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Research Papers

Improved Methodologies for Time-Resolved Heat Transfer Measurements, Demonstrated on an Unshrouded Transonic Turbine Casing

[+] Author and Article Information
Matthew Collins

Osney Thermofluids Laboratory,
Department of Engineering Science,
University of Oxford,
Oxford OX1 3PJ, UK
e-mail: matthew.collins@eng.ox.ac.uk

Kam Chana

Osney Thermofluids Laboratory,
Department of Engineering Science,
University of Oxford,
Oxford OX1 3PJ, UK
e-mail: kam.chana@eng.ox.ac.uk

Thomas Povey

Osney Thermofluids Laboratory,
Department of Engineering Science,
University of Oxford,
Oxford OX1 3PJ, UK
e-mail: thomas.povey@eng.ox.ac.uk

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received February 24, 2016; final manuscript received March 9, 2016; published online May 17, 2016. Editor: Kenneth C. Hall.

J. Turbomach 138(11), 111007 (May 17, 2016) (10 pages) Paper No: TURBO-16-1051; doi: 10.1115/1.4033267 History: Received February 24, 2016; Revised March 09, 2016

Abstract

The high pressure (HP) rotor tip and over-tip casing are often life-limiting features in the turbine stages of current gas turbine engines. This is due to the high thermal load and high temperature cycling at both low and high frequencies. In the last few years, there have been numerous studies of turbine tip heat transfer. Comparatively fewer studies have considered the over-tip casing heat transfer. This is in part, no doubt, due to the more onerous test facility requirements to validate computational simulations. Because the casing potential field is dominated by the passing rotor, to perform representative over-tip measurements a rotating experiment is an essential requirement. This paper details the measurements taken on the Oxford turbine research facility (OTRF), an engine-scale rotating turbine facility which replicates engine-representative conditions of Mach number, Reynolds number, and gas-to-wall temperature ratio. High density arrays of miniature thin-film heat-flux gauges were used with a spatial resolution of 0.8 mm and temporal resolution of ∼120 kHz. The small size of the gauges, the high frequency response, and the improved processing methods allowed very detailed measurements of the heat transfer in this region. Time-resolved measurements of $TAW$ and $Nu$ are presented for the casing region (−30% to +125% $CAX$) and compared to other results in the literature. The results provide an almost unique data set for calibrating computational fluid dynamics (CFD) tools for heat transfer prediction in this highly unsteady environment dominated by the rotor over-tip flow.

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Figures

Fig. 1

Schematic of OTRF

Fig. 2

Experimental hardware installed in cassette

Fig. 3

Instrumented casing region with 92 TFHFGs

Fig. 4

Work process for measuring, recording, and processing heat transfer data using new HTA

Fig. 5

Schematic of wall heating/cooling hardware

Fig. 6

Plots of measured inlet total pressure (a) and total temperature measured local to the rotor casing (b)

Fig. 7

Plots of low pass filtered (2 kHz) measured TW (a) and q˙ calculated using impulse response (b) from a TFHFG during a run

Fig. 8

Regression performed on one TFHFG for one run, with a q˙ versus TW regression (a) and a regression against corrected TW′ (b)

Fig. 9

Plot of floating regression performed on multiple runs with different initial wall temperatures

Fig. 10

Time-averaged plots of TAW (a) and Nu (b) for 8 runs compared to experimental and CFD results obtained by Qureshi et al. [8]

Fig. 11

Schematic illustrating unsteady data processing to extract and TAW and HTC as functions of rotor pitch

Fig. 12

Time-resolved experimental measurements of rotor casing unsteady heat flux (a), TAW (b) and Nu (c)

Fig. 13

Over tip leakage flow relative to the rotor over a thick and thin blade

Fig. 14

Tip leakage vortex development over flat tip, Mischo et al. [33]

Fig. 15

TAW (a) and Nu (b) 95% confidence intervals as a proportion of measured value obtained from regression

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