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TECHNICAL PAPERS

# Unsteady Flow Physics and Performance of a One-and-$1∕2$-Stage Unshrouded High Work Turbine

[+] Author and Article Information
T. Behr

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

A. I. Kalfas

Deparment of Mechanical Engineering, Aristotle University of Thessaloniki, Greece

R. S. Abhari

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

J. Turbomach 129(2), 348-359 (Jun 08, 2006) (12 pages) doi:10.1115/1.2447707 History: Received June 07, 2006; Revised June 08, 2006

## Abstract

This paper presents an experimental study of the flow mechanisms of tip leakage across a blade of an unshrouded turbine rotor. It shows the design of a new one-and-$1∕2$-stage, unshrouded turbine configuration, which has been developed within the Turbomachinery Laboratory of ETH Zurich. This test case is a model of a high work $(Δh∕u2=2.36)$ axial turbine. The experimental investigation comprises data from unsteady and steady probe measurements, which has been acquired around all the bladerows of the one-and-$1∕2$-stage, unshrouded turbine. A newly developed 2-sensor Fast Response Aerodynamic Probe (FRAP) technique has been used in the current measurement campaign. The paper contains a detailed analysis of the unsteady interaction between rotor and stator blade rows, with particular attention paid on the flow in the blade tip region. It has been found that the interaction of the rotor and the downstream stator has an influence on the development of the tip leakage vortex of the rotor. The vortex is modulated by the stator profiles and shows variation in size and relative position to the rotor trailing edge when it stretches around the stator leading edge. Thereby a deflection of the tip leakage vortex has been observed, which expresses in a varying circumferential distance between two neighboring vortices of $±20%$ of a rotor pitch. Furthermore, a significant influence of quasi-stationary secondary flow features of the upstream stator row on the secondary flow of the rotor has been detected. The geometry and flow field data of the one-and-$1∕2$-stage turbine will be available to the turbomachinery community for validation and improvement of numerical tools.

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## Figures

Figure 1

“LISA” 11∕2 stage axial turbine facility

Figure 2

1.5-stage turbine section with probe measurement planes and tandem exit guide vane section

Figure 3

Rotor blisk of the 1.5-stage unshrouded turbine

Figure 4

Profile geometry of rotor blade at three span positions

Figure 5

Distribution of relative isentropic Mach numbers on the rotor at three span positions

Figure 6

Profile of first outlet guide vane row

Figure 7

Stacking definition of first OGV row

Figure 8

Smith chart with measured operating point and determined total-to-total efficiency (reproduced after Ref. 32)

Figure 9

Comparison of first OGV static pressure recovery between design and experiment

Figure 10

Distribution of measured total pressure at exit of stator 1 at the time instants of a rotor blade passing period: (a) t∕T=0.00; and (b) t∕T=0.50

Figure 11

Circumferentially mass-averaged distribution of measured relative flow yaw angle at exit of stator 1 versus time of three rotor blade passing periods

Figure 12

Circumferential distribution of measured relative flow yaw angle at exit of stator 1 at 83% span versus time of three rotor blade passing periods

Figure 13

Distribution of measured relative total pressure coefficient downstream of the rotor at four different rotor blade passing periods: (a) t∕T=0.00; (b) t∕T=0.25; (c) t∕T=0.50; and (d)t∕T=0.75

Figure 14

Circumferential distribution of relative total pressure coefficient versus time at rotor exit at 95% span

Figure 15

Circumferential distribution of measured relative mach number versus time at rotor exit at 95% span

Figure 16

Circumferential distance between the cores of two adjoining tip leakage vortices plotted versus time

Figure 17

Maximum and minimum deviation from time-averaged mean value of circumferentially mass-averaged spanwise distribution of relative flow yaw angles at rotor exit

Figure 18

Distribution of measured total pressure coefficient at the exit of stator 2 at rotor blade passing periods: (a) t∕T=0.00; and (b) t∕T=0.50

Figure 19

Circumferentially mass-averaged distribution of measured total pressure coefficients at exit of stator 2, plotted versus time of three rotor blade passing periods

Figure 20

Circumferentially mass-averaged distribution of measured absolute flow yaw angle at exit of stator 2, plotted versus time of three rotor blade passing periods

Figure 21

Comparison of relative exit flow angle behind the rotor between time-averaged experimental results and CFD

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