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Gas Turbines: Heat Transfer

Influence of Film Cooling Unsteadiness on Turbine Blade Leading Edge Heat Flux

[+] Author and Article Information
James L. Rutledge

Paul I. King

 Air Force Institute of Technology, Wright-Patterson Air Force Base, OH 45433

Richard B. Rivir

 Air Force Research Laboratory, Wright-Patterson Air Force Base, OH 45433

J. Eng. Gas Turbines Power 134(7), 071901 (May 23, 2012) (10 pages) doi:10.1115/1.4005978 History: Received August 24, 2011; Revised October 24, 2011; Published May 23, 2012; Online May 23, 2012

Film cooling in the hot gas path of a gas turbine engine can protect components from the high temperature main flow, but it generally increases the heat transfer coefficient h partially offsetting the benefits in reduced adiabatic wall temperature. We are thus interested in adiabatic effectiveness η and h which are combined in a formulation called net heat flux reduction (NHFR). Unsteadiness in coolant flow may arise due to inherent unsteadiness in the external flow or be intentionally introduced for flow control. In previous work it has been suggested that pulsed cooling flow may, in fact, offer benefits over steady blowing in either improving NHFR or reducing the mass flow requirements for matched NHFR. In this paper we examine this hypothesis for a range of steady and pulsed blowing conditions. We use a new experimental technique to analyze unsteady film cooling on a semicircular cylinder simulating the leading edge of a turbine blade. The average NHFR with pulsed and steady film cooling is measured and compared for a single coolant hole located 21.5° downstream from the leading edge stagnation line, angled 20° to the surface and 90° to the streamwise direction. We show that for moderate blowing ratios at blade passing frequencies, steady film flow yields better NHFR. At higher coolant flow rates beyond the optimum steady blowing ratio, however, pulsed film cooling can be advantageous. We present and demonstrate a prediction technique for unsteady blowing at frequencies similar to the blade passing frequency that only requires the knowledge of steady flow behavior. With this important result, it is possible to predict when pulsing would be beneficial or detrimental.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Leading edge model

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Figure 2

Right handed coordinate system (y into page)

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Figure 3

Schematic of coolant feed line

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Figure 4

M(t) for M¯ = 0.50, 20 Hz, DC = 50%, PVC, ReD  = 60 k; M is doubled for ReD  = 30 k

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Figure 5

M(t) for M¯ = 1.0, 40 Hz, DC = 50%, PVC, ReD  = 60 k; M is doubled for ReD  = 30 k

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Figure 6

M(t) for M¯ = 0.50, 20 Hz, DC = 50%, CVC, ReD  = 60 k; M is doubled for ReD  = 30 k

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Figure 7

Adiabatic effectiveness-steady film cooling, M = 0.5, low Tu, ReD  = 60 k

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Figure 8

Adiabatic effectiveness-steady film cooling, M = 0.5, high Tu, ReD  = 60 k

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Figure 9

Adiabatic effectiveness-steady film cooling, M = 0.5, low Tu, ReD  = 30 k

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Figure 10

Frössling number with no film cooling

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Figure 11

Fr/Fr0 contours for steady film cooling, M = 0.5, low Tu, ReD  = 60 k

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Figure 12

Fr/Fr0 contours for steady film cooling, M = 0.5, high Tu, ReD  = 60 k

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Figure 13

Fr/Fr0 contours for steady film cooling, M = 0.5, low Tu, ReD  = 30 k

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Figure 14

Net heat flux reduction, Δqr, steady film cooling, M = 0.5, low Tu, ReD  = 60 k

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Figure 15

Net heat flux reduction, Δqr, steady film cooling, M = 0.5, high Tu, ReD  = 60 k

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Figure 16

Net heat flux reduction, Δqr, steady film cooling, M = 0.5, low Tu, ReD  = 30 k

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Figure 17

Area averaged Δqr for steady film cooling

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Figure 18

Δqr¯ contours for M¯= 0.25, low Tu, ReD  = 60 k, F = 0.148, DC =  50%, PVC

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Figure 19

Δqr¯ contours for M¯= 0.25, low Tu, ReD  = 60 k, F = 0.148, DC = 50%, CVC

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Figure 20

Δqr¯ contours for M = 2.0, low Tu, ReD  = 60 k, steady film cooling

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Figure 21

Δqr¯ contours for M¯ = 2.0, low Tu, ReD  = 60 k, F = 0.148, DC = 50%, PVC

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Figure 22

Net heat flux reduction due to pulsing as a function of M¯; low Tu,ReD  = 60 k

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Figure 23

Net heat flux reduction due to pulsing as a function of M¯, high Tu, ReD  = 60 k

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Figure 24

Net heat flux reduction due to pulsing as a function of M¯, low Tu, ReD  = 30 k

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Figure 25

Net heat flux reduction due to pulsing as a function of M¯, high Tu, ReD  = 30 k

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Figure 26

Net heat flux reduction due to pulsing as a function of M¯; low Tu.ReD  = 60 k; low frequency prediction versus actual results.

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Figure 27

Area averaged Δqr,pulsed¯, sinusoidal M(t). Max Δqr,pulsed¯ = 6.6% at M¯ = 1.88, amplitude = 1.62.

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Figure 28

Area averaged Δqr,pulsed¯, square wave M(t). Max Δqr,pulsed¯ = 10.9% at M¯ = 1.88, amplitude = 1.62.

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Figure 29

Area averaged Δqr,pulsed¯, triangle wave M(t). Linear ramp up and down. Max Δqr,pulsed¯ = 5.0% at M¯ = 1.98, amplitude = 1.52.

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