Analysis of Performance and Noise on an Asymmetric Double-Suction Fan with Non-Uniformity Inlet Conditions
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis paper focuses on the performance and noise of an asymmetric double-suction centrifugal fan under non-uniform inlet conditions. Through performance tests and large eddy simulations, it analyzes the impacts of different inlet conditions and proposes a non-uniform inlet scheme. The research reveals that the inlet area affects the performance, and there are differences in pressure pulsation and noise characteristics under specific conditions. The optimization scheme can enhance performance and reduce noise, providing a reference for fan design. The current research mainly focuses on the performance and noise analysis of the asymmetric double-suction centrifugal fan under specific working conditions. To enhance the universality of the research conclusions, it is recommended that subsequent research expand the range of working conditions to cover more different types of kitchen usage scenarios (such as different cooking powers, different stove layouts, etc.), explore the influence of the air intake conditions on the fan performance and noise under a wider range of working conditions, and provide more comprehensive theoretical support for practical applications. In the conclusion, it is directly stated that Condition 1 is the most unstable. What are the specific actual usage scenarios corresponding to this state, and what are the specific classification criteria? Does it have any specific research significance? The readability of the conclusion in the paper is poor, and it is recommended to make modifications. The clarity of Figures 17, 24, and 26 is insufficient, making them unsuitable for readers to view. It is recommended to replace them with images of higher resolution. In Figures 19-21, a relatively large amount of space is used to show the transient changes in the flow field vortex system between the blade stages. It is recommended to supplement the theoretical explanations to support the pressure changes under different working conditions. What is "acum" in Figure 24, and it is recommended to supplement how it is specifically calculated.
Comments on the Quality of English LanguageSome content needs to be revised and added. Please refer to the specific suggestions for details.
Author Response
Comment1：The current research mainly focuses on the performance and noise analysis of the asymmetric double-suction centrifugal fan under specific working conditions. To enhance the universality of the research conclusions, it is recommended that subsequent research expand the range of working conditions to cover more different types of kitchen usage scenarios (such as different cooking powers, different stove layouts, etc.), explore the influence of the air intake conditions on the fan performance and noise under a wider range of working conditions, and provide more comprehensive theoretical support for practical applications.
[Response1]：We sincerely appreciate the editor's valuable feedback. The recommendation to expand the range of working conditions is reasonable and practical. The current research analyses the performance and noise of asymmetric double-suction centrifugal fans under specific non-uniform inlet conditions. However, kitchen usage scenarios are diverse. In future research, we will consider incorporating different cooking powers, stove layouts, and other factors to create a broader range of working conditions. This will help us more comprehensively investigate the impact of inlet conditions on fan performance and noise. We aim to provide more robust theoretical support for practical applications, thereby enhancing the universality and practical value of the research findings.
Comment2：In the conclusion, it is directly stated that Condition 1 is the most unstable. What are the specific actual usage scenarios corresponding to this state, and what are the specific classification criteria? Does it have any specific research significance?
[Response2]：Condition 1 corresponds to scenarios where the left inlet is open and the right inlet is blocked in actual usage. The inlet operating conditions analysed in this study are determined based on the practical usage of range hoods. Modern range hoods dynamically adjust their inlet conditions and structures in response to the operating status of the cooktops below to enhance the capture of cooking fumes. However, the viscosity of cooking fumes can accumulate over time, causing blockages in the inlet area. Combined with the asymmetry of the volute and the rotation of the impeller, these factors create varying inlet conditions on the left and right sides. This ultimately impacts the aerodynamic and noise performance of the range hood. Consequently, this research offers valuable insights and a foundation for optimising range hoods' and centrifugal fan performance and noise design. In response to your comments, we have made substantial revisions in the part of Analysis of aerodynamic performance to strengthen this connection. Thank you for your understanding.
Comment3：The readability of the conclusion in the paper is poor, and it is recommended to make modifications.
