Abstract

Purpose - This paper aims to propose a numerical method to calculate the convective heat transfer coefficient of spiral bevel gears under the condition of splash lubrication and to reveal the lubrication and temperature characteristics between the gears and the oil-air two-phase flow.Design/methodology/approach - Based on computational fluid dynamics, the multiple reference frames (MRF) method was used to simulate the rotational characteristics of gears and the motions of their surrounding fluid. The lubrication and temperature characteristics of gears were studied by combining the MRF method with the volume of the fluid multiphase flow model.Findings - The convective heat transfer coefficient can be improved by increasing the rotational speed and the oil immersion depth. Moreover, the temperature of the tooth surface having a large convective heat transfer coefficient is also found to be low. A large convection heat transfer coefficient could lead to a good cooling effect.Originality/value - This method can be used to obtain the convective heat transfer coefficient values at different meshing positions, different radii and different tooth surface positions. It also can provide research methods for improving the cooling effect of gears under the condition of splash lubrication.Peer review - The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2020-0233/


Authors

Lu, Fengxia;  Wang, Meng;  Liu, Weizhen;  Bao, Heyun;  Zhu, Rupeng

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  • 1 reviewer
  • pre-publication peer review (FINAL ROUND)
    Decision Letter
    2020/12/12

    12-Dec-2020

    Dear Lu, Fengxia; Wang, Meng; Liu, Weizhen; heyun, bao; Zhu, Rupeng

    It is a pleasure to accept your manuscript ilt-07-2020-0233.R3, entitled "CFD-based calculation method of convective heat transfer coefficient of spiral bevel gear in intermediate gearbox under splash lubrication" in its current form for publication in Industrial Lubrication and Tribology. Please note, no further changes can be made to your manuscript.

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    Prof. Carsten Gachot
    Editor, Industrial Lubrication and Tribology
    carsten.gachot@tuwien.ac.at

    Decision letter by
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    Reviewer report
    2020/12/12

    The authors have addressed the comments based on the previous review.

    Reviewed by
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    Author Response
    2020/11/12

    Response to editorial comments
    Comment 1: The manuscript does not contain any scientific discussion.
    Response 1: Thanks for your comment. Section “4 Lubrication and temperature characteristics” and Section “5 Results of different operating conditions” in the previous manuscript are actually scientific discussions. In order to express it more clearly, we have integrated these parts into the Section “4 Results and discussions”, and added relevant contents, such as “The temperature characteristic of gear is affected by the lubrication condition of gear tooth surface. However, it is difficult to measure the lubrication condition of gear tooth surface under splash lubrication.”, as shown in Section “4.2 Lubrication and temperature characteristics”, and “When the gear rotates, the oil is splashed along the tangent direction of the gear, some of which are splashed to the gear meshing area and some to the wall of the casing. The oil splashed to the meshing point is driven down or along the tangent line by gravity and centrifugal force to lubricate the tooth surface. As shown in Figure 6(a) and (b), the oil content is high near the meshing area (azimuth angle is 0°/360°). In the range of azimuth 180°–270°, the oil content of the driving gear tooth surface decreases obviously, because the centrifugal force of oil droplets is greater than that of gravity. For the same reason, in the range of azimuth 135°–225°, the oil content of the driven gear tooth surface decreases obviously. Moreover, because the gap between the driven gear and the casing is small at azimuth of 270°, the oil on the casing wall is hindered when it falls here, and the oil droplets accumulate on the tooth surface, so the oil content of the driven gear tooth surface with azimuth angle of 270° rises.”, as shown in Section “4.2.1 Lubrication characteristics”.
    Comment 2: References are really not up-to-date.
    Response 2: Thanks for your comment. We have added three references on the calculation of heat transfer coefficient in 2020 in the introduction.
    We have improved both aspects.



    Cite this author response
  • pre-publication peer review (ROUND 3)
    Decision Letter
    2020/11/08

    08-Nov-2020

    Dear Dr. Lu:

    Manuscript ID ilt-07-2020-0233.R2 entitled "CFD-based calculation method of convective heat transfer coefficient of spiral bevel gear in intermediate gearbox under splash lubrication" which you submitted to the Industrial Lubrication and Tribology, has been reviewed. The comments of the reviewer(s) are included at the bottom of this letter.

    The reviewer(s) have recommended major revisions to the submitted manuscript, before it can be considered for publication. Therefore, I invite you to respond to the reviewer(s)' comments and revise your manuscript.

