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Research Papers

# Effect of Hole Spacing on Deposition of Fine Coal Flyash Near Film Cooling Holes

[+] Author and Article Information
Weiguo Ai1

Department of Chemical Engineering, Brigham Young University, Provo, UT 84602aiweiguo@byu.net

Nathan Murray, Thomas H. Fletcher

Department of Chemical Engineering, Brigham Young University, Provo, UT 84602

Spencer Harding

Department of Mechanical Engineering, Brigham Young University, Provo, UT 84602

Jeffrey P. Bons

Department of Mechanical Engineering, Ohio State University, Columbus, OH 43210

1

Corresponding author.

J. Turbomach 134(4), 041021 (Jul 25, 2011) (9 pages) doi:10.1115/1.4003717 History: Received October 21, 2010; Revised December 01, 2010; Published July 25, 2011; Online July 25, 2011

## Abstract

Particulate deposition experiments were performed in a turbine accelerated deposition facility to examine the nature of flyash deposits near film cooling holes. Deposition on both bare metal and thermal barrier coating (TBC) coupons was studied, with hole spacing (s/d) of 2.25, 3.375, and 4.5. Sub-bituminous coal ash particles (mass mean diameter of $13 μm$) were accelerated to a combustor exit flow Mach number of 0.25 and heated to $1183°C$ before impinging on a target coupon. The particle loading in the 1 h tests was 310 ppmw. Blowing ratios were varied in these experiments from 0 to 4.0 with the density ratio varied approximately from 1.5 to 2.1. Particle surface temperature maps were measured using two-color pyrometry based on the red/gree/blue (RGB) signals from a camera. For similar hole spacing and blowing ratio, the capture efficiency measured for the TBC surface was much higher than for the bare metal coupon due to the increase of surface temperature. Deposits on the TBC coupon were observed to be more tenacious (i.e., hard to remove) than deposits on bare metal coupons. The capture efficiency was shown to be a function of both the hole spacing and the blowing ratio (and hence surface temperature). Temperature seemed to be the dominant factor affecting deposition propensity. The average spanwise temperature downstream of the holes for close hole spacing was only slightly lower than for the large hole spacing. Roughness parameters Ra and Rt decreased monotonically with increased blowing ratio for both hole spacing analyzed. The roughness for $s/d=3.375$ was lower than that for $s/d=4.5$, especially at high blowing ratio. It is thought that these data will prove useful for designers of turbines using synfuels.

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## Figures

Figure 8

Capture efficiency measured for M3 and TBC coupons with three holes and s/d=4.5 as a function of blowing ratio. Error bars represent duplicate experiments.

Figure 9

Spanwise distribution of temperature at y/d=2.0 for the metal coupon and TBC coupon with three holes, s/d=4.5, and M=2.0

Figure 10

Deposit thickness variation map at M=4.0 for s/d=4.5: (a) TBC coupon and (b) bare metal coupon (M3) (three holes blowing)

Figure 11

Variation of deposit patterns on the surface of coupon with three holes, s/d=3.375d, and M from M=0 to M=2.0

Figure 12

Capture efficiency at various blowing ratios for bare metal coupons with three holes, s/d=3.375 and 4.5. Error bars represent duplicate experiments.

Figure 13

Roughness statistics of deposit on bare metal coupon with three holes and varying hole spacing in the downstream region

Figure 14

Surface temperature maps of metal coupons during deposition for blowing ratios and hole spacing (a) M=0.5, s/d=3.375, (b) M=1.0, s/d=3.375, (c) M=2.0, s/d=3.375, (d) M=0.5, s/d=4.5, (e) M=1.0, s/d=4.5, (f) M=2.0, s/d=4.5. Color bar indicates surface temperature in Kelvin. Flow is upward in these figures (‘‘three holes blowing’’).

Figure 6

Variation of deposit patterns on bare metal coupon with three holes, s/d=4.5, and blowing ratios from M=0, 0.5, 1.0, 2.0 and 4.0

Figure 7

Spanwise distribution of temperature for the metal coupon three holes, s/d=4.5 at y/d=2.0, M=0.5, 1.0, and 2.0, respectively

Figure 15

Spanwise temperature distribution at y/d=2.0 downstream of the cooling holes for M=1 and with s/d=3.375 (cross-hatched holes) and 4.5 (solid holes), respectively (three holes blowing)

Figure 16

Streamwise surface temperature distributions along the centerline downstream of the middle hole at different blowing ratios: (a) s/d=3.375 and (b) s/d=4.5d (three holes blowing)

Figure 1

Schematic of the BYU accelerated turbine deposition facility

Figure 2

Coupon geometry: (a) TBC sample coupon with s/d=2.25, (b) bare metal coupon with s/d=4.5, and (c) bare metal coupon with s/d=3.375

Figure 3

Ash particle size distribution. Mass mean particle size is 13.4 μm.

Figure 4

Variation of deposit patterns on the TBC coupon with (a) s/d=2.25 (five holes), (b) s/d=4.5 (three holes), and (c) s/d=2.25 (three holes) at M=2.0

Figure 5

Spanwise distribution of surface temperature for TBC coupon at y/d=2.5 and M=2.0 for s/d=2.25(five holes), s/d=4.5(three holes), and s/d=2.25(middle three holes)

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