[Response3]：We appreciate the reviewer's feedback regarding the conclusion's readability. We will revise it as follows for clarity and to highlight key points in the part of conclusions :
This study utilizes numerical simulations to explore how various inlet conditions influence the internal flow field and pressure pulsation of a dual-inlet centrifugal fan. The key findings are as follows:
（1）Time-domain analysis indicates that inlet condition 1 is the most unstable. This instability is characterized by significant fluctuations in the pressure coefficient and the presence of broadband signals in the frequency domain. These broadband features are particularly pronounced at measurement point C1, located on the wide impeller, and measurement point D5, located on the narrow impeller.
（2）Analysis of transient vortex structures reveals that the observed broadband characteristics and the absence of the blade-passing frequency at these measurement points are associated with the periodic evolution of large-scale vortices within the flow passage. Under inlet condition 1, the intensity of the vortices peaks due to the alignment between the inlet direction and the impeller's rotation direction, which has a substantial impact on flow within the passage.
（3）Sound quality analysis shows that under inlet condition 1, the sound sharpness is greater than under the other conditions. This observation suggests a higher presence of high-frequency signals in the pressure pulsation near the blade-passing frequency, further linking the flow structures to the characteristics in the frequency domain.
（4）A non-uniform air volume distribution scheme is proposed. This scheme enhances aerodynamic performance and reduces noise discrepancies between the left and right sides, leading to an overall reduction in average loudness by 4 sones.
Comment4：The clarity of Figures 17, 24, and 26 is insufficient, making them unsuitable for readers to view. It is recommended to replace them with images of higher resolution.
[Response3]：We recognize the concerns about the clarity of Figures 17, 24, and 26. In the revised manuscript, we have included high-resolution images to ensure that readers can easily view and comprehend the information.
Comment5：In Figures 19-21, a relatively large amount of space is used to show the transient changes in the flow field vortex system between the blade stages. It is recommended to supplement the theoretical explanations to support the pressure changes under different working conditions.
[Response5]：In Figures 19-21, we show the transient changes in the flow field vortex system between the blade stages. However, the theoretical explanation is insufficient. The following theoretical analyses can be added to supplement the explanation. We will revise it as follows for clarity and to highlight key points in the part of 3.4 Correlation between flow structures and pressure pulsation.
Under non-uniform inlet conditions, the flow at the impeller inlet is complex, featuring significant variations in both velocity and direction. These fluctuations result in unbalanced aerodynamic forces acting on the blades during rotation, leading to pressure fluctuations at the impeller outlet. For instance, when the left inlet serves as the primary air source, the left blades experience greater impact forces during rotation, which causes more pronounced pressure fluctuations on the left side of the impeller outlet. This observation aligns with the higher amplitude of low-frequency and broadband fluctuations noted near the monitoring points on the left side, as illustrated in Figures19-21. The asymmetric vortex structures also influence the pressure distribution. As demonstrated in Figure 21, the vortex structures within both the wide and narrow impellers display a striped distribution. The consistent strength and arrangement of these vortices contribute to relatively stable pressure fluctuations at the impeller outlet, characterized by a smaller amplitude of the pressure coefficient.
Comment6：What is "acum" in Figure 24, and it is recommended to supplement how it is specifically calculated.
[Response6]： "Acum" is a unit of measurement used to assess sharpness, which is a psychoacoustic metric that evaluates the perceived prominence of high-frequency components in sound. It quantifies the contribution of high-frequency signals to overall sound perception. Sharpness is calculated according to the DIN 45692:2009-08 standard. In this study, we analyze calculated sharpness values under different inlet conditions to evaluate the proportion of high-frequency components in the sound, thereby allowing us to understand the noise characteristics of the fan.
We had tried our best to improve the manuscript and made some changes according to the reviewer’s suggestions. We appreciate for Editors/Reviewers’ meticulous work earnestly and hope that the correction will meet with approval. Once again, thank you for your comments and suggestions.
Thank you and best regards.
Yours sincerely,
Yougen Huang on behalf of the authors.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors1. The numerical simulation section of the article only conducted flow field analysis and obtained velocity and pressure distribution. Suggest the author to convert the flow field results into sound field distribution and conduct comparative analysis in experimental testing.The following literature provides examples for your reference.DOI:10.1016/j.jngse.2016.01.021ï¼›10.2516/ogst/2019038ï¼› 10.1177/10775463221082754.