    To revise your manuscript, log into https://mc.manuscriptcentral.com/ilt and enter your Author Centre, where you will find your manuscript title listed under "Manuscripts with Decisions." Under "Actions," click on "Create a Revision." Your manuscript number has been appended to denote a revision.

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    Once again, thank you for submitting your manuscript to the Industrial Lubrication and Tribology and I look forward to receiving your revision.

    Sincerely,
    Prof. Carsten Gachot
    Editor, Industrial Lubrication and Tribology
    carsten.gachot@tuwien.ac.at

    Editorial comments.

    The manuscript does not contain any scientific discussion.

    References are really not up-to-date.

    Please improve both aspects.

    Reviewer(s)' Comments to Author:
    Reviewer: 1

    Comments to the Author
    The manuscript was modified based on the suggestions. Therefore, I suggest it be published.

    Reviewer: 2

    Comments to the Author
    Suggest to accept itfor publication.
    Reviewer: 1

    Recommendation: Accept

    Comments:
    The manuscript was modified based on the suggestions. Therefore, I suggest it be published.

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: Yes

    Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: Yes

    Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: Yes

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: Yes

    Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: Yes

    Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: Yes

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?:

    This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no. All peer review content displayed here will be covered by a Creative Commons CC BY 4.0 license.: Yes, I would like my name to appear with my report on Publons

    Reviewer: 2

    Recommendation: Accept

    Comments:
    Suggest to accept itfor publication.

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: yes

    Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: yes

    Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: yes

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: yes

    Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: yes

    Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: yes

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?:

    This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no. All peer review content displayed here will be covered by a Creative Commons CC BY 4.0 license.: No, I would not like my name to appear with my report on Publons

    Decision letter by
    Cite this decision letter
    Reviewer report
    2020/11/08

    Suggest to accept itfor publication.

    Reviewed by
    Cite this review
    Reviewer report
    2020/10/10

    The manuscript was modified based on the suggestions. Therefore, I suggest it be published.

    Reviewed by
    Cite this review
    Author Response
    2020/09/30

    Reviewer: 1
    2. Model of intermediate gearbox
    Comment 1: Please added the R=εσAT^4 explanation into the manuscript.
    Response 1: Thanks for your comment. The R=εσAT^4 explanation has been added into the manuscript.
    3.4 Boundary conditions
    Comment 2: Please list the hardness of gear and casing.
    Response 2: Thanks for your comment. The hardness of gear and casing has been listed in Table III. The hardness of gear was HRA 81–83, and the hardness of casing was HBS 100.
    5. Results of different operating conditions
    Comment 3: Is there any possibility the microstructure of gear and casing will be changed when the temperature goes up? If not, please explain.
    Response 3: Thanks for your comment. There is a possibility the microstructure of gear and casing will be changed when the temperature goes up. However, due to the following reasons, the microstructure changes can be ignored under the normal lubrication conditions of the intermediate gearbox.
    (1) During the normal operation of the intermediate gearbox, the lubricating oil supply is sufficient. The gear is in the state of fluid lubrication. The friction surface is separated by a continuous lubricant film. The gear tooth surface will not be scratched or glued, and wear is small. Compared with the plastic deformation in the dry friction stage, the microstructure change of gear can be ignored.
    (2) The surface of gear in the intermediate gearbox has been shot peened, and the tooth surface has a high finish. The gear still has a low friction coefficient even under the condition of no oil lubrication, and the gear microstructure changes little.
    (3) The casing was made of cast aluminum alloy with high thermal strength and small expansion coefficient. The casing has sufficient heat carrying capacity and rigidity, and the microstructure of the casing surface changes little when the temperature goes up.
    (4) Under sufficient lubrication, the temperature rise of gear and casing is small (generally 60℃–70℃), which will not cause excessive morphological changes.



    Cite this author response
  • pre-publication peer review (ROUND 2)
    Decision Letter
    2020/09/27

    27-Sep-2020

    Dear Dr. Lu:

    Manuscript ID ilt-07-2020-0233.R1 entitled "CFD-based calculation method of convective heat transfer coefficient of spiral bevel gear in intermediate gearbox under splash lubrication" which you submitted to the Industrial Lubrication and Tribology, has been reviewed. The comments of the reviewer(s) are included at the bottom of this letter.

