Performance Analysis of the Cylinder Gas Film Seal between Dual-Rotor Reverse Shafts Considering Lubrication and Centrifugal Expansion Effects
Round 1
Reviewer 1 Report
Comments to the Author
This article presents method for calculating the dynamic pressure, gas film force and friction power consumption with or without the inlet pressure difference for cylinder gas film seal between dual-rotor reverse shafts. Authors carried out theoretical analysis for four rotating modes and have shown that dynamic pressure effect is the weakest and the gas film force is minimal for 3th mode where inner and outer rotors are in counter-rotation. But, authors conclude that with inlet differential pressure of 80kPa gas film force can be increased by 68.1% for reverse direction mode. The paper is well organized with simple and clear language. I have only one suggestion for improvement and recommend a minor revision.
References are not cited properly, they should be corrected on entire list.
Reference 1, for example, should be written as:
1. He, Q.; Huang, W.; Hu, G. Development of aeroengine gas film seal technology. Aircraft Engine 2021, 47(04), 106-113.
Author Response
Point 1: This article presents method for calculating the dynamic pressure, gas film force and friction power consumption with or without the inlet pressure difference for cylinder gas film seal between dual-rotor reverse shafts. Authors carried out theoretical analysis for four rotating modes and have shown that dynamic pressure effect is the weakest and the gas film force is minimal for 3th mode where inner and outer rotors are in counter-rotation. But, authors conclude that with inlet differential pressure of 80kPa gas film force can be increased by 68.1% for reverse direction mode. The paper is well organized with simple and clear language. I have only one suggestion for improvement and recommend a minor revision.
References are not cited properly, they should be corrected on entire list.
Reference 1, for example, should be written as:
- He, Q.; Huang, W.; Hu, G. Development of aeroengine gas film seal technology. Aircraft Engine2021, 47(04), 106-113.
Response 1: Thank you very much for your valuable comments. The mistakes you pointed out are very correct. Due to the author's negligence, the document format was not correctly quoted according to the requirements of the press. Now the article has been changed according to your requirements. Thank you again for your criticism and correction.
For your question of "authors include that with inlet differential pressure of 80kPa gas film force can be increased by 68.1% for reverse direction mode", the following explanation is made: In the rotation mode 3, the relative rotational speed of the fluid is the smallest (compared with the other three rotation modes in the article), the dynamic pressure effect is the weakest, and the gas film force is the smallest. Therefore, the gas film force is the most affected by the inlet pressure difference, which is significantly higher than the other three rotation modes, and can increase by 68.1% under the 80kPa inlet pressure difference.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This paper presents an analytical study on the effect of running parameters (inner and outer ring speed and inlet pressure difference) on the performances of the cylinder gas film seal separating the reverse shafts rotating at high speed simultaneously.
The subject of the paper is very important, but some aspects have to be clarified before recommending this paper for publication.
1. The authors omitted to cite a recently published paper:
Hou G, Su H, Chen G. An analysis method for the performance of compliant cylindrical intershaft gas film seal considering centrifugal expansion effect. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science. 2022;236(6):2728-2739. doi:10.1177/09544062211035419
The novelty of the current research should be assessed in relationship with this omitted paper, as the conclusions seem the same.
2. The temperature in aircraft engines is not the ambient temperature, as supposed in this research. The thermal expansion of the elements cannot be neglected. The simplifying assumptions should be mentioned in the paper. A discussion about the effect of the temperature on the obtained results is recommended.
3. The adopted values for the comprehensive surface roughness and the ideal radius of the rough peak are not specified.
Author Response
Point 1: The authors omitted to cite a recently published paper:
Hou G, Su H, Chen G. An analysis method for the performance of compliant cylindrical intershaft gas film seal considering centrifugal expansion effect. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science. 2022;236(6):2728-2739. doi:10.1177/09544062211035419
The novelty of the current research should be assessed in relationship with this omitted paper, as the conclusions seem the same.
Response 1: Thank you very much for your valuable comments on this article. Your suggestions are very correct. Due to the author's negligence, I did not quote the paper you mentioned, which caused your misunderstanding in reading. I am deeply sorry for this. However, the paper you mentioned does not conflict with the innovation of this article. Now the paper you mentioned is supplemented in red font in Part 1 of the article, and its serial number is expressed as [11] (The supplementary content is “Hou [11] et al. on the base of the aeroelastic coupling method，Considering the influence of centrifugal expansion, the influence of centrifugal expansion, eccentricity and inner/outer rotor speed on sealing performance is investigated.”). The theoretical model, calculation method and research content are described as follows:
(1) Theoretical model: The theoretical model of this paper is quite different from the theoretical model of literature research. The cylindrical seal model with elastic foil is used in the literature. The seal ring and the outer rotor are not fixedly connected. The floating of the seal ring is realized by the elasticity of the elastic foil. The theoretical model in this paper is that the seal ring and the seal seat are connected by anti-rotation pins, which ensures that the speed of the seal ring and the outer rotor are the same. At the same time, because a certain radial distance is reserved between the seal seat and the seal ring, it ensures that the seal ring will not collide with the seal seat while floating, and has stronger stability and working life.
