Gas Turbines: Heat Transfer

The Effect of Particle Size and Film Cooling on Nozzle Guide Vane Deposition

[+] Author and Article Information
C. Bonilla, J. Webb, C. Clum, B. Casaday, E. Brewer, J. P. Bons

Department of Mechanical and Aerospace Engineering,  The Ohio State University, Columbus, OH 43235

J. Eng. Gas Turbines Power 134(10), 101901 (Aug 14, 2012) (8 pages) doi:10.1115/1.4007057 History: Received June 18, 2012; Revised June 21, 2012; Published August 14, 2012; Online August 14, 2012

An accelerated deposition test facility is used to study the effect of particle size and film cooling on deposit roughness, spatial distribution, and thickness. Tests were run at gas turbine representative inlet Mach numbers (0.08) and temperatures (1080 °C). Deposits were created from a subbituminous coal fly ash with mass median diameters from 4 to 16 micron (Stokes numbers ranging from 0.1 to 1.9). Two CFM56-5B nozzle guide vane doublets comprising three full passages and two half passages of flow were utilized as the test articles. Tests were run with three levels of film cooling. The addition of film cooling to the vanes was shown to decrease the deposit capture efficiency by as much as a factor of 3 and shift the primary location of deposit buildup to the leading edge, coincident with an increased region of positive cooling backflow margin. Video taken during the tests noted that film cooling holes with a negative backflow margin were primary areas of deposit formation, regardless of the film cooling percentage. The Stokes number was shown to have a marked effect on the vane capture efficiency, with the largest Stokes number ash (St = 1.9) approximately 3 times as likely to stick to the vane as the smallest Stokes number ash (St = 0.1). Posttest observations on the deposit thickness were made using a coordinate measurement machine. The deposit thickness was noted to be reduced with a decreasing Stokes number and an increased film cooling percentage. The deposit surface roughness falls with particle size but is only weakly dependent on the cooling level.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Schematic of the TuRFR showing the primary flow path, particulate, fuel, and film cooling insertion points

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Figure 2

Cutaway of the TuRFR measurement and viewing area

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Figure 3

Average particle size distribution for the JBPS coal fly ash

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Figure 4

CFM56 schematic showing cooling rows with a negative backflow margin for low and high FC

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Figure 5

Snapshots of deposit tests at various times during the testing period. Image (a) shows a photograph matching the video’s perspective. Image (b) shows the area recorded on the doublet.

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Figure 6

Image of the scanned vane for (a) no FC, St ≈ 1.9, (b) no FC, St ≈ 0.1, (c) high FC, St ≈ 1.1, (d) high FC, St ≈ 0.3

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Figure 7

Surface normal deposit thickness versus wetted distance for 2 Stokes numbers without film cooling

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Figure 8

Surface normal deposit thickness versus wetted distance for no and low film cooling for small and large Stokes values

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Figure 9

Surface normal deposit thickness plot for no, low, and high FC at Stokes values of 1.9 and 1.1. Green vertical lines indicate the location of coolant rows (also see Fig. 4).

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Figure 10

Particulate capture efficiencies (no FC) compared to data from Crosby [7] and Barker [4]

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Figure 11

Cooled vane capture efficiency versus coolant mass flow to the wetted surface area ratio




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