Conjugate Heat Transfer Characteristics in a Highly Thermally Loaded Film Cooling Configuration with TBC in Syngas
Round 1
Reviewer 1 Report
This paper presents conjugate heat transfer characteristics (namely, metal temperature) in a film cooling arrangement on a flat plate both experimentally and numerically. The effects of radiation heat transfer, composition of gas from combustion chamber and thermal barrier coating (TBC) are investigated. Through the use of commercial numerical solver, which is validated by experimental data on the same configuration, this paper concludes that radiation and high percentage of steam in gas composition increase temperature on the film-cooled plate, and the temperature drop across TBC is larger if the radiation effect is more significant.
The methodology in this paper is rigorous and thus the results are reasonably convincing. The conclusions made should be useful for gas turbine designer since radiation, gas composition and TBC are relevant in engine product but their effects on metal temperature are less well-known. Acceptance of this paper is subject to the authors addressing the following questions:
1. Contribution of this paper needs to be delineated more clearly in the introduction section, after reviewing the state of the art research. What is this paper’s originality and uniqueness compared to existing literature?
2. What is the rationale for choosing different hot gas compositions in Table 2? Why a water supply system was installed downstream of the burner to adjust the steam composition, instead of using the burned gas directly which is more representative of gas turbine combustor exhaust?
3. It is stated in the abstract that “(when considering radiation) temperature gradient of the film cooled plate becomes larger”, but the last sentence in Section 4.1 says that “radiation weakens the temperature gradient”. Please double check this contradiction.
4. In Figure 10, the effect of radiation on the temperature of top and bottom plates is opposite, i.e. temperature of top plate increases while that of bottom plate decreases with radiation, why is it?
5. In the results and discussion section, it is better to compare the result/conclusion of this paper to that reported in literature whenever possible. Alignment with existing studies would boost the credibility of the present results.
6. Please proof-read this paper again and correct grammatical errors and typos, such as “date” in Line 44, “gas has” in Line 267, “is grows” in Line 293, etc.
Author Response
Reviewer 1
The authors appreciate the review and suggestions of the reviewer, and we have revised the paper according to your advice.
1. Contribution of this paper needs to be delineated more clearly in the introduction section, after reviewing the state of the art research. What is this paper’s originality and uniqueness compared to existing literature?
A: the contribution of this paper is to review previous studies about radiation, multicomposition and TBC. The following sentence has been added in the introduction to clear the objective of the paper: “In the present study, previous researches in our group are reviewed to show the effects of radiation heat transfer, multi-composition gas and TBC on high temperature film-cooled plate from experimental and numerical aspects”.
2. What is the rationale for choosing different hot gas compositions in Table 2? Why a water supply system was installed downstream of the burner to adjust the steam composition, instead of using the burned gas directly which is more representative of gas turbine combustor exhaust?
A: The water supply system is used to vary the steam humidity of hot gas and change the gas composition. This is used to investigate the effect of multi-composition on the conjugate heat transfer performance of film-cooled plate.
3. It is stated in the abstract that “(when considering radiation) temperature gradient of the film cooled plate becomes larger”, but the last sentence in Section 4.1 says that “radiation weakens the temperature gradient”. Please double check this contradiction.
A: it has been revised to:” temperature gradient of the film cooled plate becomes less significant”
4. In Figure 10, the effect of radiation on the temperature of top and bottom plates is opposite, i.e. temperature of top plate increases while that of bottom plate decreases with radiation, why is it?
A: the effect is not opposite. For no radiation case, the Y axis is left side; for radiation case, the Y axis is right side. So for both top and bottom plates, radiation increases the temperature level.
5. In the results and discussion section, it is better to compare the result/conclusion of this paper to that reported in literature whenever possible. Alignment with existing studies would boost the credibility of the present results.
A: the authors want to compare the data with previous literature. But there are scare studies on the high temperature effects on film-cooled plate. And also the boundary conditions differ a lot for different studies, which hamper the comparison between different studies.
