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TECHNICAL PAPERS

# The Effects of a Trip Wire and Unsteadiness on a High-Speed Highly Loaded Low-Pressure Turbine Blade

[+] Author and Article Information
M. Vera, H. P. Hodson

Whittle Laboratory, University of Cambridge, Cambridge, UK

R. Vazquez

ITP, Industria de Turbopropulsores, Madrid, Spain

For simplicity, it is considered that $t∕τ0=0$ is when the center of the wake is at $70%S0$.

J. Turbomach 127(4), 747-754 (Mar 01, 2004) (8 pages) doi:10.1115/1.1934446 History: Received October 01, 2003; Revised March 01, 2004

## Abstract

This paper presents the effect of a single spanwise two-dimensional wire upon the downstream position of boundary layer transition under steady and unsteady inflow conditions. The study is carried out on a high turning, high-speed, low pressure turbine (LPT) profile designed to take account of the unsteady flow conditions. The experiments were carried out in a transonic cascade wind tunnel to which a rotating bar system had been added. The range of Reynolds and Mach numbers studied includes realistic LPT engine conditions and extends up to the transonic regime. Losses are measured to quantify the influence of the roughness with and without wake passing. Time resolved measurements such as hot wire boundary layer surveys and surface unsteady pressure are used to explain the state of the boundary layer. The results suggest that the effect of roughness on boundary layer transition is a stability governed phenomena, even at high Mach numbers. The combination of the effect of the roughness elements with the inviscid Kelvin–Helmholtz instability responsible for the rolling up of the separated shear layer (Stieger, R. D., 2002, Ph.D. thesis, Cambridge University) is also examined. Wake traverses using pneumatic probes downstream of the cascade reveal that the use of roughness elements reduces the profile losses up to exit Mach numbers of 0.8. This occurs with both steady and unsteady inflow conditions.

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## Figures

Figure 1

Cross section (left) and rear view (right) of the high speed bar rotating rig

Figure 2

Hot wire calibration map

Figure 3

Figure 4

Figure 5

Figure 6

Contours of ensemble averaged velocity on smooth surface (top) and with the trip at 60%S0 (bottom). Steady inflow. M3=0.61, Re3=1.3×105.

Figure 7

Shape factor at different snapshots for the cases of a smooth surface and trip at 60%S0. M3=0.61, Re3=1.3×105. fr=0.48.

Figure 8

Contours of time mean velocity on smooth surface (top) and with the trip at 66%S0 (center) and with the trip at 60%S0 (bottom). Steady inflow. M3=0.74, Re3=1.3×105.

Figure 9

rms of the unsteady pressure measurements as fractions of the exit dynamic pressure. Re3=1.3×105. Steady inflow.

Figure 10

Ensemble averaged unsteady pressure, raw pressure and rms as fractions of the exit dynamic pressure. M3=0.61, Re3=1.3×105. Streamwise location 85%S0. Unsteady inflow, fr=0.48.

Figure 11

Unsteady ensemble averaged pressure (top) and rms as a fraction of exit dynamic pressure (bottom) for the case of smooth surface and trip at 60%S0. M3=0.74, Re3=1.3×105. Streamwise location 85%S0. Unsteady inflow, fr=0.40.

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