Low-Pressure Turbine Cooling Systems

Round 1

Reviewer 1 Report

The article concerns analyzes related to the active control of the size of the gap between the tip of the rotor blade and the sealing of the turbine body. Active control of the amount of air supplied for cooling influences the size of the clearances and thus the efficiency of the turbine and its operational reliability. It is a very complex issue and any work related to it is valuable from a scientific and practical point of view. The work presented for review concerns only a literature review of these processes and, in my opinion, it should be reinforced with some own calculations that would allow to refer to this information. Only the equations describing the heat transfer are shown in the paper, but there is no information on the description of the impact of the gap size on the size of leakages, which directly affects the efficiency of the turbine stage and the entire turbine. It is discussed in the summary, and no literature analyzes have been conducted in this respect. The summary itself does not add any new and generally known information - so it would need to be redrafted. Of course, I am aware that the Encyclopedia journal has a slightly different character than the strictly scientific ones, nevertheless, in my opinion, the paper should be enriched.

Author Response

Dear reviewer,

Thank you for your comments and suggestions. Below please find explanations, comments and description of changes which were included in the article.

1. Additional text which refer to own calculations (influence of nozzle shape [24] and position [25] on heat transfer rate) to reinforce paper is included 
2. In introduction there is detailed information of influence of thermal tip clearance closure on turbine fuel consumption reduction. In this point of view data of reduced fuel consumption provided by Lattime and Steinetz [1] are treated as improvement of turbine efficiency. "Taking fuel savings into consideration, a reduction of tip clearance by 0.010-in. decreases specific fuel consumption by ~0.8 to 1 percent"  - (lines 34-35 of the text).
3. The summary of the paper is enriched with additional information. Physical and geometrical parameters which affects thermal tip clearance are presented. Impact of the surrounding environment on the heat transfer is included.

Reviewer 2 Report

Review of encyclopedia-1325278

Title: Turbine casings impingement cooling systems

Authors: Krzysztof Marzec

This paper presents a very fundamental review on the ACC system and its role on the engine. The quality of the paper cannot be considered enough for a Journal related to heat transfer, but with major revision it could published in encyclopedia. Most of the statements reported in the paper are generally included in the introductions of most of the papers regarding ACC system. Most of the references used for the review are published more than ten years ago with very short focus to the new papers (at ASME IGTI the ACC is still an important thematic and some EU calls were opened last years on this topic).

Below, I report the main point that must be discussed after a major revision:

1. The paper must include the most recent outcomes regarding ACC study. Please improve your review including recently published works.
2. Use recently published works to add a section regarding current state of investigation and a vision regarding possible improvements and open questions on this technology.
3. A section dedicated to numerical and experimental methods to study ACC should be provided.
4. As a general comment I do not see a clear identification regarding high pressure and low-pressure schemes for ACC system.
5. Section 4: I suggest to include basic correlations that can be used for the design (Nusselt, CD, cross flow effects ecc)

Specific comments:

