Experiments of Transpiration Cooling Inspired Panel Cooling on a Turbine Blade Yielding Film Effectiveness Levels over 95%^†

Round 1

Reviewer 1 Report

Mandatory Request Changes:Mandatory Changes: Requested changes which are essential for the understanding and completeness of the paper. Paper of author(s) who have not complied with these requests may be rejected.:
Page 9:
“While Panel 6 has a higher film effectiveness than Panel 1 at mean blowing ratios below 0.1 due to a better spanwise distribution, the maximum film effectiveness achieved does not exceed 0.65.” Attention: This description fits to panel 5 not panel 6!

Recommended Requested Changes:Recommended Changes: Changes will improve the quality of the paper. Authors are strongly encouraged to comply with these requests.:
Top1: Show the direction of the coolant supply e.g. add a sketch. This would ease the understanding of the spanwise non uniformity.

Top2: Show the hot gas side pressure distribution around the airfoil. This would give an idea about the variation of the gas side pressure from the leading to the trailing edge of the panels.

Top3: Give the representative gas side Re number, e.g based on chord length and blade roe exit conditions.

Additional Comment: Very nice investigation !

Author Response

1. Page 9:“While Panel 6 has a higher film effectiveness than Panel 1 at mean
blowing ratios below 0.1 due to a better spanwise distribution, the
maximum film effectiveness achieved does not exceed 0.65.”  Attention:
This description fits to panel 5 not panel 6!

Resolved

2. Top1: Show the direction of the coolant supply e.g. add a sketch.
This would ease the understanding of the spanwise non uniformity.

This has now been explicitly described in the text.

3. Top2: Show the hot gas side pressure distribution around the airfoil.
This would give an idea about the variation of the gas side pressure
from the leading to the trailing edge of the panels.

Due to the new requirements of our industry sponsor, this information can no longer be included in new publications. This information however is found in Reference Ngetich(2019) and has been referenced in the text.

4. Top3: Give the representative gas side Re number, e.g based on chord
length and blade roe exit conditions.
See (3)

Reviewer 2 Report

Mandatory Request Changes:Mandatory Changes: Requested changes which are essential for the understanding and completeness of the paper. Paper of author(s) who have not complied with these requests may be rejected.:
1. Nomenclature to be updated to include definitions for Blowing ratio and film effectiveness and all other parameters used in paper.
2. Table 1 to be updated to include hole length L, L/d, pitch/diameter, % cooling flows, etc and all parameters used in presentation of results. Terms should be non-dimensionalised for easier comparisons.
3. How is the film effectiveness spanwise averaged? A detailed explanation is needed in terms of non-dimensional streamwise and spanwise distances on the panel.
4. The external flow pressure distribution and acceleration parameter as a function of the entire blade axial perimeter is required to understand the film effectiveness results. Show positions of the cooling holes. Where is x/d = 0 in Fig 6.
5. Figure 11 and 12 are missing.
6. A plot similar to Fig 6, of film effectiveness with one nominal cooling flow and for all the panels is strongly recommended in order to see the relative merits of the different geometries.
7. A more detailed discussion of Fig 10 is required.
8. For journal publication, data on the Cd of the various panels should also be included to give a complete picture of the panel performances.

Recommended Requested Changes:Recommended Changes: Changes will improve the quality of the paper. Authors are strongly encouraged to comply with these requests.:
1. Nomenclature to be updated to include definitions for Blowing ratio and film effectiveness and all other parameters used in paper.
2. Table 1 to be updated to include hole length L, L/d, pitch/diameter, % cooling flows, etc and all parameters used in presentation of results. Terms should be non-dimensionalised for easier comparisons.
3. How is the film effectiveness spanwise averaged? A detailed explanation is needed in terms of non-dimensional streamwise and spanwise distances on the panel.
4. The external flow pressure distribution and acceleration parameter as a function of the entire blade axial perimeter is required to understand the film effectiveness results. Show positions of the cooling holes. Where is x/d = 0 in Fig 6.
5. Figure 11 and 12 are missing.
6. A plot similar to Fig 6, of film effectiveness with one nominal cooling flow and for all the panels is strongly recommended in order to see the relative merits of the different geometries.
7. A more detailed discussion of Fig 10 is required.
8. For journal publication, data on the Cd of the various panels should also be included to give a complete picture of the panel performances.

Author Response

1. Nomenclature to be updated to include definitions for Blowing
   ratio and film effectiveness and all other parameters used in paper

Resolved

2. Table 1 to be updated to include hole length L, L/d,
   pitch/diameter, % cooling flows, etc and all parameters used in
   presentation of results. Terms should be non-dimensionalised for easier
   

Table has been expanded to cover all relevant information of geometries

3. How is the film effectiveness spanwise averaged? A detailed
   explanation is needed in terms of non-dimensional streamwise and
   spanwise distances on the panel.