    The reviewer(s) have recommended revisions to the submitted manuscript, before it can be considered for publication. Therefore, I invite you to respond to the reviewer(s)' comments and revise your manuscript.

    To revise your manuscript, log into https://mc.manuscriptcentral.com/ilt and enter your Author Centre, where you will find your manuscript title listed under "Manuscripts with Decisions." Under "Actions," click on "Create a Revision." Your manuscript number has been appended to denote a revision.

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    Once the revised manuscript is prepared, you can upload it and submit it through your Author Centre. The deadline for uploading a revised manuscript is 27-Oct-2020 from receiving this email. If it is not possible for you to resubmit your revision within this timeframe, we may have to consider your paper as a new submission.

    When submitting your revised manuscript, you will be able to respond to the comments made by the reviewer(s) in the space provided. You can use this space to document any changes you make to the original manuscript. In order to expedite the processing of the revised manuscript, please be as specific as possible in your response to the reviewer(s).

    IMPORTANT: Your original files are available to you when you upload your revised manuscript. Please delete any redundant files before completing the submission.

    Please note that Emerald requires you to clear permission to re-use any material not created by you. If there are permissions outstanding, please send these to Emerald as soon as possible. Emerald is unable to publish your paper with permissions outstanding.

    To help support you on your publishing journey we have partnered with Editage, a leading global science communication platform, to offer expert editorial support including language editing and translation.
    If your article has been rejected or revisions have been requested, you may benefit from Editage’s services. For a full list of services, visit: authorservices.emeraldpublishing.com/
    Please note that there is no obligation to use Editage and using this service does not guarantee publication.

    Once again, thank you for submitting your manuscript to the Industrial Lubrication and Tribology and I look forward to receiving your revision.

    Sincerely,
    Prof. Carsten Gachot
    Editor, Industrial Lubrication and Tribology
    carsten.gachot@tuwien.ac.at

    Editorial note:

    Please consider the latest review of the group of Profito at el related to CFD modeling.

    Reviewer(s)' Comments to Author:
    Reviewer: 1

    Comments to the Author
    2. Model of intermediate gearbox
    1. Please added the R=εσAT^4 explanation into the manuscript.
    3.4 Boundary conditions
    1. Please list the hardness of gear and casing.
    5. Results of different operating conditions
    1. Is there any possibility the microstructure of gear and casing will be changed when the temperature goes up? If not, please explain.

    Reviewer: 2

    Comments to the Author
    This paper focused on a numerical method to calculate the convective heat transfer coefficient of spiral bevel gears under splash lubrication, and to reveal the lubrication and temperature characteristics between gears and oil-air two-phase flow. Suggest to accept it for publication.
    Reviewer: 1

    Recommendation: Minor Revision

    Comments:
    2. Model of intermediate gearbox
    1. Please added the R=εσAT^4 explanation into the manuscript.
    3.4 Boundary conditions
    1. Please list the hardness of gear and casing.
    5. Results of different operating conditions
    1. Is there any possibility the microstructure of gear and casing will be changed when the temperature goes up? If not, please explain.

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: Yes, but it still needs to improve at some point.

    Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: If provide the relevant experimental tests would be better.

    Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: Yes, but it needs more details.

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: Yes, but the authors need to consider more factors effect.

    Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: If provide the relevant experimental tests would be better.

    Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: Yes

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?:

    This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no. All peer review content displayed here will be covered by a Creative Commons CC BY 4.0 license.: Yes, I would like my name to appear with my report on Publons

    Reviewer: 2

    Recommendation: Accept

    Comments:
    This paper focused on a numerical method to calculate the convective heat transfer coefficient of spiral bevel gears under splash lubrication, and to reveal the lubrication and temperature characteristics between gears and oil-air two-phase flow. Suggest to accept it for publication.

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: Yes

    Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: Yes.

    Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: Yes

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: Yes

    Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: Yes

    Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: some

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?:

    This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no. All peer review content displayed here will be covered by a Creative Commons CC BY 4.0 license.: No, I would not like my name to appear with my report on Publons

    Decision letter by
    Cite this decision letter
    Reviewer report
    2020/09/26

    This paper focused on a numerical method to calculate the convective heat transfer coefficient of spiral bevel gears under splash lubrication, and to reveal the lubrication and temperature characteristics between gears and oil-air two-phase flow. Suggest to accept it for publication.

