand this article quickly.
Reply: Thanks for the suggestion. We have re-written the last paragraph of the introduction according to the Reviewer’s suggestion the last paragraph of the introduction, as follows:
Bidirectional axial flow pumps produce more serious vibration and noise in operation. At present, there are fewer studies on bidirectional axial pumps, its internal flow mechanism has not been fully grasped, and the design and optimization methods of bidirectional axial pumps are immature. For better understanding of the flow mechanism and pressure pulsation characteristics of bidirectional axial flow pumps under unsteady operating conditions, which is used to improve the operational stability of bidirectional axial flow pumps. Numerical simulation method is used to analyze the internal flow field of bidirectional axial pump by unsteady numerical calculation and analyze its unsteady flow characteristics. This paper provides a reference for the hydraulic design and optimization of bidirectional axial pump. It has been marked in red font.
Question2: In the second section, the authors have not elaborated enough on the methods and Governing Equations, which should be added to the section.
Reply: Thanks for the suggestion. According to the expert 's suggestion, this part has been added to Section 2 ，and section 2.3 is Governing equations and Turbulence model. It has been marked in red font.
Question3: In section 3.3, the introduction of pressure pulsation coefficients and the acquisition of the radial and axial force, the authors should add this section to increase the rigor of the study.
Reply: Thanks for the suggestion. According to the expert 's suggestion, we have introduced relevant references and formulas to elaborate on this section. It has been marked in red font.
Question4: In section 3.4, the authors provide a detailed analysis of the time-frequency characteristic data of the pumping de, but the section on the relevant connections to the purpose of the study is lacking.
Reply: Thanks for the suggestion. According to the expert 's suggestion, we have added the related content in section 3.4. It has been marked in red font.
Question5: The formatting of some figures in the paper lacks standardization, such as the inconsistent specifications of the comparison graphs in Figures 4 and 9. I suggest that the authors improve the format and details of the paper to reflect the rigor of the authors in their scientific work.
Question6: Authors should improve the standardization of their writing. For example, variables need to be italicized, any symbols that appear should be explained, and all formulas should be numbered. I suggest adding the nomenclature in the article.
Reply: Thanks for the suggestion，an excellent paper does need better specification. I have perfected the writing norms.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThis study analyzes the unsteady flow characteristics of a bidirectional axial pump.
1- The paper's novelty appears to be limited, where the plagiarism detection exceeds 40%, which is considered unacceptable.
2- Please rewrite the paper abstract to be more directive and to contain your contributions and the work method.
3- No related work section.
4- Try to clearly identify and highlight the research problem.
5- Section 2 is about simulation model and numerical results, where the description of your contribution and your method?
6- The obtained results show the comparison between testing and simulation only, the results should be compared with recent references also.
7- English proofreading is necessary.
8- Too long conclusion, the paper conclusion is not written in a good way. Please enhance the conclusion by incorporating a quantitative summary of the results for a more comprehensive understanding.
Comments on the Quality of English LanguageEnglish proofreading is necessary.
Author Response
Response to Reviewer 2 Comments
We sincerely thank the editor and all reviewers for their valuable feedback that we have used to improve the quality of our manuscript. Our responses are given in red font and changes/additions to the manuscript are given in red text.
Question1: The paper's novelty appears to be limited, where the plagiarism detection exceeds 40%, which is considered unacceptable.
Reply: Thanks for the suggestion. We have reduced the similarity parts when revising the manuscript.
Question2: Please rewrite the paper abstract to be more directive and to contain your contributions and the work method.
Reply: Thanks for the suggestion. According to the expert 's suggestion, the abstract has been have re-written，contributions and the work method have been added.
Abstract: A bidirectional axial flow pump that utilizes an S-shaped hydrofoil design exhibits low efficiency and hydraulic instability when operated in reverse. In order to understand the unsteady flow characteristics of bidirectional axial pump under different operation conditions, the SST k-ω turbulence model is applied to carry out a three-dimensional unsteady numerical simulation of the full flow channel of bidirectional axial pump. The reliability of the numerical calculation model was verified by comparing it with the experimental head and efficiency. The pressure pulsation characteristics on the impeller surface and the pump device under different operation conditions and the transient forces on the impeller were analyzed. The results show that the head and efficiency in reverse operation are lower than forward operation and the flow streamline of the impeller outlet area is more turbulent in the reverse operation condition. The monitoring points at the inlet and the top of the impeller surface show the largest pressure pulsation amplitude. The radial and axial forces on the impeller in reverse operation are greater than those in forward operation. Under reverse 1.0Qdes condition, the average pressure pulsation amplitude at the inlet of the impeller is 19.2 times and 5.7 times of that at the inlet of the guide vane and the outlet of the impeller. The study provides a reference for the hydraulic design and optimization of bidirectional axial flow pumps
Question3: No related work section.
