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Research Papers

Effect of Hot Streak Migration on Unsteady Blade Row Interaction in an Axial Turbine

[+] Author and Article Information
P. Jenny1

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

C. Lenherr, R. S. Abhari

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

A. Kalfas

LFMT, Department of Mechanical Engineering,  Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece

1

Corresponding author.

J. Turbomach 134(5), 051020 (May 29, 2012) (9 pages) doi:10.1115/1.4004447 History: Received March 16, 2011; Accepted June 03, 2011; Published May 29, 2012; Online May 29, 2012

This paper presents an experimental study of the effect of unsteady blade row interaction on the migration of hot streaks in an axial turbine. The hot streaks can cause localized hot spots on the blade surfaces in a high-pressure turbine, leading to high heat loads and potentially catastrophic failure of the blades. An improved understanding of the effect of unsteady blade row interaction on an inlet temperature distortion is of crucial importance. The impact of hot streaks on the aerodynamic performance of a turbine stage is also not well understood. In the current experiment, the influence of hot streaks on a highly loaded 1.5-stage unshrouded model axial turbine is studied. A hot streak generator has been developed specifically for this project to introduce hot streaks that match the dimensional parameters of real engines. The temperature profile, spanwise position, circumferential position, and cross-section shape of the hot streak can be independently varied. The recently developed ETH Zurich two-sensor high temperature (260 °C) fast response aerodynamic probe (FRAP) technique and the fast response entropy. Probe (FENT) systems are used in this experimental campaign. Time resolved measurements of the unsteady pressure, temperature, and entropy are made at the NGV inlet and between the rotor and stator blade rows. From the nozzle guide vane inlet to outlet the measurements show a reduction in the maximum relative entropy difference between the free stream and the hot spot of 30% for the highest temperature gases in the core of the hot streak, indicating a region of heat loss. Time resolved flow field measurements at the rotor exit based on both measurement methods showed the hot gases traveling towards the hub and tip casing on the blade pressure side and interacting with secondary flows such as the hub passage vortex.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 9

Circumferentially mass and time averaged total entropy at NGV1 inlet and exit measurement plane for the two measurement cases

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Figure 10

Space time diagrams of rms signal at R1ex for two different span positions. On the left hand side without hot streak, on the right hand side with hot streak.

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Figure 11

Space time diagram of rms signal at R1ex

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Figure 12

Space time diagram of radial velocity Vr at R1ex

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Figure 13

Space time diagram of normalized stagnation temperature at R1ex

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Figure 1

Cut through the 1.5-stage unshrouded turbine with hot streak generator upstream of NGV1

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Figure 2

Illustration of geometrical relations and measurement planes

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Figure 3

Time averaged normalized total temperature at the NGV1 inlet with hot streak (Tpeak /Tfree stream  = 1.21)

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Figure 4

Circumferentially mass and time averaged normalized total temperature at the NGV1 inlet plane for the two measurement cases

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Figure 5

Comparison of circumferentially mass and time averaged normalized total temperature at the NGV1 inlet and exit planes for the two different test cases

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Figure 6

Normalized stagnation temperature for different time steps at traverse plane S1ex (Tpeak /Tfree stream  = 1.21)

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Figure 7

Time averaged normalized stagnation temperature at S1ex plane (Tpeak /Tfree stream  = 1.21)

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Figure 8

Time averaged total entropy at NGV1 inlet and outlet (Tpeak /Tfree stream  = 1.21)

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