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Research Papers

Aerothermal Performance of Streamwise and Compound Angled Pulsating Film Cooling Jets

[+] Author and Article Information
Vipluv Aga

Department of Mechanical and Process Engineering, Institute for Energy Technologies, ETH Zurich, CH-8092 Zurich, Switzerlandvaga@ethz.ch

Michel Mansour, Reza S. Abhari

Department of Mechanical and Process Engineering, Institute for Energy Technologies, ETH Zurich, CH-8092 Zurich, Switzerland

J. Turbomach 131(4), 041015 (Jul 06, 2009) (11 pages) doi:10.1115/1.3072489 History: Received August 22, 2008; Revised August 31, 2008; Published July 06, 2009

The quantification of aerothermal loss is carried out for streamwise and compound angled film cooling jets with and without large scale pulsation. This paper reports on the simultaneous measurements of the unsteady pressure and temperature field of streamwise and a 60 deg compound angled film cooling jet, both with a 30 deg surface angle over a flat plate with no pressure gradients. Turbine representative nondimensionals in terms of the geometry and operating conditions are studied. The main flow is heated more than the injected flow to have a temperature difference and hence a density ratio of 1.3, while the blowing ratio is maintained at 2. The entropy change, derived from pressure and temperature measurements, is calculated by using modified reference conditions to better reflect the losses in both the jet and the freestream. The effects of the periodic unsteadiness associated with rotating machinery are simulated by pulsating the jets. These effects are documented through time-resolved entropy change contours. Mass-averaged entropy and kinetic energy loss coefficients seem to be apt quantities for comparing the aerothermal performance of streamwise and compound angled injections. It is observed that the mass-averaged entropy loss of a streamwise jet doubles when it is pulsated, whereas that of a compound angled jet increases by around 50%. It may be conjectured from the measurements shown in this study that streamwise oriented jets suffer most of their entropy losses at the hole exit due to separation, whereas in compound angled jets, downstream thermal mixing between the jet and the freestream is the dominant mechanism.

Copyright © 2009 by American Institute of Physics
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Figures

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Figure 1

Schematic of the test section for measurement with the FENT probe

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Figure 2

CIC plane traversing system for probe access shown in different configurations allowing for flexible spatial access

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Figure 3

Photograph of the tip of the fast entropy probe (FENT). The diameter of the head is 1.8 mm.

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Figure 4

Definition of the coordinate system and geometrical parameters

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Figure 5

Blowing ratio and pressure variation measured in the plenum with respect to time for BR=2, DR=1.3, and pulsation of 400 Hz, fr=0.025

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Figure 6

Time-averaged total pressure loss coefficient, CP,t, at X/D=6 for (a) β=0 deg, fr=0; (b) β=60 deg, fr=0; (c) β=0 deg, fr=0.025; and (d) β=60 deg, fr=0.025

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Figure 7

Time-averaged nondimensionalized temperature, θ=(T−Th)/(Tc−Th), at X/D=6 for (a) β=0 deg, fr=0 and (b) β=0 deg, fr=0.025. Time-averaged contours of the entropy function, e−Δs/R, shown for (c) β=0 deg, fr=0 deg and (d) β=0 deg, fr=0.025.

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Figure 8

Contours of the entropy function, e−Δs/R, of a pulsating jet at BR=2, DR=1.3, and β=0 deg shown at X/D=3,4,6, at the crest t/T=0.08, and at the trough t/T=0.64 during a pulsation

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Figure 9

Time-averaged nondimensionalized temperature, θ=(T−Th)/(Tc−Th), at X/D=6 for (a) β=60 deg, fr=0 and (b) β=60 deg, fr=0.025. Time-averaged contours of the entropy function, e−Δs/R, shown for (c) β=60 deg, fr=0 deg and (d) β=60 deg, fr=0.025.

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Figure 10

Contours of the entropy function, e−Δs/R, of a pulsating jet at BR=2, DR=1.3, and β=60 deg shown at X/D=3,4,6, at the crest t/T=0.08, and at the trough t/T=0.64 during a pulsation

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Figure 11

Evolution of mass flow weighted average of the total pressure loss coefficient CP,t (a) with distance from the hole center and (b) within a single pulsation of fr=0.025

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Figure 12

Evolution of mass flow weighted average of the entropy loss coefficient ζ with distance from the hole center with and without pulsations

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Figure 13

Evolution of mass flow weighted average of the entropy loss coefficient ζ at two distances and pulsation of fr=0.025

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Figure 14

Evolution of mass flow weighted average of the film cooling loss coefficient ξ with distance from the hole center with and without pulsations

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Figure 15

Evolution of mass flow weighted average of the film cooling loss coefficient ξ at two distances and pulsation of fr=0.025

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