Reply: Thanks for the suggestion. According to the expert 's suggestion, the related work section has been added to abstract.
Question4: Try to clearly identify and highlight the research problem.
Reply: Thanks for the suggestion. According to the expert 's suggestion, the related research problem has been added to the last paragraph of the introduction. It has been marked in red font.
Bidirectional axial flow pumps produce more serious vibration and noise in operation. At present, there are fewer studies on bidirectional axial pumps, its internal flow mechanism has not been fully grasped, and the design and optimization methods of bidirectional axial pumps are immature. For better understanding of the flow mechanism and pressure pulsation characteristics of bidirectional axial flow pumps under unsteady operating conditions, which is used to improve the operational stability of bidirectional axial flow pumps. Numerical simulation method is used to analyze the internal flow field of bidirectional axial pump by unsteady numerical calculation and analyze its unsteady flow characteristics. This paper provides a reference for the hydraulic design and optimization of bidirectional axial pump.
Question5: Section 2 is about simulation model and numerical results, where the description of your contribution and your method?
Reply: Thanks for the suggestion. According to the expert 's suggestion, the contribution and method have been added to Section 2 ，and section 2.3 is Governing equations and Turbulence model. It has been marked in red font.
Question6: The obtained results show the comparison between testing and simulation only, the results should be compared with recent references also.
Reply: Thanks for the suggestion. Relevant literature has been introduced. The model test validates the model for the numerical simulation to demonstrate the reliability of the numerical simulation, and subsequently there is a consideration of pressure pulsation test on the pump model. It has been marked in red font.
Question7: English proofreading is necessary.
Reply: Thanks for the suggestion. Errors in the English of the manuscript have been corrected after several careful English proofreading. The errors have been corrected and marked in red.
Question8: Too long conclusion, the paper conclusion is not written in a good way. Please enhance the conclusion by incorporating a quantitative summary of the results for a more comprehensive understanding.
Reply: Thanks for the suggestion. According to the expert 's suggestion, we have condensed the conclusions section and included a quantitative summary in the conclusions. It has been marked in red font.
4 Conclusion
Bidirectional axial flow pumps operating in reverse are characterized by low efficiency and hydraulic instability. In this paper, the S-airfoil blades bidirectional axial flow pump device is taken as the object of study, and its non-constant flow characteristics are analyzed, impeller surface and pump device pressure pulsation characteristics, and impeller transient force changes are obtained.
- The head and efficiency in reverse operation are lower than in forward operation at the same flow rate. There is no guide vane to convert the kinetic energy of the fluid into pressure energy under the reverse operation conditions resulting in impeller outlet area flow streamline disorder, this phenomenon with the increase in flow rate and weakened.
- The maximum Cp amplitude on the impeller surface in the circumferential and radial directions is at the inlet and blade top respectively，which corresponds to the location where the blade is usually damaged. The main frequency of Cp on the impeller suction surface changes to the guide vane frequency in reverse operation, which indicates that the suction surface of the impeller in reverse operation is greatly influenced by the front guide vane.
- The FZ and FR on the impeller under low flow conditions are large and operation under low flow conditions should be avoided as much as possible. The FZ and FR of the impeller in reverse operation are greater than in forward operation for the same flow conditions.
- Analysis of the Cp characteristics of a pumping device for optimum conditions. The Cp amplitude in the impeller inlet area is larger, indicating that the dynamic and static interference between the impeller and guide vane is aggravated under reverse operation condition, which can be mitigated by the reasonable hydraulic design of the impeller and guide vane to improve the operation stability of the bidirectional axial flow pump.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for Authors1. It is important to note that several references have been overlooked in the text but are listed in the references section, such as references 3, 9, 10,11, 16, 17, 18 and 19. Therefore, it is necessary to thoroughly review and cross-check all references to ensure their proper inclusion within the text.
2. Can you elaborate on the factors contributing to the increased turbulence in the flow streamline at the impeller outlet area during reverse operation? Are there any design considerations or modifications that could potentially mitigate this issue?
