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Research Papers

A Novel Technique for Assessing Turbine Cooling System Performance

[+] Author and Article Information
S. Luque, T. Povey

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

J. Turbomach 133(3), 031013 (Nov 15, 2010) (9 pages) doi:10.1115/1.4001232 History: Received August 19, 2009; Revised October 20, 2009; Published November 15, 2010; Online November 15, 2010

A new experimental technique for the accurate measurement of steady-state metal temperature surface distributions of modern heavily film-cooled turbine vanes has been developed and is described in this paper. The technique is analogous to the thermal paint test but has been designed for fundamental research. The experimental facility consists of an annular sector cascade of high pressure (HP) turbine vanes from a current production engine. Flow conditioning is achieved by using an annular sector of deswirl vanes downstream of the test section, being both connected by a three-dimensionally contoured duct. As a result, a transonic and periodic flow, highly representative of the engine aerodynamic field, is established: Inlet turbulence levels, mainstream Mach and Reynolds numbers, and coolant-to-mainstream total pressure ratio are matched. Since the fully three-dimensional nozzle guide vane (NGV) geometry is used, the correct radial pressure gradient and secondary flow development are simulated and the cooling flow redistribution is engine-realistic. To allow heat transfer measurements to be performed, a mainstream-to-coolant temperature difference (up to 33.5°C) is generated by using two steel-wire mesh heaters, operated in series. NGV surface metal temperatures are measured (between 20°C and 40°C) by wide-band thermochromic liquid crystals. These are calibrated in situ and on a per-pixel basis against vane surface thermocouples, in a heating process that spans the entire color play and during which the turbine vanes can be assumed to slowly follow a succession of isothermal states. Experimental surface distributions of overall cooling effectiveness are presented in this paper. By employing resin vanes of the same geometry and cooling configuration (to implement adiabatic wall thermal boundary conditions) and the transient liquid crystal technique, surface distributions of external heat transfer coefficient and film cooling effectiveness can be acquired. By combining these measurements with those from the metal vanes, the results can be scaled to engine conditions with a good level of accuracy.

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References

Figures

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Figure 1

Development of secondary flows in swirling flows, from Ref. 19

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Figure 2

Overhead photograph of the Oxford annular sector heat transfer facility

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Figure 3

2D schematic of the working section of the Oxford annular sector heat transfer facility

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Figure 4

Schematic sketch (not to scale) of the NGV cooling system

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Figure 5

Typical temperature histories during a run in the annular sector heat transfer facility

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Figure 6

View of the wide-band liquid crystals on the SS of the test vane at steady-state conditions

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Figure 7

Typical hue-temperature TLC calibration curves for two sets of 25 adjacent pixels on each vane surface

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Figure 8

Overall cooling effectiveness distributions over the HP NGV surfaces

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Figure 9

Midspan overall cooling effectiveness distribution on the HP NGV

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Figure 10

Absolute error in overall cooling effectiveness as a function of mainstream-to-coolant temperature difference and effectiveness itself

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Figure 11

Comparison of SS thermocouple and TLC temperature measurements

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