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Research Papers

# Particle-Image Velocimetry Measurements of Film Cooling in an Adverse Pressure Gradient Flow

[+] Author and Article Information
Wilhelm Jessen

Institute of Aerodynamics, RWTH Aachen University, Wuellnerstraße 5a, 52062 Aachen, Germanyw.jessen@aia.rwth-aachen.de

Martin Konopka

Institute of Aerodynamics, RWTH Aachen University, Wuellnerstraße 5a, 52062 Aachen, Germanym.konopka@aia.rwth-aachen.de

Wolfgang Schroeder

Institute of Aerodynamics, RWTH Aachen University, Wuellnerstraße 5a, 52062 Aachen, Germanyoffice@aia.rwth-aachen.de

J. Turbomach 134(2), 021025 (Jul 07, 2011) (13 pages) doi:10.1115/1.4003175 History: Received August 27, 2010; Revised September 03, 2010; Published July 07, 2011; Online July 07, 2011

## Abstract

The turbulent flow field of a film cooling flow is investigated using the particle-image velocimetry technique. Cooling jets are injected from a multirow hole configuration into a turbulent boundary layer flow of a flat plate in the presence of a zero and an adverse pressure gradient. The investigations focus on full-coverage film cooling. Therefore, the film cooling configuration consists of three staggered rows of holes with a lateral spacing of $p/D=3$ and a streamwise row distance of $l/D=6$. The inclined cooling holes feature a fan-shaped exit geometry with lateral and streamwise expansions. Jets of air and $CO2$ are injected separately at different blowing ratios into a boundary layer to examine the effects of the density ratio between coolant and mainstream on the mixing behavior and consequently, the cooling efficiency. For the zero pressure gradient case, the measurement results indicate the different nature of the mixing process between the jets and the crossflow after the first, second, and third row. The mainstream velocity distributions evidence the growth of the boundary layer thickness at increasing row number. The interaction between the undisturbed boundary layer and first two rows leads to maximum values of turbulent kinetic energy. The presence of an adverse pressure gradient in the mainstream clearly intensifies the growth of the boundary layer thickness and increases the velocity fluctuations in the upper mixing zone. The measurements considering an increased density ratio show higher turbulence intensities in the shear zone between the jets and the main flow, leading to a more pronounced mixing in this area. The results of the experimental measurements are used to validate numerical findings from a large-eddy simulation. This comparison shows a very good agreement for mean velocity distributions and velocity fluctuations.

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## Figures

Figure 1

Fan-shaped cooling hole geometry

Figure 2

Sketch of the (a) zero and (b) adverse pressure configurations in the measurement section of the wind tunnel

Figure 3

Velocity distribution in the diverging channel

Figure 4

Schematic of the air/CO2 supply unit for the inclined injection

Figure 5

Sketch of the 3C-PIV setup showing the location of the jet exits and the coordinate system

Figure 6

Planes of 2C-PIV measurements for the multirow cooling configuration

Figure 7

Contours of the averaged mean velocity for air injection at MR=0.28 in the Z/D=1.5 symmetry plane

Figure 8

Profiles of streamwise velocity extracted at different downstream locations of each film cooling row for air injection at MR=0.28

Figure 9

Profiles of streamwise velocity fluctuations extracted at different downstream locations of each film cooling row for air injection at MR=0.28

Figure 10

3C-PIV measurement planes orthogonal to the main flow

Figure 11

Contours of the streamwise vorticity at ΔX/D=1 downstream of the trailing edge of each film cooling row for air injection at MR=0.28

Figure 12

Contours of the streamwise vorticity at ΔX/D=1 downstream of the trailing edge of each film cooling row for air injection at MR=0.48

Figure 13

Contours of the averaged mean velocity at an adverse pressure gradient (a) without injection and (b) for an air injection at MR=0.28 in the Z/D=1.5 symmetry plane. (c) The corresponding velocity profiles are displayed below.

Figure 14

Profiles of ((a) and (c)) streamwise velocity and ((b) and (d)) velocity fluctuations at ΔX/D=2 for air injection at MR=0.28 for the adverse and both zero pressure gradient configurations

Figure 15

Wall-normal velocity contours and velocity fields for air injection with a blowing ratio of MR=0.28 at X/D=3 at (a) a zero and (b) an adverse pressure gradient

Figure 16

Contours of the streamwise vorticity at X/D=3 downstream of the trailing edge of the second row for the (a) air and (b) CO2 injections at MR=0.28

Figure 17

Profiles of ((a) and (c)) streamwise velocity and ((b) and (d)) velocity fluctuations at X/D=3 for air and CO2 injections at MR=0.28 considering two pressure configurations

Figure 18

Contours of the film cooling effectiveness η and profiles of the adiabatic centerline effectiveness along the first and second row and the lateral average

Figure 19

((a)–(c)) Streamwise velocity and ((d)–(f)) velocity fluctuations profiles for air injection at MR=0.28 in the Z/D=0 symmetry plane at different locations of the second row; LES data: solid line, PIV data: ◻

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