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Research Papers

A Low Pressure Turbine With Profiled Endwalls and Purge Flow Operating With a Pressure Side Bubble

[+] Author and Article Information
P. Jenny1

 Laboratory for Energy Conversion, Department of Mechanical and Process Engineering, ETH Zurich, Zurich, 8092, Switzerlandjenny@lec.mavt.ethz.ch

R. S. Abhari

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

M. G. Rose

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

M. Brettschneider, J. Gier

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

1

Corresponding author.

J. Turbomach 134(6), 061038 (Sep 17, 2012) (9 pages) doi:10.1115/1.4006303 History: Received July 25, 2011; Revised July 27, 2011; Published September 17, 2012

This paper presents an experimental and computational study of non-axisymmetric rotor endwall profiling in a low pressure turbine. Endwall profiling has been proven to be an effective technique to reduce both turbine blade row losses and the required purge flow. For this work, a rotor with profiled endwalls on both hub and shroud is considered. The rotor tip and hub endwalls have been designed using an automatic numerical optimization that is implemented in an in-house MTU code. The endwall shape is modified up to the platform leading edge. Several levels of purge flow are considered in order to analyze the combined effects of endwall profiling and purge flow. The non-dimensional parameters match real engine conditions. The 2-sensor Fast Response Aerodynamic Probe (FRAP) technique system developed at ETH Zurich is used in this experimental campaign. Time-resolved measurements of the unsteady pressure, temperature and entropy fields between the rotor and stator blade rows are made. For the operating point under investigation, the turbine rotor blades have pressure side separations. The unsteady behavior of the pressure side bubble is studied. Furthermore, the results of unsteady RANS simulations are compared to the measurements and the computations are also used to detail the flow field with particular emphasis on the unsteady purge flow migration and transport mechanisms in the turbine main flow containing a rotor pressure side separation. The profiled endwalls show the beneficial effects of improved measured efficiency at this operating point, together with a reduced sensitivity to purge flow.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Illustration of leakage path

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Figure 2

Non-axisymmetric endwall shapes from the optimization

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Figure 3

Illustration of geometrical relations and measurement planes

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Figure 4

Comparison between measured and simulated relative flow yaw angle at rotor exit for the nominal injection rate (IR = 0.8%)

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Figure 5

Comparison of normalized total pressure (=Pt /Pt,in ) in rotor frame of reference for prediction and experiment at the rotor exit at the nominal injection rate IR = 0.8%

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Figure 6

Normalized total to total efficiency as a function of injected purge flow for computation and measurements with error estimation

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Figure 7

Radial distribution of circumferentially mass and time-averaged measured relative flow yaw angle at rotor exit as a function of injection rate

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Figure 8

Time-averaged area plot in rotor relative frame of reference at rotor exit. The parameter is the experimental rms of the rotor relative total pressure Pt,rel (Pa).

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Figure 9

Time-averaged area plot in rotor relative frame of reference at rotor exit. The parameter is the streamwise vorticity ΩS (1/s).

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Figure 10

Time space plot of the experimental rms of the total pressure (Pa) at 60% span

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Figure 11

Iso-surfaces of zero axial velocity on the rotor blade pressure side during one period T corresponding to two stator pitches. The black rectangle in Fig. 1 defines the view of each subfigure.

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Figure 12

Particle tracks of particles released inside pressure side bubble, IR = 0.8%. The color of the particles indicates the relative velocity (m/s).

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Figure 13

Contour plot of normalized reduced static pressure (=Pred /Pt,in ) on the rotor blade for nominal injection rate

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Figure 14

Iso-surfaces of zero axial velocity on the rotor blade pressure side for three different injection levels but at the same phase in the cycle

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Figure 15

Circumferentially area and time-averaged measured static pressure coefficient (=Ps /Pt,in ) and change of incidence between nominal injection rate (IR = 0.8%) and the lowest injection rate (IR = 0.4%) and the maximum injection rate (IR = 1.2%) and the lowest injection rate at rotor inlet

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