    Reviewed by
    Cite this review
    Reviewer report
    2020/08/31

    1. Model of intermediate gearbox
    2. Please added the R=εσAT^4 explanation into the manuscript.
      3.4 Boundary conditions
    3. Please list the hardness of gear and casing.
    4. Results of different operating conditions
    5. Is there any possibility the microstructure of gear and casing will be changed when the temperature goes up? If not, please explain.

    Reviewed by
    Cite this review
    Author Response
    2020/08/16

    Reviewer: 1
    This paper focused on a numerical method to calculate the convective heat transfer coefficient of spiral bevel gears under splash lubrication, and to reveal the lubrication and temperature characteristics between gears and oil-air two-phase flow. The reviewer read this paper with great interest. Although the presented work is meaningful, there are some issues which should be more clearly clarified or addressed:
    Comment 1: The meaning about ‘simulation based calculation method’ onto convective heat transfer coefficient should be considered to improve the title of the manuscript.
    Response 1: Thanks for your comment. We have improved the title of the manuscript to: ‘CFD-based calculation method of convective heat transfer coefficient of spiral bevel gear in intermediate gearbox under splash lubrication’.
    Comment 2: The physical parameters concerned for this simulation should be described in details.
    Response 2: Thanks for your comment. We have added more description about physical parameters concerned for this simulation in the manuscript. For example, information such as mesh, numerical model, boundary conditions, heat source calculation method, oil type, oil properties, solid material and its properties have been described in details.
    Comment 3: More details of the numerical model should be introduced. How many nodes/elements are there in the model, and how many nodes/elements are there in its solid model and its fluid model, respectively? How to determine the mesh’s density? How are they coupled between the oil and air, between the solid and the oil/air? Are there any constraints applied on the gears?
    Response 3: Thanks for your comment. More details of the numerical model have been introduced. As follows:
    (1) The model had 148874 nodes and 690682 elements in its solid model and 248328 nodes and 1145469 elements in its fluid model. The solid and the fluid models were coupled by node sharing. Therefore, in total, there were 317961 mesh nodes and 1836151 mesh elements in the model.
    (2) By analyzing the mesh independence, it can be concluded that when the number of mesh elements was between 1800000 and 2500000, the flow rate change of the air vent was controlled within 2%. Therefore, selecting a mesh density of approximately 1800000 mesh elements can sufficiently achieve the desired calculation accuracy without wasting computational resources.
    (3) The solid and the fluid (oil/air) are coupled by node sharing. The fluid domain is composed of oil and air. The oil content was controlled by patch operation, and the volume of fluid (VOF) model was used to track the oil-air interface. The VOF model can automatically track the interface between oil and air without coupling.
    (4) The equations of motion of the driving gear and driven gear were converted into rotational domains 1 and 2, respectively, and solved. The rotational speeds of rotational domains 1 and 2 were set to 5000 r/min and 3804 r/min, respectively, which were equal to the rotational speeds of the driving gear and the driven gear. The constraints applied to the gears were that the walls of driving and driven gears were relatively static with rotational domains 1 and 2, respectively.
    Comment 4: Suggest to introduce the calculation method about heat sources of driving and driven gears.
    Response 4: Thanks for your comment. The calculation method about heat sources of diving and driven gears has been added, as shown in Section “3.4 Boundary conditions”.
    Comment 5: It is claimed that “As shown in Figure 7(c)(d), the temperature is the highest near the meshing surface,……”, Suggest to check its correctness.
    Response 5: Thanks for your comment. The sentence has been checked and corrected. “As shown in Figure 6(c) and (d), the temperature is high near the meshing area, in particular, when the azimuth angle is in the range of 0°–90° or 270°–360°……”.
    Comment 6: It is concluded that “(1) The MRF model can better simulate the rotation characteristic of gear and the movement of the surrounding fluid,……” Are there any data to support this conclusion?
    Response 6: Thanks for your comment. We have claimed in the manuscript that “It took approximately 48 h to achieve convergence using a computer with 48 CPUs. Therefore, the MRF model can reduce the time required by the CFD method to calculate the temperature fields.” In terms of the calculation time, the MRF model can better simulate the rotation characteristic of gear and the movement of the surrounding fluid. However, for more accuracy, it was changed by “(1) The MRF model was used to simulate the rotational characteristics of gear and the movement of the surrounding fluid.”
    Comment 7: The experimental method should be adopted to verify the conclusions from the simulation analysis in this paper.
    Response 7: Thanks for your comment. We have completed the flow field and temperature experiments of the intermediate gearbox. Due to the difficulty of measuring the convective heat transfer coefficient, an effective measurement method has not yet been formed, so the experiment of measuring the gear convective heat transfer coefficient has not been carried out. However, the parameters added when running the CFD was completely set in accordance with the real operating conditions of the intermediate gearbox, including rotational speed, input power, solid material properties, oil properties and oil content, etc. It is also mentioned at the end of the paper: “In the future, the experimental measurement and error analysis of the convective heat transfer coefficient of gears will be studied in detail.”
    Comment 8: Suggest to check the correctness of references listed and those cited in the manuscript, including the abbreviation of the authors etc.
    Response 8: Thanks for your comment. The correctness of references listed and those cited in the manuscript, including the abbreviation of the authors has been checked and corrected. The references have been checked for conformance with journal guidelines. Furthermore, they have been arranged in alphabetical order as required.
    Comment 9: There are some English grammar mistakes in the manuscript. Its English writing needs improvement.
    Response 9: Thanks for your comment. We have corrected the English grammar mistakes in the manuscript and improved the English writing through the Editage’s services. We would like to thank Editage (www.editage.com) for English language editing.