6. Please proof-read this paper again and correct grammatical errors and typos, such as “date” in Line 44, “gas has” in Line 267, “is grows” in Line 293, etc.
A: the paper has been carefully revised and the grammatical errors have been corrected.
Reviewer 2 Report
1. Fig. 2
Where is the diluting section? Please indicate on Fig.2.
2. Fig. 3 (b)
Only five holes are shown in Fig.3 (b). Holes are seven, aren’t they? Please correct the figure.
3. Fig. 3 (b)
Please move the coordinate system indicator to the origin.
4. Line 115 “The thermal conductivities of the superalloy plate and TBC are 20W/mK and 2W/mK,”
What is the temperature that the materials show those thermal conductivities?
5. Line 130
Regarding Fig.5, thermo-couples on the center line are 30 [10×3 plane(top, middle, bottom)]. Please check and correct if it is needed.
6. Fig.5
It is not needed to show measurement line routings. Showing only measurement points is enough for information to be included in Fig.5.
7. Line 170
The first word “indicated” is expressed in different font.
8. Fig. 6
Please add boundary condition information.
9. Table 2
Do these three cases simulate components of gases got by burning some kind of actual fuels? If the answer is yes, please add the information of kind of fuels.
10. Table 3
Please add blowing ratio of film cooling air to main flow.
11. Fig. 8
Please use different colors in plotting experimental data of top and bottom.
12. Fig. 8
Please plot experimental data all of the 10 measurement points on the centerline.
13. Fig. 8
Please compare numerical result with experimental data on the on the line E (shown in Fig.5).
14. Line 222
Please show the test condition using for the numerical validation in this paper.
15. Fig.10
The data in Fig.10 is not spanwise averaged data. Please correct the title of the figure.
16. Line 229 “Continually, the spanwise averaged temperature profiles…..”
The data in Fig.10 is not spanwise averaged data. So this sentence should be corrected to the sentence of “Continually, the spanwise averaged temperature profiles at X/D=1.0…..”.
17. Line 246 “…..effect is weakened by radiation…”
This reviewer thinks that it is not because of radiation, but because of conductivity of the wall material. The reason that this reviewer thinks so is that the blue line in Fig.11 that is no-radiation case also shows small gradient.
18. Line 249 “The radiation enhances the temperature increasing, but weakens the temperature gradient.”
This reviewer thinks that it is not because of radiation, but because of conductivity of the wall material. The reason that this reviewer thinks so is that the blue line in Fig.11 that is no-radiation case also shows small gradient.
19. Fig.11
Experimental data points on the centerline (line D in Fig.5) are 10, aren’t they? Plotted data are only 4 in Fig.11 Please plot all data obtained.
20. Table 4
Please add mainflow condition (temperature, mass flow rate, outlet pressure) and blowing ratio of film cooling air to mainflow.
21. Table 4
Please add a gas composition of conventional jet fuel for comparison.
22. 261-262 “Without considering radiative heat transfer, the temperature distributions are similar for five different fuel cases.”
The result of Oxy is different from other four cases. Please correct the sentence.
23. Fig. 12
NG resembles LPG in the composite of burning gas. But radiation heating effects on the surface temperature are different. Please explain your understanding for this result.
24. Table 5
Please add mainflow condition (temperature, mass flow rate, outlet pressure) and blowing ratio of film cooling air to mainflow.
25. Fig.13
Please plot experimental data of D-F2 point (on centerline at 25D). And it is better if you use the same scale for three graphs.
26. Fig.13 and Fig.8
Plots on those two figures show different temperature trend with x from the temperature trend with x of the plots on Fig. 11 and Fig.12. The temperature in Fig.11 and Fig.12 decrease monotonically with x. What is the reason of the difference?
27. Fig.14
Please plot experimental data of D-F2 point (on centerline at 25D). And it is better if you use the same scale for three graphs.
28. Fig.14
There are non-continuous changes between measurement point 1 and 3, and between 5 and F1. Why are those non-continuous changes caused? Please describe your understandings.
