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Research Papers

Investigation of Nonaxisymmetric Endwall Contouring and Three-Dimensional Airfoil Design in a 1.5-Stage Axial Turbine—Part I: Design and Novel Numerical Analysis Method

[+] Author and Article Information
Thorsten Poehler

Institute of Jet Propulsion and Turbomachinery,
RWTH Aachen University,
Templergraben 55,
Aachen 52062, Germany
e-mail: thorsten.poehler@man.eu

Jens Niewoehner, Peter Jeschke

Institute of Jet Propulsion and Turbomachinery,
RWTH Aachen University,
Templergraben 55,
Aachen 52062, Germany

Yavuz Guendogdu

MTU Aero Engines AG,
Dachauer Strasse 665,
Munich 80955, Germany

Shown in Part II of the paper.

1Present address: MAN Diesel & Turbo SE, Steinbrinkstr. 1, Oberhausen 46145, Germany.

2Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received November 20, 2014; final manuscript received December 11, 2014; published online February 3, 2015. Editor: Ronald Bunker.

J. Turbomach 137(8), 081009 (Aug 01, 2015) (11 pages) Paper No: TURBO-14-1301; doi: 10.1115/1.4029476 History: Received November 20, 2014; Revised December 11, 2014; Online February 03, 2015

This paper presents the results of the analysis of different 3D designs for the first stator and the rotor of a 1.5-stage turbine test rig. A tangential endwall contouring for the hub and the shroud, a bowed profile stacking, and a combination of those have been designed for the first stator. In addition, a tangential endwall contouring has been designed for the hub of the unshrouded rotor. Part I of this two-part paper deals with the design process and the numerical analysis of the results. All designs have been optimized using the stage efficiency as target function. For the design of the 3D stator vanes, the optimization led to an unexpected result: The secondary flow vortex strength increased. However, the secondary flow pattern is rearranged by the 3D-designing, leading to a smoother radial exit flow angle distribution. A subsequent reduction of the rotor losses overcompensates the higher stator losses. In order to understand how the 3D vanes affect the stator secondary flow pattern, a detailed analysis of vortex stretching and vortex dissipation is presented in this paper. With this approach, the various impacts of the 3D designs on the secondary flow vortices' strength can be quantified. In addition, the potential theory effect of the self-induced velocity is introduced here in order to explain the effects of a tangential endwall contouring on the trajectory of the pressure side leg of the horseshoe vortex (HVps). To the best of our knowledge, both approaches are new for the analysis of turbine secondary flows. The impact of the stronger but rearranged stator secondary flow on the rotor secondary loss development is analyzed by means of unsteady simulations. The results show that the rotor secondary flow can be effectively reduced through a proper stator secondary flow pattern. In Part II of this paper, the analysis of extensive experimental results validates and supplements the numerical analysis.

Copyright © 2015 by ASME
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References

Figures

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Fig. 1

Secondary flow model of a stator vane

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Fig. 2

Self-induced velocity of a vortex near a wall

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Fig. 3

Design parameter for bow (left) and endwall contouring (right)

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Fig. 4

Impact of the exit flow angle of bscV1 on stage efficiency (V1 stagger angle variation)

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Fig. 5

3D endwall designs: (a) f3dV1 design at hub, (b) f3dV1 design at shroud, and (c) ewcB1 design at hub

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Fig. 6

Visualization of the effects of endwall contouring and stator bowing by means of static pressure distributions and streamwise vorticity at the hub of V1. (a) bscV1 design. (b) f3dV1 design.

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Fig. 7

Axial distribution of the wall distance and the vortex stretching of the HVps at the hub. (a) Wall distance. (b) Vortex stretching (ω·∇)c.

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Fig. 8

Local coordinate system

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Fig. 9

Axial distribution of the pressure gradient (∂p/∂q) at 5% normalized passage height. (a) bscV1 versus ewcV1. (b) bscV1 versus bowV1. (c) bscV1 versus f3dV1.

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Fig. 10

Visualization of the effects of endwall contouring and stator bowing by means of static pressure distributions and streamwise vorticity at the shroud of V1. (a) bscV1 design. (b) f3dV1 design.

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Fig. 11

Axial distribution of streamwise vorticity, vortex stretching, and vortex dissipation of the HVps at the shroud. (a) Streamwise vorticity. (b) Vortex stretching (ω·∇)c. (c) Vortex dissipation ∂ω/∂t=1/ρ∇×(∇·¯¯τ).

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Fig. 12

Axial distribution of the pressure gradient (∂p/∂q) at 95% normalized passage height. (a) bscV1 versus ewcV1. (b) bscV1 versus bowV1. (c) bscV1 versus f3dV1.

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Fig. 13

Secondary flow in the rotor passage at xn,B1 = 5%, visualized by streamwise vorticity. (a) bscV1/bscB1 design. (b) f3dV1/bscB1 design.

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Fig. 14

Secondary flow in the rotor passage at xn,B1 = 90%, visualized by streamwise vorticity. (a) bscV1/bscB1 design. (b) f3dV1/bscB1 design.

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Fig. 15

Change of streamwise vorticity of a stator secondary flow vortex in a rotor passage (from Walraevens [25])

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