    Reviewer: 2
    1.Introduction
    Comment 1: Please add more literature review about the gear coefficient under splash lubrication.
    Response 1: Thanks for your comment. In the paper, we have made some literature review about the calculation of convective heat transfer coefficient. However, previous studies have mainly focused on the oil injection lubrication, and studies on calculating the gear coefficient under splash lubrication conditions are few. Furthermore, after re-searching the literature, it was found that there is no more published literature on the gear coefficient under splash lubrication. On this basis, a method is proposed to calculate the convective heat transfer coefficient of gears under splash lubrication conditions in this manuscript.
    2. Model of intermediate gearbox
    Comment 2: Make the oil distribution in Figure1.
    Response 2: Thanks for your comment. The oil distribution has been made in Figure1.
    Comment 3: “Because the effect of heat radiation is small, it is ignored in this paper.” Please describe how small it is.
    Response 3: Thanks for your comment. The Stefen-Boltzmann empirical correction calculation formula is used to calculate radiation heat flux of the object:
    R=εσAT^4
    where R is the radiation heat flux; ε is the emissivity; σ is the Stefen-Boltzmann constant, taken as 5.67×10^-8; A is the radiation surface area; T is the thermodynamic temperature.
    The casing of the intermediate gearbox was made of cast aluminum alloy, and ε is 0.2. The radiation heat flux is about 0.06 kW. It should be noted that the calculation result is the heat flux radiated by the object itself, which does not change with the environmental conditions. However, to calculate the radiant heat flux between the object and the surrounding object with temperature difference, the absorption process of radiant heat projected onto the object must also be considered. Since the temperature difference among the internal parts of the intermediate gearbox is small, heat loss due to radiation is negligible.
    3.4 Boundary conditions
    Comment 4: Please provide the type of oil, and describe the oil properties. Have authors considered the temperature effect on the properties of oil?
    Response 4: Thanks for your comment. NATO O-155 oil was used, and the temperature effect on the oil properties was also considered (Table II).
    Comment 5: What is the exact material of the simulation? Provide the properties as well.
    Response 5: Thanks for your comment. The gear was made of alloy steel, and the casing was made of cast aluminum alloy. The properties of the solid materials are shown in Table III.
    Comment 6: Have the authors considered the surface roughness, surface texture?
    Response 6: No. We haven’t considered the surface roughness, surface texture. We mainly focused on the convective heat transfer coefficient between oil-air two-phase flow caused by gear splashing. Here, the macroscopic flow state of oil was considered, and the influence of microscopic parameters such as the surface roughness and surface texture was not paid attention to. Thanks for the reviewer’s comment, we will carry out research on the influence of surface roughness and surface texture on gear convective heat transfer coefficient in the future.
    5. Results of different operating conditions
    Comment 7: Have the authors tried to run the experimental tests? If so, please provide the experimental results. If not, how do authors added the parameters when running the CFD.
    Response 7: Thanks for your comment. We have completed the flow field and temperature experiments of the intermediate gearbox. Due to the difficulty of measuring the convective heat transfer coefficient, an effective measurement method has not yet been formed, so the experiment of measuring the gear convective heat transfer coefficient has not been carried out. However, the parameters added when running the CFD was completely set in accordance with the real operating conditions of the intermediate gearbox, including rotational speed, input power, solid material properties, oil properties and oil content, etc. It is also mentioned at the end of the paper: “In the future, the experimental measurement and error analysis of the convective heat transfer coefficient of gears will be studied in detail.”



