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Research Papers: Jets, Wakes, and Impingement Cooling

# Calibration of a Computational Model to Predict Mist/Steam Impinging Jets Cooling With an Application to Gas Turbine Blades

[+] Author and Article Information
Ting Wang

Energy Conversion and Conservation Center, University of New Orleans, New Orleans, LA 70148-2220twang@uno.edu

T. S. Dhanasekaran

Energy Conversion and Conservation Center, University of New Orleans, New Orleans, LA 70148-2220tdhanase@uno.edu

J. Heat Transfer 132(12), 122201 (Sep 17, 2010) (11 pages) doi:10.1115/1.4002394 History: Received April 13, 2009; Revised July 07, 2010; Published September 17, 2010; Online September 17, 2010

## Abstract

In heavy-frame advanced turbine systems, steam is used as a coolant for turbine blade cooling. The concept of injecting mist into the impinging jets of steam was experimentally proved as an effective way of significantly enhancing the cooling effectiveness in the laboratory under low pressure and temperature conditions. However, whether or not mist/steam cooling is applicable under actual gas turbine operating conditions is still subject to further verification. Recognizing the difficulties of conducting experiments in an actual high-pressure, high-temperature working gas turbine, a simulation using a computational fluid dynamic (CFD) model calibrated with laboratory data would be an opted approach. To this end, the present study conducts a CFD model calibration against the database of two experimental cases including a slot impinging jet and three rows of staggered impinging jets. The calibrated CFD model was then used to predict the mist cooling enhancement at the elevated gas turbine working condition. Using the experimental results, the CFD model has been tuned by employing different turbulence models, computational cells, and wall $y+$ values. In addition, the effects of different forces (e.g., drag, thermophoretic, Brownian, and Saffman’s lift force) are also studied. None of the models is a good predictor for all the flow regions from near the stagnation region to far-field downstream of the jets. Overall speaking, both standard $k-ε$ and Reynolds stress model (RSM) turbulence models perform better than other models. The RSM model has produced the closest results to the experimental data due to its capability of modeling the nonisotropic turbulence shear stresses in the 3D impinging jet fields. The simulated results show that the calibrated CFD model can predict the heat transfer coefficient of steam-only case within 2–5% deviations from the experimental results for all the cases. When mist is employed, the prediction of wall temperatures is within 5% for a slot jet and within 10% for three-row jets. The predicted results with 1.5% mist at the gas turbine working condition show the mist cooling enhancement of 20%, whereas in the laboratory condition, the enhancement is predicted as 80%. Increasing mist ratio to 5% increased the cooling enhancement to about 100% at the gas turbine working condition.

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## Figures

Figure 1

(a) Experimental setup (7) and computational geometry details of (b) slot jet and (c) three-row jets

Figure 2

Computational domain: (a) slot jet and (b) multiple-row of staggered jets

Figure 3

Grid sensitivity study: (a) slot jet and (b) three-row jets

Figure 4

Wall temperature distribution of a slot jet model

Figure 5

Velocity vector plot: (a) standard k-ε, (b) RNG, (c) RSM, (d) k-ω, and (e) SST

Figure 6

Effect of computational domain on slot impinging jet cooling (steam-only)

Figure 7

Effect of (a) main and secondary forces on the droplet model and (b) stochastic tracking time scale constant (TC) on the slot jet model

Figure 8

Heat transfer prediction of the slot impingement jet: (a) wall temperature, (b) heat transfer coefficient, and (c) cooling enhancement

Figure 9

Droplet concentration distributions across the channel height at various x-locations of slot jet cases: (a) 1% mist and (b) 2% mist

Figure 10

Effect of y+ values of 12 and 20 with standard wall function on centerline temperature distribution along the first row jet for three-row impinging jets model (steam-only)

Figure 11

(a) Experimental droplet size distribution and heat transfer results of three-row jets: (b) wall temperature and (c) heat transfer coefficient

Figure 12

Heat transfer results of three-row jets: (a) lower and (b) elevated operating conditions

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