29. Line 289-290 “which indicates the temperature drop by TBC is higher when radiation effect is stronger”
Is this understanding correct? Increase of H2O causes increase in heat transfer coefficient, and increase in heat transfer coefficient causes increase in heat flux. This may be the reason.
30. Line 294-295 “This is caused by the radiation property differences between TBC and nickel-based alloy.”
This may be one of the reasons. But the difference in heat transfer coefficients between gas composites may be the reason, too.
31. Line 295 “when TBC is coated, over 50% of the radiation heat transfer is reflected by TBC.”
Please describe emissivity of TBC surface.
32. Line 297-298 “Another advantage of TBC is that it smooths the temperature distribution and decreases the temperature gradient to some extent.”
This reviewer thinks that it is not because of radiation, but because of conductivity of the wall material.
33. Line 298 “More discussion can be found in [33].”
Please describe necessary discussions in this paper.
34. Conclusion
Please consider this reviewer’s comments, and please correct conclusion if it is needed.
end
Author Response
Reviewer 2
The authors appreciate the review and suggestions of the reviewer, and we have revised the paper according to your advice.
1. Fig. 2
Where is the diluting section? Please indicate on Fig.2.
A: the water supply section is the diluting section.
2. Fig. 3 (b)
Only five holes are shown in Fig.3 (b). Holes are seven, aren’t they? Please correct the figure.
A: it has been corrected.
3. Fig. 3 (b)
Please move the coordinate system indicator to the origin.
A: it has been corrected.
4. Line 115 “The thermal conductivities of the superalloy plate and TBC are 20W/mK and 2W/mK,”
What is the temperature that the materials show those thermal conductivities?
A:it is measured at 550C.
5. Line 130
Regarding Fig.5, thermo-couples on the center line are 30 [10×3 plane(top, middle, bottom)]. Please check and correct if it is needed.
A: it has been checked and it is need.
6. Fig.5
It is not needed to show measurement line routings. Showing only measurement points is enough for information to be included in Fig.5.
A: the authors think it will be clearer to show the line routings.
7. Line 170
The first word “indicated” is expressed in different font.
A: it has been revised.
8. Fig. 6
Please add boundary condition information.
A: the boundary condition is in the section 3.4.
9. Table 2
Do these three cases simulate components of gases got by burning some kind of actual fuels? If the answer is yes, please add the information of kind of fuels.
A: more information can be referred in [28].
10. Table 3
Please add blowing ratio of film cooling air to main flow.
A: The blowing ratio is calculated to be 1.0.
11. Fig. 8
Please use different colors in plotting experimental data of top and bottom.
A:
12. Fig. 8
Please plot experimental data all of the 10 measurement points on the centerline.
A:
13. Fig. 8
Please compare numerical result with experimental data on the on the line E (shown in Fig.5).
A:
14. Line 222
Please show the test condition using for the numerical validation in this paper.
A: the numerical conditions are similar to experimental conditions as shown in table 2.
15. Fig.10
The data in Fig.10 is not spanwise averaged data. Please correct the title of the figure.
A: it has been revised.
16. Line 229 “Continually, the spanwise averaged temperature profiles…..”
The data in Fig.10 is not spanwise averaged data. So this sentence should be corrected to the sentence of “Continually, the spanwise averaged temperature profiles at X/D=1.0…..”.
A: it has been revised.
17. Line 246 “…..effect is weakened by radiation…”
This reviewer thinks that it is not because of radiation, but because of conductivity of the wall material. The reason that this reviewer thinks so is that the blue line in Fig.11 that is no-radiation case also shows small gradient.
A: the authors think the radiation will heat the whole surface and increases the whole surface temperature. This decreases the temperature gradient. Maybe the variation of conductivity of the wall material plays a role in the phenomenon.
18. Line 249 “The radiation enhances the temperature increasing, but weakens the temperature gradient.”
This reviewer thinks that it is not because of radiation, but because of conductivity of the wall material. The reason that this reviewer thinks so is that the blue line in Fig.11 that is no-radiation case also shows small gradient.