    Cite this author response
  • pre-publication peer review (ROUND 1)
    Reviewer report
    2020/08/01

    1.Introduction
    1. Please add more literature review about the gear coefficient under splash lubrication.
    2. Model of intermediate gearbox
    1. Make the oil distribution in Figure1.
    2. "Because the effect of heat radiation is small, it is ignored in this paper." Please describe how small it is.
    3.4 Boundary conditions
    1. Please provide the type of oil, and describe the oil properties. Have authors considered the temperature effect on the properties of oil?
    2. What is the exact material of the simulation? Provide the properties as well.
    3. Have the authors considered the surface roughness, surface texture?
    5. Results of different operating conditions
    1. Have the authors tried to run the experimental tests? If so, please provide the experimental results. If not, how do authors added the parameters when running the CFD.

    Reviewed by
    Cite this review
    Decision Letter
    2020/07/31

    31-Jul-2020

    Dear Dr. Lu:

    Manuscript ID ilt-07-2020-0233 entitled "Convective heat transfer coefficient of spiral bevel gear in intermediate gearbox under splash lubrication" which you submitted to the Industrial Lubrication and Tribology, has been reviewed. The comments of the reviewer(s) are included at the bottom of this letter.

    The reviewer(s) have recommended major revisions to the submitted manuscript, before it can be considered for publication. Therefore, I invite you to respond to the reviewer(s)' comments and revise your manuscript.

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    Once again, thank you for submitting your manuscript to the Industrial Lubrication and Tribology and I look forward to receiving your revision.

    Sincerely,
    Prof. Carsten Gachot
    Editor, Industrial Lubrication and Tribology
    carsten.gachot@tuwien.ac.at

    Reviewer(s)' Comments to Author:
    Reviewer: 1

    Comments to the Author
    This paper focused on a numerical method to calculate the convective heat transfer coefficient of spiral bevel gears under splash lubrication, and to reveal the lubrication and temperature characteristics between gears and oil-air two-phase flow. The reviewer read this paper with great interest. Although the presented work is meaningful, there are some issues which should be more clearly clarified or addressed:
    1) The meaning about ‘simulation based calculation method’ onto convective heat transfer coefficient should be considered to improve the title of the manuscript.
    2) The physical parameters concerned for this simulation should be described in details.
    3) More details of the numerical model should be introduced. How many nodes/elements are there in the model, and how many nodes/elements are there in its solid model and its fluid model, respectively? How to determine the mesh’s density? How are they coupled between the oil and air, between the solid and the oil/air? Are there any constraints applied on the gears?
    4) Suggest to introduce the calculation method about heat sources of driving and driven gears.
    5) It is claimed that “As shown in Figure 7(c)(d), the temperature is the highest near the meshing surface,……”, Suggest to check its correctness.
    6) It is concluded that “(1) The MRF model can better simulate the rotation characteristic of gear and the movement of the surrounding fluid,……” Are there any data to support this conclusion?
    7) The experimental method should be adopted to verify the conclusions from the simulation analysis in this paper.
    8) Suggest to check the correctness of references listed and those cited in the manuscript, including the abbreviation of the authors etc.
    9) There are some English grammar mistakes in the manuscript. Its English writing needs improvement.

    Reviewer: 2

    Comments to the Author
    1.Introduction
    1. Please add more literature review about the gear coefficient under splash lubrication.
    2. Model of intermediate gearbox
    1. Make the oil distribution in Figure1.
    2. "Because the effect of heat radiation is small, it is ignored in this paper." Please describe how small it is.
    3.4 Boundary conditions
    1. Please provide the type of oil, and describe the oil properties. Have authors considered the temperature effect on the properties of oil?
    2. What is the exact material of the simulation? Provide the properties as well.
    3. Have the authors considered the surface roughness, surface texture?
    5. Results of different operating conditions
    1. Have the authors tried to run the experimental tests? If so, please provide the experimental results. If not, how do authors added the parameters when running the CFD.
    Reviewer: 1

