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Research Papers

# Transonic Turbine Blade Tip Aerothermal Performance With Different Tip Gaps—Part I: Tip Heat Transfer

[+] Author and Article Information
Q. Zhang, D. O. O’Dowd, L. He, M. L. G. Oldfield, P. M. Ligrani

Department of Engineering Science, University of Oxford, Osney Mead, Oxford OX2 0ES, UK

J. Turbomach 133(4), 041027 (Apr 27, 2011) (9 pages) doi:10.1115/1.4003063 History: Received July 11, 2010; Revised July 22, 2010; Published April 27, 2011; Online April 27, 2011

## Abstract

A closely combined experimental and computational fluid dynamics (CFD) study on a transonic blade tip aerothermal performance at engine representative Mach and Reynolds numbers $(Mexit=1,Reexit=1.27×106)$ is presented here and its companion paper (Part II). The present paper considers surface heat-transfer distributions on tip surfaces and on suction and pressure-side surfaces (near-tip region). Spatially resolved surface heat-transfer data are measured using infrared thermography and transient techniques within the Oxford University high speed linear cascade research facility. The Rolls-Royce PLC HYDRA suite is employed for numerical predictions for the same tip configuration and flow conditions. The CFD results are generally in good agreement with experimental data and show that the flow over a large portion of the blade tip is supersonic for all three tip gaps investigated. Mach numbers within the tip gap become lower as the tip gap decreases. For the flow regions near the leading edge of the tip gap, surface Nusselt numbers decrease as the tip gap decreases. Opposite trends are observed for the trailing edge region. Several “hot spot” features on blade tip surfaces are attributed to enhanced turbulence thermal diffusion in local regions. Other surface heat-transfer variations are attributed to flow variations induced by shock waves. Flow structure and surface heat-transfer variations are also investigated numerically when a moving casing is present. The inclusion of moving casing leads to notable changes to flow structural characteristics and associated surface heat-transfer variations. However, significant portions of the tip leakage flow remain transonic with clearly identifiable shock wave structures.

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## Figures

Figure 1

The schematic of the Oxford high speed linear cascade research facility

Figure 2

Schematic diagrams of the test section: (a) side view and (b) tip view

Figure 3

Infrared camera in situ calibration data

Figure 4

An example of heat flux versus temperature history for one location on the tip surface

Figure 5

Computational domain and mesh employed in the present study

Figure 6

Tip Nusselt number contours for three tip gaps investigated (experimental data)

Figure 7

Tip Nusselt number contours for three tip gaps investigated (HYDRA prediction)

Figure 8

Circumferential-averaged Nusselt numbers along the axial chord for experimental data and HYDRA prediction

Figure 9

Local tip Mach number distribution for different tip gaps (HYDRA prediction)

Figure 10

Tip surface heat flux (W/m2) and X-components of density gradient (kg/m2) distributions on four cut planes (HYDRA prediction)

Figure 11

Turbulent to laminar viscosity ratio (μT/μL) distributions above the tip surface for a tip gap g/S=1.0% (HYDRA prediction)

Figure 12

Nusselt number on the suction side (experimental data)

Figure 13

Nusselt number on the suction side (HYDRA prediction)

Figure 14

Total pressure ratio contour Po/Poi along a streamwise cut plane for three tip gaps (HYDRA prediction)

Figure 15

Nusselt number on the pressure side for 1.0% tip gap

Figure 16

Local tip Mach number distributions for a tip gap of 1.0% with and without moving casing (HYDRA prediction) (solid black line corresponds to Mach number of 1)

Figure 17

Nusselt number contours for a tip gap of 1.0% with and without moving casing (HYDRA prediction)

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