3. In your analysis of the unsteady flow characteristics, what are the potential consequences of the observed pressure pulsation amplitudes at the inlet and top of the impeller? How might these affect the overall performance and durability of the pump?
4. The aim and innovation of this paper should be highlighted in the last paragraph of the introduction.
5. It is important to clarify that specifying the number of meshes as 75.9 million was incorrect. Instead, it would be more accurate to provide details such as the element size, total number of nodes, and elements used in the computational model.
6. Additionally, considering the large number of meshes involved, it would be beneficial to mention the computational time required to solve this problem.
7. Has any mesh quality analysis been carried out on the proposed FE model (aspect ratio, Jacobian rate, etc.)? Please justify.
8. Clarify this statement "The total calculation time is the time of 10 rotation of the impeller, which is 0.331034482"seconds.
9. Is there a correlation for the number of peaks and valleys with the number of guide vanes?
10. What factors contribute to the fluctuation in amplitude along the length of a blade, starting from the hub and extending towards the tip?
11. The numerical and experimental components lack rigor and fail to provide essential information necessary for the replication of the proposed experimental and numerical simulations.
12. In the conclusion, it could be interesting to underline and deepen the importance of the results found and what could be the implications. Conclusions need extensive improvements.
Comments on the Quality of English Language
Moderate editing of English language required.
Author Response
Response to Reviewer 3 Comments
We sincerely thank the editor and all reviewers for their valuable feedback that we have used to improve the quality of our manuscript. Our responses are given in red font and changes/additions to the manuscript are given in red text.
Question1: It is important to note that several references have been overlooked in the text but are listed in the references section, such as references 3, 9, 10,11, 16, 17, 18 and 19. Therefore, it is necessary to thoroughly review and cross-check all references to ensure their proper inclusion within the text.
Reply: Thanks for the suggestion. We have identified these references further and have removed a portion of the vaguely references to achieve literature citation accuracy. It has been marked in red font.
Question2: Can you elaborate on the factors contributing to the increased turbulence in the flow streamline at the impeller outlet area during reverse operation? Are there any design considerations or modifications that could potentially mitigate this issue?
Reply: Thanks for the suggestion. Thanks for the suggestion. After the fluid is accelerated by the impeller rotation, the velocity at the rim is larger, the velocity at the hub is smaller, and there exists a region of lower flow velocity in the intermediate region, which leads to turbulence of the flow streamline in the outlet area of the impeller. With the increase of flow rate, this phenomenon will be weakened. Through reasonable design in the bidirectional axial flow pump front and rear are installed guide vane, guide vane recovery energy, the kinetic energy of the fluid is converted into pressure energy, so as to alleviate this phenomenon. It has been marked in red font.
Question3: In your analysis of the unsteady flow characteristics, what are the potential consequences of the observed pressure pulsation amplitudes at the inlet and top of the impeller? How might these affect the overall performance and durability of the pump?
Reply: Thanks for the suggestion. Pressure pulsations in hydraulic machinery are generated periodically in time, and the generation of pressure pulsations is often accompanied by noise and vibration, mechanical fatigue damage, and lower efficiency. Impeller inlet and top positions pressure pulsation amplitude is larger, may cause pump operation instability low efficiency， noise and vibration, damage at the inlet and the top of the impeller, which is consistent with the axial flow pump impeller usually damage location. It has been marked in red font.
Question4: The aim and innovation of this paper should be highlighted in the last paragraph of the introduction.
Reply: Thanks for the suggestion. A revision has been made to the last paragraph of the introduction, as follows:
Bidirectional axial flow pumps produce more serious vibration and noise in operation. At present, there are fewer studies on bidirectional axial pumps, its internal flow mechanism has not been fully grasped, and the design and optimization methods of bidirectional axial pumps are immature. For better understanding of the flow mechanism and pressure pulsation characteristics of bidirectional axial flow pumps under unsteady operating conditions, which is used to improve the operational stability of bidirectional axial flow pumps. Numerical simulation method is used to analyze the internal flow field of bidirectional axial pump by unsteady numerical calculation and analyze its unsteady flow characteristics. This paper provides a reference for the hydraulic design and optimization of bidirectional axial pump. It has been marked in red font.
Question5: It is important to clarify that specifying the number of meshes as 75.9 million was incorrect. Instead, it would be more accurate to provide details such as the element size, total number of nodes, and elements used in the computational model.
Reply: Thanks for the suggestion. The erroneous content has been corrected and it has been marked in red font.
Question6: Additionally, considering the large number of meshes involved, it would be beneficial to mention the computational time required to solve this problem.