    Recommendation: Major Revision

    Comments:
    This paper focused on a numerical method to calculate the convective heat transfer coefficient of spiral bevel gears under splash lubrication, and to reveal the lubrication and temperature characteristics between gears and oil-air two-phase flow. The reviewer read this paper with great interest. Although the presented work is meaningful, there are some issues which should be more clearly clarified or addressed:
    1) The meaning about ‘simulation based calculation method’ onto convective heat transfer coefficient should be considered to improve the title of the manuscript.
    2) The physical parameters concerned for this simulation should be described in details.
    3) More details of the numerical model should be introduced. How many nodes/elements are there in the model, and how many nodes/elements are there in its solid model and its fluid model, respectively? How to determine the mesh’s density? How are they coupled between the oil and air, between the solid and the oil/air? Are there any constraints applied on the gears?
    4) Suggest to introduce the calculation method about heat sources of driving and driven gears.
    5) It is claimed that “As shown in Figure 7(c)(d), the temperature is the highest near the meshing surface,……”, Suggest to check its correctness.
    6) It is concluded that “(1) The MRF model can better simulate the rotation characteristic of gear and the movement of the surrounding fluid,……” Are there any data to support this conclusion?
    7) The experimental method should be adopted to verify the conclusions from the simulation analysis in this paper.
    8) Suggest to check the correctness of references listed and those cited in the manuscript, including the abbreviation of the authors etc.
    9) There are some English grammar mistakes in the manuscript. Its English writing needs improvement.

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: no

    Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: some

    Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: The numerical model is not clearly introduced.

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: not clearly

    Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: some

    Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: not

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?:

    This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no. All peer review content displayed here will be covered by a Creative Commons CC BY 4.0 license.: No, I would not like my name to appear with my report on Publons

    Reviewer: 2

    Recommendation: Major Revision

    Comments:
    1.Introduction
    1. Please add more literature review about the gear coefficient under splash lubrication.
    2. Model of intermediate gearbox
    1. Make the oil distribution in Figure1.
    2. "Because the effect of heat radiation is small, it is ignored in this paper." Please describe how small it is.
    3.4 Boundary conditions
    1. Please provide the type of oil, and describe the oil properties. Have authors considered the temperature effect on the properties of oil?
    2. What is the exact material of the simulation? Provide the properties as well.
    3. Have the authors considered the surface roughness, surface texture?
    5. Results of different operating conditions
    1. Have the authors tried to run the experimental tests? If so, please provide the experimental results. If not, how do authors added the parameters when running the CFD.

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: Yes, but it needs to add the experimental data.

    Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: It needs to add more literature review about the splash lubrication.

    Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: Yes.

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: More information needs to be added.

    Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: More information needs to be added.

    Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: Yes.

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?: The numbers need to be added to the references. Otherwise, it not clear.

    This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no. All peer review content displayed here will be covered by a Creative Commons CC BY 4.0 license.: Yes, I would like my name to appear with my report on Publons

    Decision letter by
    Cite this decision letter
    Reviewer report
    2020/07/26

    This paper focused on a numerical method to calculate the convective heat transfer coefficient of spiral bevel gears under splash lubrication, and to reveal the lubrication and temperature characteristics between gears and oil-air two-phase flow. The reviewer read this paper with great interest. Although the presented work is meaningful, there are some issues which should be more clearly clarified or addressed:
    1) The meaning about ‘simulation based calculation method’ onto convective heat transfer coefficient should be considered to improve the title of the manuscript.
    2) The physical parameters concerned for this simulation should be described in details.
    3) More details of the numerical model should be introduced. How many nodes/elements are there in the model, and how many nodes/elements are there in its solid model and its fluid model, respectively? How to determine the mesh’s density? How are they coupled between the oil and air, between the solid and the oil/air? Are there any constraints applied on the gears?
    4) Suggest to introduce the calculation method about heat sources of driving and driven gears.
    5) It is claimed that “As shown in Figure 7(c)(d), the temperature is the highest near the meshing surface,……”, Suggest to check its correctness.
    6) It is concluded that “(1) The MRF model can better simulate the rotation characteristic of gear and the movement of the surrounding fluid,……” Are there any data to support this conclusion?
    7) The experimental method should be adopted to verify the conclusions from the simulation analysis in this paper.
    8) Suggest to check the correctness of references listed and those cited in the manuscript, including the abbreviation of the authors etc.
    9) There are some English grammar mistakes in the manuscript. Its English writing needs improvement.

    Reviewed by
    Cite this review
All peer review content displayed here is covered by a Creative Commons CC BY 4.0 license.