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RESEARCH PAPERS: Turbine Blade Cooling

Increasing Adiabatic Film-Cooling Effectiveness by Using an Upstream Ramp

[+] Author and Article Information
Sangkwon Na

Department of Aerospace Engineering,  Iowa State University, Ames, IA 50011-2271

Tom I-P. Shih

Department of Aerospace Engineering,  Iowa State University, Ames, IA 50011-2271tomshih@iastate.edu

J. Heat Transfer 129(4), 464-471 (Dec 14, 2006) (8 pages) doi:10.1115/1.2709965 History: Received March 04, 2006; Revised December 14, 2006

A new design concept is presented to increase the adiabatic effectiveness of film cooling from a row of film-cooling holes. Instead of shaping the geometry of each hole; placing tabs, struts, or vortex generators in each hole; or creating a trench about a row of holes, this study proposes a geometry modification upstream of the holes to modify the approaching boundary-layer flow and its interaction with the film-cooling jets. Computations, based on the ensemble-averaged Navier–Stokes equations closed by the realizable kε turbulence model, were used to examine the usefulness of making the surface just upstream of a row of film-cooling holes into a ramp with a backward-facing step. The effects of the following parameters were investigated: angle of the ramp (8.5deg, 10deg, 14deg), distance between the backward-facing step and the row of film-cooling holes (0.5D,D), blowing ratio (0.36, 0.49, 0.56, 0.98), and “sharpness” of the ramp at the corners. Results obtained show that an upstream ramp with a backward-facing step can greatly increase surface adiabatic effectiveness. The laterally averaged adiabatic effectiveness with a ramp can be two or more times higher than without the ramp by increasing upstream and lateral spreading of the coolant.

Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the upstream ramp studied

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Figure 2

Schematic of the film-cooling configuration studied (not drawn to scale and ramp not included)

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Figure 3

Schematic of film cooling of a flat plate from a row of inclined circular holes with an upstream ramp

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Figure 4

Schematic of an upstream ramp with rounded corners

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Figure 5

Grid-independence study: centerline adiabatic effectiveness for three grids at M=0.5

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Figure 6

Grid used: (a) no ramp; (b) with ramp; and (c) grid around film-cooling hole

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Figure 7

y+ values at one cell above the surface of the flat plat with ramp

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Figure 8

Validation study: CFD predictions and comparison with experimental data of Kohli and Bogard (L∕D=2.8 to match experiment): (a) laterally averaged; and (b) centerline

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Figure 9

Static gage pressure (Pa) on the flat plate about the film-cooling hole (α=8.5deg, β=1.0D, M=0.49): (a) no ramp; and (b) with ramp

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Figure 10

Pressure coefficient on the plate along center line (α=14.0deg, β=0.5D, M=0.49): (a) with and without ramp; (b) with sharp and rounded corners; and (c) with ramp in channels of different heights

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Figure 11

Streamlines colored by temperature with darker gray being higher and lighter gray being lower (α=8.5deg, β=0.5D, M=0.49)

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Figure 12

Velocity vectors and streamlines in an X‐Z plane that passes through the center of the film-cooling hole (α=8.5deg, β=0.5D, M=0.49). Lighter gray denotes higher speed region. Darker gray denotes lower speed region with separation.

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Figure 13

Normalized temperature (T∞−T)∕(T∞−Tc) at Y‐Z plane located at X∕D=3 (α=14deg, β=0.5D, M=0.49): (left half) no ramp; and (right half) with ramp

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Figure 14

Adiabatic effectiveness on the flat plate about the film-cooling hole (α=8.5deg, β=1D, M=0.49): (a) no ramp; and (b) with ramp

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Figure 15

Adiabatic effectiveness with and without ramp: (a) centerline; and (b) laterally averaged

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Figure 16

Adiabatic effectiveness as a function of α (β=D and M=0.49): (top half) α=8.5deg; and (bottom half) α=14deg

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Figure 17

Adiabatic effectiveness as a function of β (α=14deg and M=0.49): (top half) β=1.0D; and (bottom half) β=0.5D

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Figure 18

Adiabatic effectiveness as a function of blowing ratio (α=8.5deg, β=D): (a) centerline adiabatic effectiveness; and (b) laterally averaged adiabatic effectiveness

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Figure 19

Effects of rounding the sharp corners of the upstream ramp (α=14.0deg, β=0.5D): (a) centerline adiabatic effectiveness; and (b) laterally averaged adiabatic effectiveness

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Figure 20

Normalized surface heat flux (M=0.49, α=14deg, and β=0.5D): (a) no ramp; and (b) with ramp

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Figure 21

Normalized surface heat flux along the centerline with and without ramp (α=14deg, β=0.5D, M=0.49)

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