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Research Papers

Blade Lean and Shroud Leakage Flows in Low Aspect Ratio Turbines

[+] Author and Article Information
Budimir Rosic

 Whittle Laboratory, 1 JJ Thomson Avenue, CB3 ODY Cambridge, UKbr241@cam.ac.uk

Liping Xu

 Whittle Laboratory, 1 JJ Thomson Avenue, CB3 ODY Cambridge, UK

J. Turbomach 134(3), 031003 (Jul 14, 2011) (12 pages) doi:10.1115/1.3106002 History: Received November 26, 2008; Revised December 04, 2008; Published July 14, 2011; Online July 14, 2011

Blade lean, i.e., nonradial blade stacking, has been intensively used over the past in the design process of low aspect ratio gas and steam turbines. Although its influence on turbine efficiency is not completely understood, it has been proved as an effective way of controlling blade loading and secondary flows on blade passage endwalls. Three-dimensional blade designs in modern industrial practice are usually carried out using clean endwalls. The influence of the leakage flows on three-dimensional blade design is traditionally neglected. This paper presents an experimental study where two different stator blades, with different levels of compound lean, were tested in a low speed three-stage model turbine with the shroud leakage flow geometry representative of industrial practice. The experimental measurements were compared with numerical tests, conducted on the same blade geometries. The influence of the compound lean on the stator flow field was analyzed in detail. In order to analyze the combined effects of both the stator hub and the rotor shroud leakage flow on the blade lean, in the second part of the paper a numerical study on a two stage turbine with both leakage flow paths representative of a real turbine was carried out. Performance of three different stator blade designs (two different levels of compound lean and a straight blade) was investigated. The aim of this study is to understand the mechanism and the consequence of the stator blade lean on stage performance in an environment with leakage flows and associated cavities.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of model turbine

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Figure 2

Computational mesh and grid details (every two nodes in the span- and streamwise directions)

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Figure 3

Three stator blades with different radial stackings

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Figure 4

Static pressure distribution at 40% blade axial chord for the straight blade (S) and high compound lean blade (XL)

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Figure 5

Stator blade surface pressure distribution (blade XL)

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Figure 6

Stator blade surface pressure distribution (blade L)

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Figure 7

Stator blade surface pressure distribution (blade S)

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Figure 8

Predicted streamlines on the suction side and hub blade to blade plane

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Figure 9

Predicted streamwise vorticity overlayed over total pressure line contours for leaned (XL) and straight blade (S) at axial location 110% Cx

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Figure 10

Streamwise vorticity contours at two different axial locations (90% Cx and 110% Cx) for straight blade (S)

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Figure 11

Streamwise vorticity contours at two different axial locations (90% Cx and 110% Cx) for leaned blade (XL)

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Figure 12

Streamline shift from axial direction on the suction side and pressure side for straight blade (S)

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Figure 13

Streamline shift from axial direction on the suction and pressure sides for compound leaned blade (XL)

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Figure 14

Measured and predicted pitchwise averaged yaw angles

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Figure 15

Measured and predicted total pressure coefficient Cp0,T contours downstream of stator 1

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Figure 16

Measured and predicted total pressure coefficient Cp0,T contours downstream of stator 3

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Figure 17

Predicted change in efficiency for different compound lean angles

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Figure 18

Predicted transfer of tangential vorticity downstream of stator 1: (a) across the mixing plane, and (b) across the sliding plane (time averaged relative to the rotor inlet)

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Figure 19

Computational flow domain together with the rotor shroud and stator shroud geometry details

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Figure 20

Predicted yaw angle downstream of stators 1 and 2 (clean endwalls)

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Figure 21

Predicted relative yaw angle downstream of rotors 1 and 2 (clean endwalls)

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Figure 22

Streamwise vorticity overlayed over total pressure line contours for high compound lean (XL) and straight blade (S) at axial location 110% Cx with stator hub leakage flow

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Figure 23

Predicted yaw angle (both stator and rotor shroud leakage flow paths included)

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Figure 24

Predicted relative yaw angle (both stator and rotor shroud leakage flow paths included)

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Figure 25

Influence of stator blade lean on turbine performance for four different stage geometries

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