A: the authors think the radiation will heat the whole surface and increases the whole surface temperature. This decreases the temperature gradient. Maybe the variation of conductivity of the wall material plays a role in the phenomenon.
19. Fig.11
Experimental data points on the centerline (line D in Fig.5) are 10, aren’t they? Plotted data are only 4 in Fig.11 Please plot all data obtained.
A:
20. Table 4
Please add mainflow condition (temperature, mass flow rate, outlet pressure) and blowing ratio of film cooling air to mainflow.
A: the flow boundary conditions are similar to table 3.
21. Table 4
Please add a gas composition of conventional jet fuel for comparison.
A:
22. 261-262 “Without considering radiative heat transfer, the temperature distributions are similar for five different fuel cases.”
The result of Oxy is different from other four cases. Please correct the sentence.
A: it has been revised.
23. Fig. 12
NG resembles LPG in the composite of burning gas. But radiation heating effects on the surface temperature are different. Please explain your understanding for this result.
A:
24. Table 5
Please add mainflow condition (temperature, mass flow rate, outlet pressure) and blowing ratio of film cooling air to mainflow.
A: the flow boundary conditions are similar to table 3.
25. Fig.13
Please plot experimental data of D-F2 point (on centerline at 25D). And it is better if you use the same scale for three graphs.
A:
26. Fig.13 and Fig.8
Plots on those two figures show different temperature trend with x from the temperature trend with x of the plots on Fig. 11 and Fig.12. The temperature in Fig.11 and Fig.12 decrease monotonically with x. What is the reason of the difference?
A:
27. Fig.14
Please plot experimental data of D-F2 point (on centerline at 25D). And it is better if you use the same scale for three graphs.
A:
28. Fig.14
There are non-continuous changes between measurement point 1 and 3, and between 5 and F1. Why are those non-continuous changes caused? Please describe your understandings.
A:
29. Line 289-290 “which indicates the temperature drop by TBC is higher when radiation effect is stronger”
Is this understanding correct? Increase of H2O causes increase in heat transfer coefficient, and increase in heat transfer coefficient causes increase in heat flux. This may be the reason.
A: Yes, it is.
30. Line 294-295 “This is caused by the radiation property differences between TBC and nickel-based alloy.”
This may be one of the reasons. But the difference in heat transfer coefficients between gas composites may be the reason, too.
A: the reason the reviewer proposed makes sense.
31. Line 295 “when TBC is coated, over 50% of the radiation heat transfer is reflected by TBC.”
Please describe emissivity of TBC surface.
A:
32. Line 297-298 “Another advantage of TBC is that it smooths the temperature distribution and decreases the temperature gradient to some extent.”
This reviewer thinks that it is not because of radiation, but because of conductivity of the wall material.
A: the conductivity of the wall material maybe another reason.
33. Line 298 “More discussion can be found in [33].”
Please describe necessary discussions in this paper.
A:
34. Conclusion
Please consider this reviewer’s comments, and please correct conclusion if it is needed.
A:
Round 2
Reviewer 1 Report
The authors address my concern appropriately. The quality of writing and readibility of the paper is improved now to a reasonable standard of the journal.
Author Response
Thank you for your reply.
Reviewer 2 Report
Thank you for correcting the paper. But following comments are still waiting your answers or correction.
4. Line 115 “The thermal conductivities of the superalloy plate and TBC are 20W/mK and 2W/mK,”
What is the temperature that the materials show those thermal conductivities?
Please describe the temperature(550℃) in the text.
5. Line 130
Regarding Fig.5, thermo-couples on the center line are 30 [10×3 plane(top, middle, bottom)]. Please check and correct if it is needed.
This reviewer understands that “downstream area of the centered film cooling hole” indicates the line D in Fig.5. Is my understanding right? Or do authors use “downstream area of the centered film cooling hole” to indicate downstream area including from line A to E?
If “downstream area of the centered film cooling hole” indicates the line D, thermocouples on line D is 30, I think.
8. Fig. 6
Please show boundary condition visually in Fig.6.
9. Table 2
Do these three cases simulate components of gases got by burning some kind of actual fuels? If the answer is yes, please add the information of kind of fuels.