2. The establishment process of computational model should be introduced in detail, including the selection of computational domain, boundary conditions, Grid division，etc.
3. What principles should be followed for the structural improvement of wind turbines？
Author Response
[Comment1]：The numerical simulation section of the article only conducted flow field analysis and obtained velocity and pressure distribution. Suggest the author to convert the flow field results into sound field distribution and conduct comparative analysis in experimental testing. The following literature provides examples for your reference.
[Response1]:We appreciate the suggestion to convert flow field results into sound field distributions and conduct comparative experimental analyses. In the current study, our flow field analysis offers valuable insights into the internal flow characteristics of the centrifugal fan under various inlet conditions. However, to enhance the comprehensiveness and depth of our research, we plan to incorporate sound field analysis in future work. We will utilize relevant acoustic models and software tools to transform the flow field results from numerical simulations into sound field distribution data. This will facilitate a more detailed examination of the fan's noise characteristics. Furthermore, we intend to conduct experimental testing to measure the actual sound field distribution of the fan under different inlet conditions, enabling a direct comparison with the numerical simulation results. This comparative analysis will help validate the accuracy of the simulation model and provide a more reliable foundation for noise reduction design. We will refer to relevant literature to guide our work. we have made substantial revisions in the Introduction to strengthen this connection. Thank you for your understanding. Liu[27] Using large eddy simulation and acoustic analogy theory, the flow noise at a natural gas transmission and distribution station has been analyzed. A small hole muf-fler was designed to effectively reduce low-frequency noise by up to 37.4 dB, with an average noise reduction of approximately 20.9 dB.
[Comment2]：The establishment process of computational model should be introduced in detail, including the selection of computational domain, boundary conditions, Grid division，etc.
[Response2]:We completely agree with the suggestion to provide a more detailed introduction to the computational model establishment process. In the revised manuscript, we will elaborate on the following aspects:
Computational Domain Selection: The computational domain is defined based on the actual geometry of the asymmetric double-suction centrifugal fan and its surrounding environment. This domain includes the fan's inlet, impeller, volute, and outlet, ensuring that the entire flow path of the fluid is covered. The boundaries of the computational domain are set at a sufficient distance from the fan to minimize the impact of boundary conditions on the internal flow of the fan.
Boundary Condition Selection: Appropriate boundary conditions are crucial for ensuring the accuracy of the simulation results. For the inlet boundary, we adopt a pressure inlet condition, with the inlet pressure determined based on actual operating conditions. At the outlet boundary, we specify a mass flow outlet condition, with the mass flow rate set according to the design flow rate of the fan. The wall boundaries of the impeller and volute are assigned no-slip boundary conditions. Additionally, we specify the rotational speed of the impeller to simulate its actual operating state.
Grid Division: Grid division is a critical step in computational fluid dynamics (CFD) simulations. We use ANSYS ICEM software for grid generation. The impeller and volute regions are meshed using hexahedral elements, while the remaining areas are meshed with tetrahedral elements. To ensure the accuracy of the simulation results, we conduct a grid independence study. We numerically simulate seven different grid partitioning schemes. The grid count is gradually increased until the total pressure of the fan stabilizes, indicating that the grid is sufficiently refined. Ultimately, we select a grid count of 9.18×106 for the numerical simulation, providing a balance between computational efficiency and accuracy.
In the revised manuscript, we will explicitly present the control equations as follows:The basic governing equations consist of the continuity equation, momentum equation, and energy equation. In addition, the LES (Large - Eddy Simulation) turbulence model is selected. This turbulence model can derive the LES governing equations by adding a filtering function to the Navier - Stokes equations.
[Comment2]：What principles should be followed for the structural improvement of wind turbines？
[Response2]：In designing a fan system, it is essential not only to optimize the aerodynamic parameters of the fan for its intended operating conditions but also to ensure proper matching with the ductwork. This involves guaranteeing uniform airflow as it enters the fan. For asymmetric centrifugal fans, the conditions of the inlet flow significantly affect both the aerodynamic performance and noise levels of the fan. Poor inlet conditions or an improper match between the fan and ductwork can result in reduced operational efficiency, as well as increased noise and vibration. For example, the findings in this paper reveal that the area and velocity of the inlet on the rotating side must be appropriately matched, and the optimal combination of parameters should be determined.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThis paper studies a combination of performance testing and the large eddy simulation to analyze the impact of different inlet conditions on the performance curve, impeller outlet pressure pulsation, unsteady flow structures, and sound quality of an asymmetric double-suction centrifugal fan.
