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TECHNICAL PAPERS

Experimental Investigation of Turbine Leakage Flows on the Three-Dimensional Flow Field and Endwall Heat Transfer

[+] Author and Article Information
Hans-Jürgen Rehder, Axel Dannhauer

 Institute of Propulsion Technology, Turbine Technology, German Aerospace Center (DLR), 37073 Göttingen, Germany

J. Turbomach 129(3), 608-618 (Jul 20, 2006) (11 pages) doi:10.1115/1.2720484 History: Received July 14, 2006; Revised July 20, 2006

Within a European research project, the tip endwall region of low pressure turbine guide vanes with leakage ejection was investigated at DLR in Göttingen. For this purpose a new cascade wind tunnel with three large profiles in the test section and a contoured endwall was designed and built, representing 50% height of a real low pressure turbine stator and simulating the casing flow field of shrouded vanes. The effect of tip leakage flow was simulated by blowing air through a small leakage gap in the endwall just upstream of the vane leading edges. Engine relevant turbulence intensities were adjusted by an active turbulence generator mounted in the test section inlet plane. The experiments were performed with tangential and perpendicular leakage ejection and varying leakage mass flow rates up to 2%. Aerodynamic and thermodynamic measurement techniques were employed. Pressure distribution measurements provided information about the endwall and vane surface pressure field and its variation with leakage flow. Additionally streamline patterns (local shear stress directions) on the walls were detected by oil flow visualization. Downstream traverses with five-hole pyramid type probes allow a survey of the secondary flow behavior in the cascade exit plane. The flow field in the near endwall area downstream of the leakage gap and around the vane leading edges was investigated using a 2D particle image velocimetry system. In order to determine endwall heat transfer distributions, the wall temperatures were measured by an infrared camera system, while heat fluxes at the surfaces were generated with electric operating heating foils. It turned out from the experiments that distinct changes in the secondary flow behavior and endwall heat transfer occur mainly when the leakage mass flow rate is increased from 1% to 2%. Leakage ejection perpendicular to the main flow direction amplifies the secondary flow, in particular the horseshoe vortex, whereas tangential leakage ejection causes a significant reduction of this vortex system. For high leakage mass flow rates the boundary layer flow at the endwall is strongly affected and seems to be highly turbulent, resulting in entirely different heat transfer distributions.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 4

Leakage gap geometries

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Figure 5

Heat transfer measurement setup

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Figure 6

Inlet sidewall boundary layer

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Figure 7

Oil flow visualization on sidewall and vane suction side (zero leakage flow)

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Figure 8

Oil flow visualization on sidewall and vane suction side (tangential leakage ejection)

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Figure 9

Oil flow visualization on sidewall and vane suction side (perpendicular leakage ejection)

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Figure 10

Sidewall isentropic Mach number distributions

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Figure 11

Velocity vectors and Mach number contours at 5mm distance from the sidewall (zero leakage flow)

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Figure 12

Near wall 3D streamlines calculated from PIV measurements

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Figure 13

Velocity vectors, total pressure, and vorticity contours in the exit flow field (zero leakage flow)

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Figure 14

Velocity vectors, total pressure, and vorticity contours in the exit flow field (tangential leakage ejection)

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Figure 15

Velocity vectors, total pressure, and vorticity contours in the exit flow field (perpendicular leakage ejection)

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Figure 1

Typical shroud geometries in a low pressure turbine

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Figure 2

Vertical test section (cascade) geometry

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Figure 3

Horizontal test section geometry

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Figure 16

Spanwise distributions of energy loss coefficient

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Figure 17

Sidewall heat transfer distributions

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