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Research Papers

# Turbine Blade Tip Heat Transfer in Low Speed and High Speed Flows

[+] Author and Article Information
Andrew P. S. Wheeler1

School of Engineering and Materials Science, Queen Mary, University of London, Mile End Road, London, E1 4NS, UKa.wheeler@qmul.ac.uk

Nicholas R. Atkins

Whittle Laboratory, University of Cambridge, Cambridge, CB3 0DY, UK

Li He

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

1

Corresponding author.

J. Turbomach 133(4), 041025 (Apr 26, 2011) (9 pages) doi:10.1115/1.4002424 History: Received February 11, 2010; Revised February 22, 2010; Published April 26, 2011; Online April 26, 2011

## Abstract

In this paper, high and low speed tip flows are investigated for a high-pressure turbine blade. Previous experimental data are used to validate a computational fluid dynamics (CFD) code, which is then used to study the tip heat transfer in high and low speed cascades. The results show that at engine representative Mach numbers, the tip flow is predominantly transonic. Thus, compared with the low speed tip flow, the heat transfer is affected by reductions in both the heat-transfer coefficient and the recovery temperature. The high Mach numbers in the tip region $(M>1.5)$ lead to large local variations in recovery temperature. Significant changes in the heat-transfer coefficient are also observed. These are due to changes in the structure of the tip flow at high speed. At high speeds, the pressure side corner separation bubble reattachment occurs through supersonic acceleration, which halves the length of the bubble when the tip-gap exit Mach number is increased from 0.1 to 1.0. In addition, shock/boundary-layer interactions within the tip gap lead to large changes in the tip boundary-layer thickness. These effects give rise to significant differences in the heat-transfer coefficient within the tip region compared with the low speed tip flow. Compared with the low speed tip flow, the high speed tip flow is much less dominated by turbulent dissipation and is thus less sensitive to the choice of turbulence model. These results clearly demonstrate that blade tip heat transfer is a strong function of Mach number, an important implication when considering the use of low speed experimental testing and associated CFD validation in engine blade tip design.

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## Figures

Figure 6

Predicted heat flux and Mach number contours and streamlines (Spalart–Allmaras+WF)

Figure 7

Isentropic Mach number distributions for blades A, B, and C

Figure 8

Predicted tip isentropic Mach number for blades A, B, and C (normalized by exit Mach number)

Figure 9

Predicted tip heat flux for blades A, B, and C (Tg/Tw=1.5)

Figure 10

Predicted variation in area-averaged tip heat load

Figure 11

Predicted adiabatic wall temperature and Nusselt number for blade A (Mexit=0.98, Tg/Tw=1.5)

Figure 12

Predicted turbulent to laminar viscosity ratio (μT/μL) for blades A and C, cut at 4% tip gap above tip surface

Figure 13

Mach number contours on a cut plane through the tip gap and surface heat-transfer contours for blades A and C (SAWF)

Figure 14

Width-to-gap ratio against axial chord blades A and C

Figure 15

Effect of width-to-gap ratio on quasi-three-dimensional tip flow (Mexit=0.9)

Figure 16

Effect of pressure ratio on quasi-three-dimensional tip flow (w/g=5)

Figure 17

Separation bubble height and length from the quasi-three-dimensional tip flow (w/g=5)

Figure 18

Effect of pressure ratio on turbulent viscosity (w/g=5)

Figure 19

Transonic tip flow Mach contours

Figure 4

Nusselt number distributions at midspan, comparison of CFD and experiment

Figure 5

Comparison of experimental and predicted blade tip heat flux with the mapping between experimental gauge locations and the CFD mesh

Figure 1

1 and 1/2 stage mesh (top) and typical cascade blade passage mesh (bottom)

Figure 2

Quasi-three-dimensional tip model mesh

Figure 3

Isentropic Mach number distributions at midspan, comparison of CFD and experiment

## Errata

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