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Research Papers: Gas Turbines: Structures and Dynamics

Model of Effect of Hot Gas Ingress on Temperatures of Turbine Disks

[+] Author and Article Information
J. Michael Owen

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: J.M.Owen@bath.ac.uk

Hui Tang

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: H.Tang2@bath.ac.uk

Gary D. Lock

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: G.D.Lock@bath.ac.uk

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received May 23, 2018; final manuscript received June 18, 2018; published online August 31, 2018. Editor: David Wisler.

J. Eng. Gas Turbines Power 141(1), 012501 (Aug 31, 2018) (9 pages) Paper No: GTP-18-1225; doi: 10.1115/1.4040680 History: Received May 23, 2018; Revised June 18, 2018

Ingress is the leakage of hot mainstream gas through the rim-seal clearance into the wheel-space between the rotating turbine disk (the rotor) and the adjacent stationary casing (the stator). The high-pressure rotor is purged by a radial outflow of air from the high-pressure compressor, and this cooling air is also used to reduce the ingress. The engine designer needs to predict the stator and rotor temperatures as a function of cooling-flow rate. The sealing effectiveness determines how much air is needed to reduce or prevent ingress; although there are numerous theoretical and experimental papers on the effectiveness of different seal geometries, there are few papers on the effect of ingress on the temperature of the rotating disk. This is an unsolved problem of great practical importance: under high stress, a small increase in metal temperature can significantly reduce operating life. In this paper, conservation equations and control volumes are used to develop theoretical equations for the exchange of mass, concentration and enthalpy in an adiabatic rotor–stator system when ingress occurs. It is assumed that there are boundary layers on the rotor and stator, separated by an inviscid rotating core, and the fluid entrained from the core into the boundary layer on the rotor is recirculated into that on the stator. The superposed cooling flow protects the rotor surface from the adverse effects of hot-gas ingress, which increases the temperature of the fluid entrained into the rotor boundary layer. A theoretical model has been developed to predict the relationship between the sealing effectiveness on the stator and the adiabatic effectiveness on the rotor, including the effects of both ingress and frictional heating. The model involves the use of a nondimensional buffer parameter, Ψ, which is related to the relative amount of fluid entrained into the rotor boundary layer. The analysis shows that the cooling flow acts as a buffer, which attenuates the effect of hot gas ingress on the rotor, but frictional heating reduces the buffer effect. The theoretical effectiveness curves are in good agreement with experimental data obtained from a rotor–stator heat-transfer rig, and the results confirm that the buffer effect increases as the sealing effectiveness of the rim seals decreases. The analysis quantifies the increase in the adiabatic rotor temperature due to direct frictional heating, which is separate from the increase due to the combined effects of the ingress and the indirect frictional heating of the entrained fluid. These combined effects are reduced as Ψ increases, and Ψ = 1 at a critical flow rate above which there is no entrained fluid and consequently no indirect heating of the rotor. The model also challenges the conventional physical interpretation of ingress as, in general, not all the hot gas that enters the rim-seal clearance can penetrate into the wheel-space. The ingress manifests itself through a mixing of enthalpy, which can be exchanged even if no ingested fluid enters the wheel-space.

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References

Scobie, J. A. , Sangan, C. M. , Owen, J. M. , and Lock, G. D. , 2016, “ Review of Ingress in Gas Turbines,” ASME J. Eng. Gas Turbines Power, 138(12), p. 120801. [CrossRef]
Chew, J. W. , Green, T. , and Turner, A. B. , 1994, “ Rim Sealing of Rotor-Stator Wheelspaces in the Presence of External Flow,” ASME Paper No. 94-GT-126.
Pountney, O. J. , Sangan, C. M. , Lock, G. D. , and Owen, J. M. , 2013, “ Effect of Ingestion on Temperature of Turbine Disks,” ASME J. Turbomach., 135(5), p. 051010. [CrossRef]
Cho, G. , Sangan, C. M. , Owen, J. M. , and Lock, G. D. , 2016, “ Effect of Ingress on Turbine Disks,” ASME J. Eng. Gas Turbines Power, 138(4), p. 042502. [CrossRef]
Mear, L. I. , Owen, J. M. , and Lock, G. D. , 2016, “ Theoretical Model to Determine Effect of Ingress on Turbine Disks,” ASME J. Eng. Gas Turbines Power, 138(3), p. 032502. [CrossRef]
Tian, S. , Zhang, Y. , and Su, W. , 2014, “ Effects of Gas-Ingestion Through Turbine Rim Seals on Flow and Heat Transfer in the Wheel-Space,” ASME Paper No. GT2014-26635.
Childs, P. R. N. , 2011, Rotating Flow, Elsevier, Oxford, UK.
Sangan, C. M. , Lalwani, Y. , Owen, J. M. , and Lock, G. D. , 2013, “ Experimental Measurements of Ingestion Through Turbine Rim Seals: Part 5—Fluid Dynamics of Wheel-Space,” ASME Paper No. GT2013-94148.
Mear-Stone, L. , 2015, “ Theoretical Modelling of Flow in Rotor-Stator Systems,” Ph.D. thesis, University of Bath, Bath, UK. http://opus.bath.ac.uk/49317/1/Complete_Thesis_Final_Post_Viva_Corrected_Aligned.pdf
Owen, J. M. , 2011, “ Prediction of Ingestion Through Turbine Rim Seals—Part I: Rotationally Induced Ingress,” ASME J. Turbomach., 133(3), p. 031005. [CrossRef]
Owen, J. M. , 2011, “ Prediction of Ingestion Through Turbine Rim Seals—Part II: Externally Induced and Combined Ingress,” ASME J. Turbomach., 133(3), p. 031006. [CrossRef]
White, F. M. , 2011, Fluid Mechanics, McGraw-Hill, New York.
Owen, J. M. , and Rogers, R. H. , 1989, Flow and Heat Transfer in Rotating-Disc Systems, Volume 1: Rotor-Stator Systems, Research Studies Press, Taunton, UK.
Sangan, C. M. , Pountney, O. J. , Zhou, K. , Wilson, M. , Owen, J. M. , and Lock, G. D. , 2011, “ Experimental Measurements of Ingestion Through Turbine Rim Seals—Part II: Rotationally Induced Ingress,” ASME J. Turbomach., 135(2), p. 021013. [CrossRef]

Figures

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Fig. 2

Simplified model of flow structure in wheel-space

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Fig. 1

Generic rotor–stator turbine stage, showing rim seal [1]

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Fig. 3

Control volumes for concentration: (a) outer control volume and (b) inner control volume

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Fig. 4

Control volumes for enthalpy: (a) outer control volume and (b) inner control volume

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Fig. 7

Variation of εc,sandεH′,r with Φ0. (Symbols denote experimental data [4]; curves show theoretical correlations): (a) axial-clearance seal and (b) radial-clearance seal.

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Fig. 5

Test section showing instrumentation in wheel-space [4]

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Fig. 6

Rim-seal configurations [4]

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Fig. 8

Variation of Ψ with Φ0. (Symbols denote experimental data [5]; curve shows theoretical correlation.)

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