1. Row 21 to 27: The positioning of this section is confusing: it is unclear that such advantages are obtained by reducing the tip clearance, and thus reducing the leakages and the associated losses. Please consider moving this section downstream, or adding some explanation regarding the reduction of tip losses directly upstream this section.
2. Ro 62 to 63: This sentence is unclear: maybe the author wants to state that that a different number of nozzles (i.e. a different amount of coolant) is employed in different regions along the engine axis according to the local casing temperature? If so, please rephrase this sentence.
3. Row 76 “Panel construction”: This definition is unclear: does the author means that the high pressure turbine ACC systems are manufactured with welded metal panels, i.e. using square/rectangular section ducts? Please clarify.
4. Missing reference for Fig.4, 6
5. Check typos, for example: lengths, quire, an starting point, ration, commas not properly used etc.
6. Section 5: Most of the phenomena presented in this section are derived from studies which deal with single impinging jets or 2D arrays of jets, which are weakly representative of ACC systems.The reviewer suggests to enrich the literature review with more papers specifically focused on ACC devices. in terms of both heat transfer and flow features. In particular, please consider the followings:
   10. - R. Goldstein and W. Seol, ‘Heat transfer to a row of impinging circular air jets including the effect of entrainment.’, Int J Heat Mass Transf., vol. 34, pp. 2133–47, 1991, doi: 10.1016/0017-9310(91)90223-2.
   11. - F. Ben Ahmed, R. Tucholke, B. Weigand, and K. Meier, ‘Numerical Investigation of Heat Transfer and Pressure Drop Characteristics for Different Hole Geometries of a Turbine Casing Impingement Cooling System’, May 2012, pp.  095–1108, doi: 10.1115/GT2011-45251
   12. - F. Liu, J. Mao, C. Han, Y. Liu, X. Han, and F. Liang, ‘Study of a Cooling Feed Pipe With a Covering Plate on a Ribbed Turbine Case’, J. Eng. Gas Turbines Power, vol. 141, no. 7, Jul. 2019, doi: 10.1115/1.4043445
   13. - R. Da Soghe and C. Bianchini, ‘Aero-Thermal Investigation of Convective and Radiative Heat Transfer on Active Clearance Control Manifolds’, presented at the ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition, Nov. 2019, doi: 10.1115/GT2019-90007
   14. - R. Da Soghe, C. Bianchini, A. Andreini, B. Facchini, and L. Mazzei, ‘Heat Transfer Augmentation due to Coolant Extraction on the Cold Side of Active Clearance Control Manifolds’, J. Eng. Gas Turbines Power, vol. 138, no. 2, Feb. 2016, doi: 10.1115/1.4031383
   15. - Da Soghe, R., Mazzei, L., Tarchi, L., Cocchi, L., Picchi, A., Facchini, B., ... & Simon, M. (2021). Development of Experimental and Numerical Methods for the Analysis of Active Clearance Control Systems. Journal of Engineering for Gas Turbines and Power, 143(2), 021018.
7. Where is ref 35??
8. Row 254 to 256: This sentence looks like a repetition of what is stated above and would better fit in the "conclusions" section.

Author Response

Dear Reviewer,

Thank you for your comments, remarks and suggestions.

Below please find my comments and answers:

I. Main points:

1. Most recent studies regarding ACC are included in the paper.

2.  Section regarding current state of investigation and a vision regarding possible improvements on this technology is added.

3. Chapter dedicated to the numerical and experimental methods of ACC study is included.

4. Agree that there is no clear identification between LP and HP turbine cooling systems in the presented paper. Paper is focused mostly on LP turbine cooling systems (design description, schematic section and tip clearance control diagram). Since design, thermal requirements and flow characteristic of HP turbine are different then LP turbine minor section with HP turbine description is removed.  Title of the paper is limited in accordance.  

5. Chapter 4 is enriched with additional correlations describing heat transfer and flow behavior (line average Nusselt number, area averaged Nusselt number, Reynolds number, coefficient factor). Additionally description of the cross-flow effect and interaction of spent flow with fresh nozzle flow is included. 

II. Specific comments:

1. Explanation regarding the reduction of tip losses in terms of the ACC installation is added above the line 21.
2. Sentence (lines 62-63) is rephrased to make understanding more clear.  
3. Sentence (line 76) was removed since it was addressed to the HP turbines. - see point 4 from main points.
4. References to the fig. 4 is added. Fig. 6 is author own schematic draft.  
5. Typing errors are corrected.
6.  Paper is enriched with information provided from papers focused on ACC devices. 
7. Ref. "35" is typing error. It's corrected to ref. "12".
8. Line 254-256 is moved to the "conclusions" chapter.

Round 2

Reviewer 1 Report

The authors took into account the comments of the reviewer to a satisfactory degree for the publication of the article in the journal Encyclopedia. 

Reviewer 2 Report

I appreciate the effort of the Author. Now the paper can be considered acceptable looking to the final intent of the Journal.