(2) Calculation method: The calculation method in this paper is essentially different from that in the literature. Although the influence of centrifugal expansion is considered in both papers, all calculations and analyses in the literature are based on the generally simplified Reynolds equation, and the average Reynolds equation is used in this paper, which makes the calculation results in this paper can consider the influence of surface roughness, thus making the calculation results in this paper more practical.
(3) Research content: The research content of this paper is quite different from the literature. Firstly, the working conditions of the sealing ring are different, and the influence of the inlet pressure change is not considered in the literature, but the influence of different rotation modes on the sealing performance is only considered; Based on the different rotation modes in the literature, the influence of inlet pressure difference on the sealing performance is deeply explored in this paper. Secondly, for the discussion of the influence of the rotating speed of the seal ring, the literature only discusses the two rotating modes of the same direction and the opposite direction, while this paper not only discusses the two discussion modes described in the literature, but also considers the influence of the other three rotating modes (The fixed speed of the inner rotor and the speed of the outer rotor change, The fixed speed of the outer rotor and the speed change of the inner rotor, The speed difference between internal and external rotors is certain) on the sealing performance, This makes the research content of this paper more consistent with the working conditions of the aeroengine, and also more sufficient. Finally, the research content of this paper is more rich in the calculation index of sealing performance. The literature only considers the leakage rate, and this paper also considers the friction power consumption on the basis of considering the leakage rate, which also makes the research content of this paper have more important guiding significance for engineering practice.
Thank you again for your criticism and correction!
Point 2: The temperature in aircraft engines is not the ambient temperature, as supposed in this research. The thermal expansion of the elements cannot be neglected. The simplifying assumptions should be mentioned in the paper. A discussion about the effect of the temperature on the obtained results is recommended.
Response 2: Thank you very much for your valuable comments on this article. Your suggestions are very correct and of great significance. As you pointed out, the ambient temperature in the engine is not normal temperature. Due to the limited level of the author, some details are not clearly stated, which has caused your misunderstanding in reading. I am deeply sorry for this. Temperature does have an important influence on centrifugal expansion. As the first part of the research on the cylindrical gas film seal between shafts, this paper first studies the influence of motion change on performance. The next step is to carry out the study of temperature effect(as you have said). The ambient temperature considered in the calculation results of this article is the real temperature in the engine, but due to the author's negligence, it was not expressed in the article, which caused your misunderstanding in reading. I am deeply sorry for this, changes have been made in red font in the article table 1 (Replace “ambient temperature” with “Operation temperature”, and the selected value is 930K). Thank you again for your criticism and correction!
Point 3: The adopted values for the comprehensive surface roughness and the ideal radius of the rough peak are not specified.
Response 3: Thank you very much for your valuable comments on the inadequacy of the article. Due to the author's negligence, the comprehensive surface roughness and the ideal radius of the rough peak were omitted, it has been supplemented in article 4.1.4 and marked in red font, values are 0.8 and 1.2 respectively. Thank you again for your valuable comments!
Author Response File: Author Response.docx
Reviewer 3 Report
This paper demonstrates a method for determining if the sealing ring is fully fluid-lubricated using the Reynolds equation. In the manuscript, the method used is unclear. Below are my comments;
1. How the authors calculate the thickness of the film is missing. The authors just show the film thickness equation without relating it to the pressure
2. How do the authors ensure that the lubricant momentum is conserved? In the manuscript, the corresponding equations are missing.
3. As stated in the paper, hydrodynamic lubrication will convert to a mixed lubrication regime when the lubricant fails to prevent contact. However, the equation for calculating the lubricants in such a regime is missing. Please elaborate in detail.
4. As claimed by the authors, surface texturing is taken into account. However, I do not find the description of the texture, such as the shape, the dimensions, and the film thickness of the lubricant as a function of the surface texture profile
Author Response
Point 1: How the authors calculate the thickness of the film is missing. The authors just show the film thickness equation without relating it to the pressure.
