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Research Papers

Effects of Coolant Density, Specific Heat Capacity, and Biot Number on Turbine Vane Cooling Effectiveness

[+] Author and Article Information
S. Luque

Department of Engineering Science,
University of Oxford,
Parks Road,
Oxford OX1 3PJ, UK
e-mail: salvador.luque@imdea.org

T. V. Jones, T. Povey

Department of Engineering Science,
University of Oxford,
Parks Road,
Oxford OX1 3PJ, UK

1Present address: Unit of High Temperature Processes, IMDEA Energy Institute, Avenida Ramón de la Sagra, 3, Móstoles 28935, Spain.

2Corresponding author.

Manuscript received January 20, 2017; final manuscript received May 10, 2017; published online July 19, 2017. Assoc. Editor: Ardeshir (Ardy) Riahi.

J. Turbomach 139(11), 111005 (Jul 19, 2017) (11 pages) Paper No: TURBO-17-1011; doi: 10.1115/1.4037029 History: Received January 20, 2017; Revised May 10, 2017

This paper describes the effects of coolant-to-mainstream density ratio and specific heat capacity flux ratio (the product of blowing ratio and specific heat capacity ratio) on the overall cooling effectiveness of high pressure (HP) turbine vanes. Experimental measurements have been conducted at correct engine-matched conditions of Mach number, Reynolds number, turbulence intensity, and coolant-to-mainstream momentum flux ratio. Vanes tested were fully cooled production parts from an engine currently in service. A foreign gas mixture of SF6 and Ar was selected for injection as coolant in the facility so that density and blowing ratios were also matched to the engine situation. The isentropic exponent of the foreign gas mixture coincides with that of air. Full-coverage surface maps of overall cooling effectiveness were acquired by an infrared (IR) thermography technique at a range of mainstream-to-coolant temperature ratios. Measurements were subsequently scaled to engine conditions by employing a new theory based on the principle of superposition and a recovery and redistribution temperature demonstrated in previous papers. It is shown that the two aerodynamically matched situations of air- and foreign-gas-cooled experiments give virtually the same effectiveness trends and patterns. Actual levels differ, however, on account of specific heat capacity flux ratio differences. The effect is described and quantified by a one-dimensional analytical model of the vane wall. Differences in Biot number with respect to engine conditions are discussed as they also influence the scaling of turbine metal temperatures.

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References

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Figures

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Fig. 1

Cooling configuration of the HP turbine NGV, schematic sketch adapted from an original in Ref. [17]

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Fig. 2

Overhead photograph of the Annular Sector Heat Transfer Facility, including the foreign gas injection system

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Fig. 3

Coolant-to-mainstream total pressure ratio in the three manifolds of the Annular Sector Heat Transfer Facility

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Fig. 4

Full-coverage surface map of overall cooling effectiveness for the HP NGV in air-cooled tests

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Fig. 5

Full-coverage surface map of overall cooling effectiveness for the HP NGV in FG-cooled tests

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Fig. 6

Differences in overall cooling effectiveness between air- and FG-cooled experiments

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Fig. 7

Full-coverage surface map of recovery and redistribution parameter for the HP NGV in air-cooled tests

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Fig. 8

Full-coverage surface map of recovery and redistribution parameter for the HP NGV in FG-cooled tests

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Fig. 9

Differences in recovery and redistribution parameter between air- and FG-cooled experiments

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Fig. 10

Midspan distributions of overall cooling effectiveness for air- and FG-cooled experiments

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Fig. 11

Midspan distributions of ℜ for air- and FG-cooled tests, and conventional Tr/T01 ratios (based on external Mach numbers) for laminar and turbulent boundary layers

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Fig. 12

Schematic of the turbine vane heat transfer model

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Fig. 13

First-order correction of overall cooling effectiveness as a function of specific heat capacity ratio

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