Thank you for adding reference number. I hope authors describe brief explanation for those cases in this paper.
12. Fig. 8
Please plot experimental data all of the 10 measurement points on the centerline.
Centerline means line D in Fig.5. This reviewer believes that 10 thermocouples exist on line D on each surface. Plot points are less than 10. So this reviewer thinks that there is lack of experimental data plots in this figure.
13. Fig. 8
Please compare numerical result with experimental data on the on the line E (shown in Fig.5).
This reviewer requests to add similar figure as Fig.8 regarding line E (in Fig.5).
14. Line 222
Please show the test condition using for the numerical validation in this paper.
Thank you for your answer. But Table 2 doesn’t include information of mass fraction. So readers cannot distinguish the test case used in the numerical study from 3 cases in Table 2.
17. Line 246 “…..effect is weakened by radiation…”
This reviewer thinks that it is not because of radiation, but because of conductivity of the wall material. The reason that this reviewer thinks so is that the blue line in Fig.11 that is no-radiation case also shows small gradient.
Thank you for your answer. I agree with that the radiation heat the whole surface up and increases the whole surface temperature. But I don’t agree with your conclusion that radiation decreases the temperature gradient. The blue line (“no-radiation-num”) in Fig.11 shows similar non-dimensional temperature gradient with the red line (“with-radiation-num”). This is the evidence that the reason of the different temperature gradient is not radiation. On the other hand, I believe that we can know thermal conductivity effect by comparing blue line (“no-radiation-num”) and pink line(“no-radiation-num-ad”) in Fig.11. The non-dimensional temperature gradient of blue line is different from that of the pink line. This is evidence of the reason that I think the different temperature gradient is because of the thermal conductivity of the material.
18. Line 249 “The radiation enhances the temperature increasing, but weakens the temperature gradient.”
This reviewer thinks that it is not because of radiation, but because of conductivity of the wall material. The reason that this reviewer thinks so is that the blue line in Fig.11 that is no-radiation case also shows small gradient.
Same as an additional comment for 17.
19. Fig.11
Experimental data points on the centerline (line D in Fig.5) are 10, aren’t they? Plotted data are only 4 in Fig.11 Please plot all data obtained.
20. Table 4
Please add mainflow condition (temperature, mass flow rate, outlet pressure) and blowing ratio of film cooling air to mainflow.
Please describe that the test condition is similar to table 3.
21. Table 4
Please add a gas composition of conventional jet fuel for comparison.
22. 261-262 “Without considering radiative heat transfer, the temperature distributions are similar for five different fuel cases.”
The result of Oxy is different from other four cases. Please correct the sentence.
Following sentence is described in the text in Ver.2. “Without considering radiative heat transfer, the temperature distributions are similar for six different fuel cases.”
There are only 5 types of fuels.
23. Fig. 12
NG resembles LPG in the composite of burning gas. But radiation heating effects on the surface temperature are different. Please explain your understanding for this result.
24. Table 5
Please add mainflow condition (temperature, mass flow rate, outlet pressure) and blowing ratio of film cooling air to mainflow.
Please describe that the test condition is similar to table 3.
25. Fig.13
Please plot experimental data of D-F2 point (on centerline at 25D). And it is better if you use the same scale for three graphs.
26. Fig.13 and Fig.8
Plots on those two figures show different temperature trend with x from the temperature trend with x of the plots on Fig.12. The temperature in Fig.12 increases monotonically with x. What is the reason of the difference? Please describe your understanding in the text.
27. Fig.14
Please plot experimental data of D-F2 point (on centerline at 25D). And it is better if you use the same scale for three graphs.
28. Fig.14
There are non-continuous changes between measurement point 1 and 3, and between 5 and F1. Why are those non-continuous changes caused? Please describe your understandings.
29. Line 289-290 “which indicates the temperature drop by TBC is higher when radiation effect is stronger”
Is this understanding correct? Increase of H2O causes increase in heat transfer coefficient, and increase in heat transfer coefficient causes increase in heat flux. This may be the reason.