Reply: Thanks for the suggestion. a larger number of meshes results in more accurate numerical calculations, but a larger number of meshes requires greater computational resources. The total number of meshes was determined to be 7.59 million is after mesh independence validation, and this section 2.2 has been added to the manuscript.
Question7: Has any mesh quality analysis been carried out on the proposed FE model (aspect ratio, Jacobian rate, etc.)? Please justify.
Reply: Thanks for the suggestion. This part has been added to section 2.2.
Question8: Clarify this statement "The total calculation time is the time of 10 rotation of the impeller, which is 0.331034482"seconds.
Reply: Thanks for the suggestion. The impeller speed is set to 1450 r/min, and time needs to be taken as a variable in the analysis of unsteady calculation. 3° rotation of the impeller is chosen as a time step, i.e., 0.000344828 seconds, and the total computational time is 10 revolutions of the impeller, which is a total of 3600°, i.e., 0.331034482 seconds, which can ensure the accuracy of the computational results. The section has been added to the manuscript and it has been marked in red font.
Question9: Is there a correlation for the number of peaks and valleys with the number of guide vanes?
Reply: Thanks for the suggestion. The time domain of pressure pulsations at the monitoring point on the impeller surface produces 7 peaks and valleys, which are related to the number of guide vanes. The main frequency of pulsation at the monitoring point of the pump device is the impeller rotation frequency, the impeller is the rotating part of the axial pump, the rotating pressure of the impeller will alternately change to produce, the frequency of the guide vane has less influence, so the number of peaks and valleys and the number of blades of the impeller has a direct correlation with the number of guide vane has no correlation. The response has been revised in the manuscript on page 14and. It has been marked in red font.
Question10: What factors contribute to the fluctuation in amplitude along the length of a blade, starting from the hub and extending towards the tip?
Reply: Thanks for the suggestion. In the same cross-section, the Cp amplitude decreases as the monitoring point moves from the top of the blade to the hub, which is related to the blade design that is the distribution of loads along the blade spread. The response has been revised in the manuscript on page 14. It has been marked in red font.
Question11: The numerical and experimental components lack rigor and fail to provide essential information necessary for the replication of the proposed experimental and numerical simulations.
Reply: Thanks for the suggestion. The model test validates the model for the numerical simulation to demonstrate the reliability of the numerical simulation, and subsequently there is a consideration of pressure pulsation test on the pump model.
Question12: In the conclusion, it could be interesting to underline and deepen the importance of the results found and what could be the implications. Conclusions need extensive improvements.
Reply: Thanks for the suggestion. According to the expert 's suggestion, the conclusion has been modified the importance of the results found and what could be the implications have been added.
4 Conclusion
Bidirectional axial flow pumps operating in reverse are characterized by low efficiency and hydraulic instability. In this paper, the S-airfoil blades bidirectional axial flow pump device is taken as the object of study, and its non-constant flow characteristics are analyzed, impeller surface and pump device pressure pulsation characteristics, and impeller transient force changes are obtained.
- The head and efficiency in reverse operation are lower than in forward operation at the same flow rate. There is no guide vane to convert the kinetic energy of the fluid into pressure energy under the reverse operation conditions resulting in impeller outlet area flow streamline disorder, this phenomenon with the increase in flow rate and weakened.
- The maximum Cp amplitude on the impeller surface in the circumferential and radial directions is at the inlet and blade top respectively，which corresponds to the location where the blade is usually damaged. The main frequency of Cp on the impeller suction surface changes to the guide vane frequency in reverse operation, which indicates that the suction surface of the impeller in reverse operation is greatly influenced by the front guide vane.
- The FZ and FR on the impeller under low flow conditions are large and operation under low flow conditions should be avoided as much as possible. The FZ and FR of the impeller in reverse operation are greater than in forward operation for the same flow conditions.
- Analysis of the Cp characteristics of a pumping device for optimum conditions. The Cp amplitude in the impeller inlet area is larger, indicating that the dynamic and static interference between the impeller and guide vane is aggravated under reverse operation condition, which can be mitigated by the reasonable hydraulic design of the impeller and guide vane to improve the operation stability of the bidirectional axial flow pump.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsAccept in present form
Reviewer 3 Report
Comments and Suggestions for AuthorsThis revision has significantly improved the manuscript. The authors have satisfactorily addressed most of my concerns.
Comments on the Quality of English LanguageModerate editing of English language required.
