A Novel Curve-and-Surface Fitting-Based Extrapolation Method for Sub-Idle Component Characteristics of Aeroengines

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The proposed method can be used to extend the characteristic maps of aeroengines into the sub-idle range. 

A great advantage of the presented method is the closed mathematical description by means of polynomials and fitting methods instead of using interpolation tables. Even if the method is not based on in-depth aerodynamic research, the more mathematically oriented curve fitting method is very well suited for practical applications. 

However, the quality of the extension depends heavily on the smoothness of the component maps (e.g. smoothness of maximum pressure ratio across the full speed range).  For relatively simple engines (components with few stages, without customer bleeds and cooling air requirements), the method works sufficiently well to safely control and monitor the engine start process as shown here.

 

There are only minor remarks:

Line 142: The phrase “inlet Mach number is 0” for ground bases tests can be misunderstood. A better phrase is recommended.

Line 146ff: Have all the velocity lines in Fig. 2 been predicted by tests or have smoothing, extrapolations etc. already been carried out? I recommend marking the design point and the design velocity line on the maps for better orientation.

Line 226ff. It should be emphasized that all leakages were also neglected.

Line 279: What is the reason for fixing the pressure ratio to 0.75.

Line 304: The unit for the corrected mass flow rate is wrong.

Chapter 3.2 I recommend adding the relative component speed in addition to the rpm value given.

Author Response

Please see the attachment，thank you.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper proposes an extrapolation method for sub-idle component characteristics of aeroengines based on curve and surface fitting. The method is applied to extrapolate the compressor and turbine characteristics of a micro turbojet engine and validate the results through ground-start simulations under different inlet conditions.

 

The modeling lacks certainty and needs to be experimentally checked. I can’t believe in negative efficiency values and values of pressure ratio less than one. This is against the law of turbomachinery. The companies may operate under windmilling with engine cutoff power and with free air stream conditions.

 

My great concern is why there are negative values; does this make physical sense?

 

 

QUERIES

1. Revise the title.
2. Check the English grammar and syntax errors thoroughly.
3. The Abstract should mention what problem was studied and what its importance is. What is the novelty of the work? What methods are used?
4. Provide a complete list of symbols and acronyms.
5. Revise the keywords list: some are inappropriate.
6. Citation within text must follow guidelines; please check with a published paper.
7. Elaborate more on how this physically happens: «compressors may operate in stirring or turbine modes, and turbines may function in stirring or compressor modes».
8. I do not agree with calling for the turbine to use «the pressure ratio.»
9. I do not agree to take the inlet Mach number =0.  
10. Why does Table 1 show the « Turbine outlet total temperature (K) », not « the inlet »
11. Give the equations used to plot Figures 1 and 2.
12. Iso-speeds are not shown in figures 1 and 2.
13. Many Figures are very blurry. Check fonts and curve colors.
14. In line 174, correct.
15. Why at sub-idle, the pressure ratio is below the value of one and efficiency less than zero.
16. Explain what different between stirring and turbine modes for the compressor.
17. Check stirring mode of the turbine: correctness of equations: 23-27
18. Explain what difference between stirring and compressor modes for the turbine.
19. Change the symbol of flow rate;  W means work.
20. Figure 2 or very confusing: what about really are they behaving like this mathematical model?
21. What model is used in Figure 3.
22. Equations should be supported by their references.
23. Conditions in line 304 are unclear. If rotational speed is 0 there is no flow rate.
24. In equation 44, what Z parameter mean
25. In line 312, what surface is used?
26. Line 313;  give reference.
27. What model is used in Figure 6.
28. Why is equation 65 modified, and why is there a value of 2 inside?
29. Are the characteristics in curves 9, 10 obtained experimentally? Explain.
30. What program was used to simulate results in Figures 11 and 12.
31. The conclusion is very general.

 

Comments on the Quality of English Language

see remarks

Author Response

Please see the attachment. Thank you!

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

I congratulate the authors on this significant improvement to the version of the articles, which addresses all of our concerns. 
The content and quality of the article appear sufficient for publication.