Don’t you think this reviewer’s comment is another possible understanding? If you think so, this reviewer suggests that you add possible explanations in the text if you agree with my comment.
30. Line 294-295 “This is caused by the radiation property differences between TBC and nickel-based alloy.”
This may be one of the reasons. But the difference in heat transfer coefficients between gas composites may be the reason, too.
This reviewer suggests that you add possible explanations in the text if you agree with my comment.
31. Line 295 “when TBC is coated, over 50% of the radiation heat transfer is reflected by TBC.”
Please describe emissivity of TBC surface.
32. Line 297-298 “Another advantage of TBC is that it smooths the temperature distribution and decreases the temperature gradient to some extent.”
This reviewer thinks that it is not because of radiation, but because of conductivity of the wall material.
This reviewer suggests that you add possible explanations in the text if you agree with my comment.
33. Line 298 “More discussion can be found in [33].”
Please describe necessary discussions in this paper.
34. Conclusion
Please consider this reviewer’s comments, and please correct conclusion if it is needed.
end
Author Response
4. Please describe the temperature (550℃) in the text.
A: It has been added in the text.
8. Please show boundary condition visually in Fig.6.
A: the boundary conditions have been added in the figure.
12. Centerline means line D in Fig.5. This reviewer believes that 10 thermocouples exist on line D on each surface. Plot points are less than 10. So this reviewer thinks that there is lack of experimental data plots in this figure.
13. This reviewer requests to add similar figure as Fig.8 regarding line E (in Fig.5).
A: the thermocouples on the line E are destroyed due to the high temperature mainstream, so we cannot obtain experimental data on the line E.
14. Thank you for your answer. But Table 2 doesn’t include information of mass fraction. So readers cannot distinguish the test case used in the numerical study from 3 cases in Table 2.
A: the table 2 provided the volume fraction and therefore the mass fraction can be calculated.
19. Please plot all data obtained.
A: the other 6 thermocouples are destroyed, so we cannot obtain any data in the experiments.
20. Please describe that the test condition is similar to table 3.
A: table 3 shows the test condition.
21. Please add a gas composition of conventional jet fuel for comparison.
A: the present study is targeted at the fuel of heavy-duty gas turbine, so the authors doesn’t have data for gas composition of conventional jet fuel.
22. Following sentence is described in the text in Ver.2. “Without considering radiative heat transfer, the temperature distributions are similar for six different fuel cases.” There are only 5 types of fuels.
A: it is revised.
23. Please explain your understanding for this result.
A: there still exists some difference between NG and LPG. The authors think that it is the difference causes the different radiation behaviours.
24. Please describe that the test condition is similar to table 3.
A: table 3 shows the test condition.
Author Response File: 
Author Response.docx
Round 3
Reviewer 2 Report
Review Comments to aerospace-396659-V3
aerospace-396659
Conjugate heat transfer characteristics in a highly thermally loaded film cooling configuration with TBC in syngas
Thank you for correcting the paper. But following comments are still waiting your answers or correction.
28. Fig.14
There are non-continuous changes between measurement point 1 and 3, and between 5 and F1.
Why are those non-continuous changes caused? Please describe your understandings.
31. Line 295 “when TBC is coated, over 50% of the radiation heat transfer is reflected by TBC.”
Please describe emissivity of TBC surface.
33. Line 298 “More discussion can be found in [33].”
Please describe necessary discussions in this paper.
end
Author Response
28. Fig.14
There are non-continuous changes between measurement point 1 and 3, and between 5 and F1. Why are those non-continuous changes caused? Please describe your understandings.
A: the results are suspected to be caused the interaction between film cooling and radiation heat transfer.
31. Line 295 “when TBC is coated, over 50% of the radiation heat transfer is reflected by TBC.”
Please describe emissivity of TBC surface.
A: it is 0.1.
33. Line 298 “More discussion can be found in [33].”
Please describe necessary discussions in this paper.
A: The necessary discussions already included in this paper. The sentenced has been deleted.