A non-uniform air distribution at the inlet is proposed to enhance the fan's aerodynamic and noise characteristics.
All figures are clearly given and good; but there are some issues must be considered：
[1]. in Fig. 9, how to define transient and steady? does Fig. 9 all pick from [36]?
[2]. in the paper, all methods used are not clearly given: theory, modeling, and so on
[3]. why time and frquency domains are both used?
Author Response
[Comment1]：in Fig. 9, how to define transient and steady? does Fig. 9 all pick from [36]?
[Response1]:In reference [36], the chosen simulation model aligns with the one used in this study, and a comparison between the simulation and experimental results is presented. we have made several key improvements in part of numerical method: As illustrated in the figure, the results from both the simulation and experiments show a strong correspondence in the high flow rate region. In the low flow rate area, the trends of both results are generally consistent, with the maximum error kept within 3%.
[Comment2]：in the paper, all methods used are not clearly given: theory, modeling, and so on
[Response2]: We sincerely apologize for the lack of clarity regarding the methods used in the paper. In the revised manuscript, we will provide a detailed introduction to the methods as follows:
Theoretical Basis: This study is based on the principles of fluid mechanics and aerodynamics, employing the Navier-Stokes equations to describe the flow field within the fan. We have chosen the large eddy simulation (LES) model to capture the complex unsteady flow phenomena occurring in the fan. This model effectively simulates large-scale eddies while accurately modeling small-scale eddies, providing a balance between computational accuracy and efficiency.
Modeling Process: The geometric model of the fan is created using CAD software, with dimensions and parameters derived from actual engineering requirements. The computational domain encompasses the entire flow path of the fluid in the fan, including the inlet, impeller, volute, and outlet. Meshing is performed using ANSYS ICEM software, with hexahedral elements used for the impeller and volute regions, while tetrahedral elements are employed for the remaining areas. A grid independence study is conducted to ensure the accuracy and reliability of the simulation results.
Numerical Simulation Method: The SST k-ω turbulence model is utilized for steady-state simulations to provide initial values for subsequent unsteady simulations. A sliding mesh model is employed to manage the dynamic interface between the impeller and other components, with the impeller being rotated by 0.5 degrees per step, corresponding to a time step of 6.9444×10-5 seconds. The SIMPLE algorithm is used to solve the pressure-velocity coupling, while the second-order upwind scheme is applied for spatial discretization. Convergence criteria for the simulations are established based on residual values and the stability of key monitoring parameters.
[Comment3]：why time and frquency domains are both used?
[Response3]: The use of both time domain and frequency domain analyses in this study serves several important purposes:
Time Domain Analysis: This analysis focuses on the time-varying characteristics of pressure signals at specific points. It directly reflects the instantaneous fluctuations in pressure and the stability of the flow field. By examining time-domain signals, we can identify the periodicity and amplitude of pressure fluctuations, which helps us understand the unsteady characteristics of the flow field and their impact on fan performance.
Frequency Domain Analysis: This analysis transforms time-domain signals into the frequency domain using the fast Fourier transform (FFT). This process allows us to identify the dominant frequency components and their corresponding amplitudes in the pressure pulsations. By studying frequency-domain signals, we can determine the excitation sources of different frequency components and their contributions to noise and vibration. This understanding provides a foundation for noise control and vibration reduction.
we have made several key improvements in part of Flow Field Analysis: Time-domain analysis offers a detailed description of the instantaneous characteristics of pressure signals, while frequency-domain analysis provides a deeper understanding of the frequency components and their sources. By combining both approaches, we gain a more comprehensive understanding of the fan's flow field characteristics and their relationship with noise and vibration.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsThis study utilizes a combination of performance testing and the large eddy simulation to analyze the impact of different inlet conditions on the performance curve, impeller outlet pressure pulsation, unsteady flow structures, and sound quality of an asymmetric double-suction centrifugal fan. This work has significance and is well-written. I recommend the publication after addressing the following comments.
