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Research Papers

# Improving Efficiency of a High Work Turbine Using Nonaxisymmetric Endwalls— Part I: Endwall Design and Performance

[+] Author and Article Information
T. Germain

MTU Aero Engines GmbH, Dachauer Strasse 665, 80995 München, Germanythomas.germain@muc.mtu.de

M. Nagel, I. Raab

MTU Aero Engines GmbH, Dachauer Strasse 665, 80995 München, Germany

P. Schüpbach, R. S. Abhari

Department of Mechanical and Process Engineering, LEC, Laboratory of Energy Conversion, ETH Zurich, 8092 Zurich, Switzerland

M. Rose

Institute of Aeronautical Propulsion, University of Stuttgart, 70569 Stuttgart, Germany

J. Turbomach 132(2), 021007 (Jan 12, 2010) (9 pages) doi:10.1115/1.3106706 History: Received January 26, 2009; Revised February 10, 2009; Published January 12, 2010; Online January 12, 2010

## Abstract

This paper is the first part of a two part paper reporting the improvement of efficiency of a one-and-half stage high work axial flow turbine by nonaxisymmetric endwall contouring. In this first paper the design of the endwall contours is described, and the computational fluid dynamics (CFD) flow predictions are compared with five-hole-probe measurements. The endwalls have been designed using automatic numerical optimization by means of a sequential quadratic programming algorithm, the flow being computed with the 3D Reynolds averaged Navier-Stokes (RANS) solver TRACE . The aim of the design was to reduce the secondary kinetic energy and secondary losses. The experimental results confirm the improvement of turbine efficiency, showing a stage efficiency benefit of $1%±0.4%$, revealing that the improvement is underestimated by CFD. The secondary flow and loss have been significantly reduced in the vane, but improvement of the midspan flow is also observed. Mainly this loss reduction in the first row and the more homogeneous flow is responsible for the overall improvement. Numerical investigations indicate that the transition modeling on the airfoil strongly influences the secondary loss predictions. The results confirm that nonaxisymmetric endwall profiling is an effective method to improve turbine efficiency but that further modeling work is needed to achieve a good predictability.

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## Figures

Figure 1

Schematic view of secondary flow structures in a turbine, after Langston (2)

Figure 2

Cross section of the LISA turbine

Figure 3

Parametrization of the nonaxisymmetric endwalls

Figure 4

Figure 5

Nonaxisymmetric endwall shapes of (a) stator 1 hub, (b) stator 1 tip, and (c) rotor 1 hub

Figure 6

Pitchwise averaged loss, yaw angle, and SKE at the stator 1 exit

Figure 7

2D Loss distribution at the stator 1 exit: (a) baseline and (b) contoured

Figure 8

Endwall pressure on the S1 hub: (a) CFD baseline, (b) CFD contoured, and (c) experimental contoured

Figure 9

Pitchwise averaged relative total pressure and yaw angle at the rotor R exit

Figure 10

Wall p, flow pt, and vortex strength on four different planes within the passage

Figure 11

S1 airfoil static pressure prediction at 5%, 50%, and 95% spans: _ _ baseline and __ contoured

Figure 12

Predicted S1 suction side wall streamline patterns with pressure contours for (a) the baseline and (b) the contoured case

Figure 13

Pitchwise averaged loss, experimental, and CFD for different fillet configurations

Figure 14

Pitchwise averaged loss, experimental, and CFD for different transition model setups

Figure 15

Pitchwise averaged loss, experimental, and CFD for different inlet turbulence levels

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