This information is now explicitly mentioned – the mean value of each row of pixels is calculated.

4. The external flow pressure distribution and acceleration parameter
   as a function of the entire blade axial perimeter is required to
   understand the film effectiveness results.

Due to the new requirements of our industry sponsor, this information can no longer be included in new publications. This information however is found in Reference Ngetich(2019) and has been referenced in the text.

5. Show positions of the cooling
   

This is shown in figure 1 and explicitly reference in the text.

6. Where is x/d = 0 in Fig 6.

This has now been explained in the text – x/d = 0 is the start of each panel.

7. Figure 11 and 12 are missing.

Figure numbering has been corrected.

8. A plot similar to Fig 6, of film effectiveness with one nominal
   cooling flow and for all the panels is strongly recommended in order to
   see the relative merits of the different geometries.

Figure 11 has been added to the text.

9. A more detailed discussion of Fig 10 is required.

The description of Fig 10 has been rewritten.

10. For journal publication, data on the Cd of the various panels
    should also be included to give a complete picture of the panel
    

Discharge coefficients and aerodynamic coefficients have been measured but the 10 page limit of this paper would not do all of the results justice so has been omitted for now. 

Reviewer 3 Report

Mandatory Request Changes:Mandatory Changes: Requested changes which are essential for the understanding and completeness of the paper. Paper of author(s) who have not complied with these requests may be rejected.:
Authors are kindly requested to comply with the following requests:
-provide information on the mainstream flow in terms of inlet Re, Mach and turbulence intensity, as well as outlet Ma.
-since PSP technique is not discussed, include the paper by Gurran et al. (2016b) in the list of references. At least, PSP measurement uncertainty is needed in this paper.
-include the blade loading and highlight the locations of panels 1-4. This would improve the discussion of the mainstream flow interaction with coolant (pags. 5-6).
- quantify the internal pressure, if possible.
- include specific references to figures 2-5 in the paper.
- quantify the minimum requirement (in terms of internal to external pressure difference) to obtain a film established over the entire span of the panel.
- figures 6 and 10 are not ready for black and white printing.
-include subheadings in the “results” section to separate the discussion on panels 1-4 from that starting at the beginning of pag.8.
- pag. 8 line 3: The effectiveness data of these panels is shown in Figures 7 and 8.
- bottom of pag. 8: add the reference to figure 9 in the manuscript.
- justify text in the whole manuscript.

Recommended Requested Changes:Recommended Changes: Changes will improve the quality of the paper. Authors are strongly encouraged to comply with these requests.:
-Did the authors measure the boundary layer thickness around the blade, especially where the panels are located?
-Did the authors measure the mainstream turbulence content at different axial planes, especially where the panels are located?

Author Response

1. provide information on the mainstream flow in terms of inlet Re, Mach
   and turbulence intensity, as well as outlet Ma.

Due to the new requirements of our industry sponsor, this information can no longer be included in new publications. This information is however found in Reference Ngetich(2019) and has been referenced in the text.

2. since PSP technique is not discussed, include the paper by Gurran et
   (2016b) in the list of references. At least, PSP measurement
   uncertainty is needed in this paper.

This issue has been resolved, now only a single Gurram paper is cited. This paper also includes a discussion about the associated errors in PSP measurements.

3. include the blade loading and highlight the locations of panels 1-4.
   This would improve the discussion of the mainstream flow interaction
   with coolant (pags. 5-6).

See (1)

4. quantify the internal pressure, if possible.

The total pressure ratio has been added to the results figures.

5. include specific references to figures 2-5 in the paper.

Resolved

6. quantify the minimum requirement (in terms of internal to external
   pressure difference) to obtain a film established over the entire span
   of the panel.

The total pressure ratio has been added to the results figures.

7. figures 6 and 10 are not ready for black and white printing.

These figures have been adjusted so that the legend includes symbols ontop of colours

8. include subheadings in the “results” section to separate the discussion
   on panels 1-4 from that starting at the beginning of pag.8.

Resolved

9. 8 line 3: The effectiveness data of these panels is shown in
   Figures 7 and 8.

Resolved

10. bottom of pag. 8: add the reference to figure 9 in the manuscript.

Resolved

11. justify text in the whole manuscript.

Resolved

12. Did the authors measure the boundary layer thickness around the
    blade, especially where the panels are located? Did the authors measure the mainstream turbulence content at different
    axial planes, especially where the panels are located?

Direct measurement of the boundary layer thickness  and turbulence around the blade has not yet been attempted.