1 The control equation system should be given for the LES simulation.
2. More efficient and CFD tools to improve the LES results should be mentioned. Such as
2023. A unified framework for non-linear reconstruction schemes in a compact stencil. Part 1: Beyond second order. Journal of Computational Physics, 481, p.112052.
2023. A new open-source library based on novel high-resolution structure-preserving convection schemes. Journal of Computational Science, 74, p.102150.
2023. An accurate and practical numerical solver for simulations of shock, vortices and turbulence interaction problems. Acta Astronautica, 210, pp.1-13.
The source code of the advanced tool is available at https://github.com/ROUNDschemes/libROUNDSchemes
Author Response
[Comment1]：The control equation system should be given for the LES simulation.
[Response1]：We sincerely apologize for the oversight in not providing the control equation system for the large eddy simulation (LES). In the revised manuscript, we will explicitly present the control equations as follows:
The basic governing equations consist of the continuity equation, momentum equation, and energy equation. In addition, the LES (Large - Eddy Simulation) turbulence model is selected. This turbulence model can derive the LES governing equations by adding a filtering function to the Navier - Stokes equations.
[Comment2]：More efficient and CFD tools to improve the LES results should be mentioned.
[Response2]：We appreciate the suggestion to mention more efficient and advanced CFD tools that could improve the LES results. Along with the methods used in this study, we would like to highlight several state-of-the-art CFD tools and advancements that have the potential to enhance the LES results.
we have made several key improvements in Introduction: Deng[28-30] mentioned more efficient and advanced CFD tools that could improve the LES results.
Author Response File: Author Response.pdf
Reviewer 5 Report
Comments and Suggestions for AuthorsPlease see the attached pdf.
Comments for author File: Comments.pdf
Author Response
[Comment1]：Figures 4 and 5 provide experimental results. However, statistical information regarding the experiments is missing, which is crucial to quantify precision and ensure repeatability of the experiments. For instance, howmany samples are taken for each case and the statistics of the sample in terms of mean variance, or standard deviation should be mentioned. This is specifically important because conclusions are drawn on the basis of these observations.
[Response1]：We sincerely appreciate the editor's valuable feedback. we have made several key improvements in part of Analysis of aerodynamic performance: The data is derived from aerodynamic performance tests. To ensure accuracy, we compared measurements taken at different times and with various fan products, maintaining a deviation in air volume measurement of no more than 1%. Data was collected while testing nine different inlet conditions at a constant fan speed. For each condition, we gathered 13 sets of data on air volume, static pressure, total pressure, and power by adjusting the nozzles. Using this information, we calculated the total pressure efficiency.
[Comment2]：During the CFD simulation, it is not clear how the rotation of the blades is captured The authors need to clarify whether a sliding mesh or an overset mesh is used. How is the information transfer between rotating and non-rotating mesh considered?
[Response2]：In the CFD simulations of this paper, the sliding mesh model is used to capture the blade rotation, facilitating data transfer between the rotating and non - rotating mesh regions.
[Comment3]：It is not clear why a certain fan rpm（1200)and a specific flow rate（12m3/min）were considered for this study. Please provide a justification for this. Will key the conclusions of the paper change if a different flow rate is considered?
[Response3]：IWe sincerely appreciate the editor's valuable feedback. we have made several key improvements in part of fan model:
In this study, a fan speed of 1200 rpm and a flow rate of 12 m³/min were chosen based on typical operating conditions for residential kitchen range hoods. These parameters represent common usage scenarios, ensuring that the results are applicable to real-world situations.
Additionally, the aerodynamic performance data for different speeds and flow rates are presented in Figures 4 and 5, highlighting the variations in aerodynamic impact. For subsequent simulations and to facilitate a comparable analysis, this study will use the working conditions of 1200 rpm and 12 m³/min for comparison.
Author Response File: Author Response.pdf
