Research Papers

Effect of Blowing Ratio on Early Stage Deposition of Syngas Ash on a Film-Cooled Vane Leading Edge Using Large Eddy Simulations

[+] Author and Article Information
Danesh K. Tafti

e-mail: dtafti@vt.eduHigh Performance Computational Fluid-Thermal
Sciences and Engineering Laboratory,
Mechanical Engineering Department,
Virginia Polytechnic Institute and
State University,
Blacksburg VA 24061

The notation (aj)i is used to denote the ith component of vector aj, (aj)i=ξj/xi.

For an estimate of the lowest radiative Stokes number (Tp=T).

The values of A are corrected values pointed out by Vargas [26].

The computations assume a coolant to mainstream density ratio of 1 (see Table 3).

1Presently at: ATMS, GE Global Research, 122, EPIP, Whitefield Road, Bangalore 560 066, Karnataka, India.

2Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received October 29, 2010; final manuscript received August 5, 2011; published online September 13, 2013. Assoc. Editor: Karen A. Thole.

J. Turbomach 135(6), 061005 (Sep 13, 2013) (12 pages) Paper No: TURBO-10-1205; doi: 10.1115/1.4025153 History: Received October 29, 2010; Revised August 05, 2011

A numerical study is performed to investigate the deposition of Syngas ash in the leading edge region of a turbine vane. The leading edge of the vane is modeled as a symmetric semicylinder with a flat afterbody. Three rows of coolant holes located at stagnation and at ±21.3 deg from stagnation are simulated at blowing ratios of 0.5, 1.0, 1.5, and 2.0. Large eddy simulation (LES) is used to model the flow field of the coolant jet-mainstream interaction and Syngas ash particles are modeled using a discrete particle method. The capture efficiency for eight different ash compositions of particle sizes 5 and 10 microns are investigated. Under the conditions of the current simulations, both ash particles have Stokes numbers less than unity and hence are strongly affected by the flow and thermal field generated by the coolant interaction with the mainstream. Because of this, the coolant jets at stagnation are quite successful in pushing the particles away from the surface and minimizing deposition in the stagnation region. Among all of the ash samples, the ND ash sample shows the highest capture efficiency due to its low softening temperature. For the 5 micron particles, when the blowing ratio increases from 1.5 to 2.0, the percentage of the capture efficiency increases as more numbers of particles are transported to the surface by strong mainstream entrainment by the coolant jets. The deposition results are also estimated using the discrete random walk (DRW) model and are compared to that obtained from the LES calculations. For both particle sizes, the DRW model under-predicts the capture efficiency when compared to the LES calculations and the difference increases with the increasing blowing ratio and decreases with increasing particle size.

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Fig. 1

Transition to the modified deposition model using the critical viscosity approach (Ps is the sticking probability and Ts is the ash softening temperature [15])

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Fig. 2

Temperature-viscosity variation for various ash samples

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Fig. 3

Leading edge vane model and near field streamwise planes used in presenting the results

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Fig. 4

Computational domain in the side view (X-Y plane)

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Fig. 5

Structure of coherent vorticity: (a) BR = 0.5 (iso-surface value = 30), and (b) BR = 2.0 (iso-surface value = 75)

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Fig. 6

Effectiveness on the vane surface: (a) BR = 0.5, (b) BR = 1.0, (c) BR = 1.5, and (d) BR = 2.0

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Fig. 7

Lateral span averaged effectiveness on the vane surface

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Fig. 8

Impact efficiency as a function of the blowing ratio

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Fig. 9

Capture efficiency as a function of the blowing ratio for the ND ash sample (see Table 2)

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Fig. 10

Percentage capture efficiency of 5 μm ash particles on the leading edge vane surface for the ND ash sample (the direction of the coolant is from right to left)

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Fig. 11

Percentage capture efficiency of 10 μm ash particles on the leading edge vane surface for the ND ash sample (the direction of the coolant is from right to left)

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Fig. 12

Capture efficiency for all ash samples having a particle size of 5 μm at different blowing ratios (the dotted horizontal line indicates the deposition at Tsoft = 1500 K, independent of ash composition)

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Fig. 13

Capture efficiency for all ash samples having a particle size of 10 μm at different blowing ratios (the dotted horizontal line indicates the deposition at Tsoft = 1500 K, independent of ash composition)




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