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Research Papers

Experimental Simulation of Contaminant Deposition on a Film Cooled Turbine Airfoil Leading Edge

[+] Author and Article Information
Jason E. Albert, David G. Bogard

Department of Mechanical Engineering,  The University of Texas at Austin, Austin, TX 78712

J. Turbomach 134(5), 051014 (May 11, 2012) (10 pages) doi:10.1115/1.4003964 History: Received December 28, 2010; Revised March 07, 2011; Published May 10, 2012; Online May 11, 2012

A significant challenge of utilizing coal-derived synthetic fuels for gas turbine engines is mitigating the adverse effects of fuel-born contaminant deposits on film cooled turbine surfaces. A new experimental technique has been developed that simulates the key physical, but not the chemical, aspects of coal ash deposition on film cooled turbine airfoil leading edges in order to better understand the interaction between film cooling and deposition and to produce improved film cooling designs. In this large-scale wind tunnel facility, the depositing contaminants were modeled with atomized molten wax droplets sized to match the Stokes numbers of coal ash particles in the engine conditions. The sticking mechanism of the molten contaminants to the turbine surfaces was modeled by ensuring the wax droplets remained somewhat molten when they arrived at the cooled model surface. The airfoil model and wax deposits had thermal conductivities such that they matched the Biot numbers of clean and fouled turbine airfoils at engine conditions. The behavior of the deposit growth was controlled by adjusting the mainstream, coolant, and wax solidification temperatures. Simulated deposits were created for a range of test durations, film cooling blowing ratios, and controlling temperatures. Inspection of the resulting deposits revealed aspects of the flow field that augment and suppress deposition. Deposit thickness was found to increase in time until an equilibrium thickness was attained. Blowing ratio and the difference between mainstream and wax solidification temperatures strongly affected characteristics of the deposits. Model surface temperatures greatly reduced under the deposits as they developed.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of wind tunnel facility

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Figure 2

Schematic of leading edge model

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Figure 3

Schematic of wax spray device

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Figure 4

Photograph of test section with wax spray device in place (flow direction left to right)

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Figure 5

Analytical results for travel distance to complete wax droplet solidification in wind tunnel mainstream, U∞  = 15 m/s, T∞  = 297 K

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Figure 6

SEM image of sprayed wax droplets from the current facility, showing the desired size range of 8–80 μm

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Figure 7

Photo of non-film-cooled model deposit for Case AA (τspray  = 20 min, ΔTsolid  = 19 K)

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Figure 8

Photo of film-cooled model deposit for Case A (M = 2.0, τspray  = 20 min, ΔTsolid  = 18 K)

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Figure 9

Same photo as Fig. 8, with regions of high η outlined in red and high hf /ho outlined in yellow

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Figure 10

Deposit thickness variation along stagnation line, between cooling holes for Case A (see also Fig. 8)

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Figure 11

Photo of film-cooled model deposit for Case C (M = 2.0, τspray  = 10 min, ΔTsolid  = 18 K)

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Figure 12

Final deposit thicknesses for several experiments (Cases A, B, and C)

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Figure 13

Change in surface temperature midway between stagnation row holes (in terms of φ) during experiments with varying spray durations

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Figure 14

Photo of model deposit for Case D (M = 1.0, τspray  = 15 min, ΔTsolid  = 18 K)

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Figure 15

Photo of model deposit for Case E (M = 2.0, τspray  = 15 min, ΔTsolid  = 2 K, Tsolid,wax  = 315 K)

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Figure 16

Photo of model deposit for Case G (M = 2.0, τspray  = 15 min, ΔTsolid  = 10 K, Tsolid,wax  = 304 K)

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Figure 17

Photo of model deposit for Case F (M = 2.0, τspray  = 15 min, ΔTsolid  = −9 K, Tsolid,wax  = 304 K)

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