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TECHNICAL PAPERS

Multistage Aspects and Unsteady Effects of Stator and Rotor Clocking in an Axial Turbine With Low Aspect Ratio Blading

[+] Author and Article Information
T. Behr

Turbomachinery Laboratory, Swiss Federal Institute of Technology, 8092 Zurich, Switzerlandbehr@lsm.iet.mavt.ethz.ch

L. Porreca, T. Mokulys, A. I. Kalfas, R. S. Abhari

Turbomachinery Laboratory, Swiss Federal Institute of Technology, 8092 Zurich, Switzerland

J. Turbomach 128(1), 11-22 (Jun 28, 2005) (12 pages) doi:10.1115/1.2101855 History: Received June 28, 2004; Revised June 28, 2005

This paper presents the outcome of a recent study in clocking-related flow features and multistage effects occurring in high-pressure turbine blade geometries. The current investigation deals with an experimentally based systematic analysis of the effects of both stator-stator and rotor-rotor clocking. Due to the low aspect ratio of the turbine geometry, the flow field is strongly three-dimensional and is dominated by secondary flow structures. The investigation aims to identify the flow interactions involved and the associated effects on performance improvement or degradation. Consequently a three-dimensional numerical analysis has been undertaken to provide the numerical background to the test case considered. The experimental studies were performed in a two-stage axial research turbine facility. The turbine provides a realistic multi-stage environment, in which both stator blade rows and the two rotors can be clocked relative to each other. All blade rows have the same blade number count, which tends to amplify clocking effects. Unsteady and steady measurements were obtained in the second stage using fast response aerodynamic probes and miniature pneumatic five-hole probes. The current comprehensive investigation has shown that multistage and unsteady flow effects of stator and rotor clocking in low aspect ratio turbines are combined in a nonlinear fashion caused by axial and radial redistribution of low energy fluid. The integral result of clocking on stage efficiency is compensated by competing loss generating mechanisms across the span.

Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

“LISA” Two stages axial turbine facility

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Figure 2

Relative circumferential stator-stator (SS) and rotor-rotor (RR) clocking positions in percent of circumferential chord. Position of measurement planes

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Figure 3

CFD—Mesh of “LISA” two-stage axial turbine configuration

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Figure 4

TC2—total pressure coefficient Cpt [−] downstream of Rotor 1 at eight different stator-stator positions at RR00 (coarse grid measurement, pneumatically averaged). (a) SS00, (b) SS12.5, (c) SS25, (d) SS37.5, (e) SS50, (f) SS62.5, (g) SS75, and (h) SS87.5.

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Figure 5

TC2—pitchwise distribution of absolute flow yaw angle downstream of rotor 1 at (a) 79% and (b) 23% span (eight stator clocking positions at RR00)

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Figure 6

TC2—time resolved pitchwise distribution of absolute flow yaw angle downstream of rotor 1 at 79% span (a) SS00RR00 and (b) SS50RR00

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Figure 7

Flow yaw angle distribution downstream of rotor 1 at (a) 0% and (b) 50% stator clocking (RR00)

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Figure 8

Difference of flow yaw angles between 50% and 0% Stator clocking (RR00) downstream of rotor 1. (a) Pitchwise distribution and (b) circumferentially massaveraged and spanwise distribution

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Figure 9

Difference between 50% and 0% rotor clocking in flow yaw angle distribution downstream of rotor 1 at (a) SS00 and (b) SS50

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Figure 10

Spanwise total pressure distribution downstream of rotor 1—comparison of CFD and experiment

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Figure 11

TC1, CFD—comparison of total pressure coefficient distribution of experiment and CFD downstream of rotor 1 at RR00. (a) SS00 (Exp.), (b) SS00 (CFD), (c) SS50 (Exp.), and (d) SS50 (CFD)

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Figure 12

CFD—static surface pressure distribution of stator 2 at 79% span for four different stator and rotor clocking cases

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Figure 13

Turning angle differences Δε across stator 2 of four clocking configurations (reference case is SS00RR00): (a) Experiment (TC1) and (b) CFD

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Figure 14

TC1—absolute flow angle differences Δϕ of four clocking configurations (reference case: SS00RR00) at stator 2 exit: (a) experiment (TC1) and (b) CFD

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Figure 15

TC2—time distance diagram of flow yaw angle downstream of stator 2, pitchwise massaverages spanwise distribution versus time: (a) SS00 and (b) SS50 at RR00

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Figure 16

TC2—measured static entropy difference across the second stator of (a) SS00 and (b) SS50 positions (both at RR00) and (c) corresponding pitchwise averaged spanwise distributions

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Figure 17

Relative turning angle differences Δε across rotor 2 of four clocking configurations (reference case is SS00RR00): (a) experiment (TC1) and (b) CFD

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Figure 18

TC2, CFD—relative thermodynamic efficiency difference to the reference case of three characteristic clocking configurations: (a) stage 1, (b) stage 2, and (c) turbine

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Figure 19

TC2—spanwise distribution of turbine relative thermodynamic efficiency difference to the reference case of three characteristic clocking configurations

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Figure 20

TC2—total-to-total mechanic efficiency of the second stage at eight stator and two rotor clocking positions

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Figure 21

CFD—overall aerodynamic loss deviation from reference case SS00 RR00

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Figure 22

CFD—aerodynamic loss deviation from reference case 0-0 clocking for each blade row: (a)) 2D and (b) 3D

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