Response 1: Thank you very much for your valuable suggestions for this article. Your suggestions are very correct. Due to the limited level of the author, some details are not clearly stated, which has caused your misunderstanding in reading. I am deeply sorry for this. The author will explain this from the following aspects: The film thickness calculation in this paper considers the influence of pressure, the calculation of minimum film thickness in this paper is shown in formula
h = C(1+εcosθ) , the effect of pressure on the minimum film thickness is achieved by changing the eccentricity ε ( It has been supplemented with words “ε is eccentricity, it changes with the pressure in the fluid(as shown in Figure 3)” in red font in the article 4.1.1). As shown in Figure 3, at initial eccentricity ε0, calculate whether the force balance condition is met according to the internal pressure of the seal ring (the change of inlet pressure is taking into account), if not, the eccentricity shall be corrected, and the new minimum film thickness shall be calculated under the corrected eccentricity, then judge whether the force balance condition is met on the basis of the film thickness. If not, continue to correct the eccentricity. If yes, end the calculation, and so on. Here, thank you again for your criticism and correction!
Point 2: How do the authors ensure that the lubricant momentum is conserved? In the manuscript, the corresponding equations are missing.
Response 2: Thank you very much for your valuable comments. The questions you pointed out are very correct. Due to the limited level of the author, some details have not been taken into consideration and clearly expressed, which has caused your misunderstanding in reading. I am deeply sorry for this. Now the author has made a supplement to the momentum conservation equation in Section 4.1.3 of the revised version and marked it with red font. The formula is 16-a, 16-b and 16-c, and the reference document is [36]. Here, thank you again for your criticism and correction!
As there are many supplementary contents, they will be displayed with pictures, which is as follows:
Point 3: As stated in the paper, hydrodynamic lubrication will convert to a mixed lubrication regime when the lubricant fails to prevent contact. However, the equation for calculating the lubricants in such a regime is missing. Please elaborate in detail.
Response 3: Thank you very much for your valuable comments on this article. Your comments have been carefully considered. Due to the limited level of the author, some details have not been clearly stated, which has caused misunderstanding in your reading. I am deeply sorry for this. The calculation method of mixed lubrication state you pointed out is given in the paper, the calculation methods of gas film bearing capacity and friction power consumption under mixed lubrication are given in parts 4.1.4 and 4.2.2. The calculation formula will be shown in pictures as follows:
Figure 1. parts 4.1.4
Figure 2. parts 4.2.2
Point 4: As claimed by the authors, surface texturing is taken into account. However, I do not find the description of the texture, such as the shape, the dimensions, and the film thickness of the lubricant as a function of the surface texture profile.
Response 4: Thank you for your valuable comments on this article. Your correction is very accurate. Due to the author's negligence, the impact of surface roughness is mistakenly written as the impact of surface texture, which has caused your misunderstanding in reading. I am deeply sorry for this, it has been changed in red font at the abstract (replace "texturing" with " roughness ") and introduction (replace "texture" with " roughness "). The research content of this paper is mainly based on the average Reynolds equation, taking into account the influence of surface roughness and centrifugal expansion, and not taking into account the influence of surface texture. I'm sorry for your misreading, and thank you again for your valuable comments. Here, thank you again for your criticism and correction!
Author Response File: Author Response.docx
Round 2
Reviewer 3 Report
We appreciate your response. However, the author did not adequately address the roughness, which is an extremely important aspect. In the revised manuscript, the authors' methodology for modeling Roughness is absent. As stated in Eqs. 13-a and 13-b, the authors only present the average Reynolds equation in general form (i.e., without roughness). The comprehensive surface roughness (sigma) is not consistently defined. Please provide specific details.
Author Response
Point 1: We appreciate your response. However, the author did not adequately address the roughness, which is an extremely important aspect. In the revised manuscript, the authors' methodology for modeling Roughness is absent. As stated in Eqs. 13-a and 13-b, the authors only present the average Reynolds equation in general form (i.e., without roughness). The comprehensive surface roughness (sigma) is not consistently defined. Please provide specific details.
Response 1: Thank you very much for your suggestion. The problem you pointed out is very correct. Due to the author's negligence, the consideration of the problem is not careful enough, and some details are not clearly expressed, which has caused you difficulties in reading. I am very sorry for this. In the average Reynolds equation (13-b) used in the article, the influence of the comprehensive surface roughness on the lubrication performance of the sealing ring is realized through the influence Φx、Φy and Φs , and mark with yellow background color. The added content and calculation formula are shown in Figure 1:
Figure 1
Thank you again for your criticism and correction!
Author Response File: Author Response.docx
