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Research Papers

An Experimental Study of Mist/Air Film Cooling On a Flat Plate With Application to Gas Turbine Airfoils—Part II: Two-Phase Flow Measurements and Droplet Dynamics

[+] Author and Article Information
Lei Zhao

e-mail: leizhao.me@gmail.com;
lei.zhao@dupont.com

Ting Wang

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

1Currently at E. I. du Pont de Nemours and Company, Wilmington, DE 19805.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 15, 2013; final manuscript received August 30, 2013; published online January 2, 2014. Editor: Ronald Bunker.

J. Turbomach 136(7), 071007 (Jan 02, 2014) (9 pages) Paper No: TURBO-13-1190; doi: 10.1115/1.4025738 History: Received August 15, 2013; Revised August 30, 2013

A phase Doppler particle analyzer (PDPA) system is employed to measure the two-phase mist flow behavior including flow velocity field, droplet size distribution, droplet dynamics, and turbulence characteristics. Based on the droplet measurements made through PDPA, a projected profile describing how the air-mist coolant jet flow spreads and eventually blends into the hot main flow is proposed. This proposed profile is found to be well supported by the measurement results of the turbulent Reynolds stresses. The coolant film envelope is identified with shear layers characterized by higher magnitudes of turbulent Reynolds stresses. In addition, the separation between the mist droplet layer and the coolant air film is identified through the droplet measurements—large droplets penetrate through the air coolant film layer and travel further into the main flow. With the proposed air-mist film profile, the heat transfer results on the wall presented in Part I are re-examined and more in-depth physics is revealed. It is found that the location of the optimum cooling effectiveness coincides with the point where the air-mist coolant stream starts to bend back towards the surface. Thus, the data suggests that the “bending back” film pattern is critical in keeping the mist droplets close to the surface, which improves the cooling effectiveness for mist cooling.

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Figures

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Fig. 1

Calibration of the PDPA measurement with the monosized polymer latex particles

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Fig. 2

Contour of the cooling effectiveness for (a) case 1, M = 0.6, air-only film, and (b) case 2, M = 0.6, mist/air film (identical to Fig. 2 in Part I)

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Fig. 3

Comparison of the present adiabatic cooling effectiveness (left coordinate) and net enhancement (right coordinate) with the experimental data from Goldstein et al. and Rhee et al. for (a) M = 0.6, centerline data, and (b) M = 0.6, spanwise averaged data (identical to Fig. 2 in Part I)

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Fig. 4

Droplet size distribution of various Y locations at X/D = 1, M = 0.66

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Fig. 5

Droplet size distribution of various Y locations at X/D = 6, M = 0.66

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Fig. 6

Droplet size distribution of various Y locations at X/D = 13, M = 0.66

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Fig. 7

Droplet size distribution of various Y locations at X/D = 28, M = 0.66

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Fig. 8

Case 2 (M = 0.6) particle size distribution (on the left Y coordinate) and particle data rate distribution (on the right Y coordinate) as a function of the Y locations at (a) X/D = 1, (b) X/D = 6, (c) X/D = 13, and (d) X/D = 28

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Fig. 9

Case 2 (M = 0.6) droplet size distribution (plotted on the Y-coordinate on the left) and the Reynolds stress distribution (plotted on the Y-coordinate on the right) as a function of the Y-locations at (a) X/D = 1, (b) X/D = 6, (c) X/D = 13, and (d) X/D = 28

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Fig. 10

Particle size distribution (plotted on the Y-coordinate on the left) and the droplets' mean velocity (plotted on the Y-coordinate on the right) as a function of the Y locations at (a) X/D = 1, (b) X/D = 6, (c) X/D = 13, and (d) X/D = 28

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Fig. 11

Droplet size distribution on the centerline for case 2, M = 0.6

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Fig. 12

Illustration for the droplet distribution profile for a low blowing ratio (M = 0.6) mist film cooling

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Fig. 13

The midplane shape of the mist/air coolant film layer for the M = 0.6 case at the hole centerline with the net enhancement of cooling effectiveness plotted on the right Y-axis

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