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Research Papers: Evaporation, Boiling, and Condensation

Simulation of Mist Film Cooling on Rotating Gas Turbine Blades

[+] Author and Article Information
T. S. Dhanasekaran1

Energy Conversion and Conservation Center,  University of New Orleans, New Orleans, LA 70148-2220tsdhana@gmail.com

Ting Wang

Energy Conversion and Conservation Center,  University of New Orleans, New Orleans, LA 70148-2220tsdhana@gmail.com

1

Corresponding author.

J. Heat Transfer 134(1), 011501 (Oct 28, 2011) (11 pages) doi:10.1115/1.4004480 History: Received March 04, 2010; Revised June 19, 2011; Accepted June 23, 2011; Published October 28, 2011; Online October 28, 2011

Film cooling techniques have been successfully applied to gas turbine blades to protect them from the hot flue gas. However, a continuous demand of increasing the turbine inlet temperature to raise the efficiency of the turbine requires continuous improvement in film cooling effectiveness. The concept of injecting mist (tiny water droplets) into the cooling fluid has been proven under laboratory conditions to significantly augment adiabatic cooling effectiveness by up to 50%–800% in convective heat transfer and impingement cooling. The similar concept of injecting mist into air film cooling has not been proven in the laboratory, but computational simulations have been performed on stationary turbine blades. As a continuation of previous research, this paper extends the mist film cooling scheme to the rotating turbine blade. For the convenience of understanding the effect of rotation, the simulation is first conducted with a single pair of cooling holes located near the leading edge at either side of the blade. Then, a row of multiple-hole film cooling jets is put in place under both stationary and rotating conditions. Both the laboratory (baseline) and elevated gas turbine conditions are simulated and compared. Elevated conditions refer to a high temperature and pressure closer to actual gas turbine working conditions. The effects of various parameters including mist concentration, water droplet diameter, droplet wall boundary condition, blowing ratio, and rotational speed are investigated. The results showed that the effect of rotation on droplets under laboratory conditions is minimal. The computational fluid dynamics (CFD) model employed is the discrete phase model (DPM) including both wall film and droplet reflect conditions. The results showed that the droplet-wall interaction is stronger on the pressure side than on the suction side, resulting in a higher mist cooling enhancement on the pressure side. The average rates of mist cooling enhancement of about 15% and 35% were achieved under laboratory and elevated conditions, respectively. This translates to a significant blade surface temperature reduction of 100–125 K with 10% mist injection at elevated conditions.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Geometry and boundary conditions of the single stage turbine model and (b) film cooling hole orientation and geometry of a single row configuration

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Figure 2

Elements on the rotor and stator. The film hole is located at the midspan of turbine blade (z = 0.635 m)

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Figure 3

Qualification of mist cooling computational model by comparing with the experimental results of a mist impinging jet conducted by Li [25]

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Figure 4

Heat transfer results of baseline case: Re = 1.6 × 105 , 5 μm, 2% mist, 289 RPM, baseline condition, cooling hole location is at z = 0.365

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Figure 5

(a) Temperature distribution and (b) adiabatic film effectiveness on the pressure surface of a single film hole: (i) air only and (ii) mist/air (Re = 1.6 × 105 , 5 μm, 2% mist, 289 RPM, baseline condition)

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Figure 6

Air only film cooling pathlines and droplet traces: Re = 1.6 × 105 , 5 μm, 2% mist, 289 RPM, baseline condition (viewed from hub to tip)

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Figure 7

Effect of discrete phase model wall boundary conditions: reflect versus wall-film model (Re = 1.6 × 105 , 5 μm, 2% mist, 289 RPM, baseline condition)

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Figure 8

Effect of rotational speed on mist/air film cooling (Re = 1.6 × 105 , 5 μm, 2% mist, baseline condition)

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Figure 9

Static pressure distribution on the blade surface showing effect of rotation (Re = 1.6 × 105 , 5 μm, 2% mist, baseline condition). The color on the surface represents static pressure relative to the operating pressure at 101.325 Pascal. The velocity magnitude is represented by both color and vector length

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Figure 10

Effect of mist concentration (Re = 1.6 × 105 , 5 μm, 289 RPM, baseline condition)

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Figure 11

Effect of blowing ratio on air-only and mist/air film cooling (Re = 1.6 × 105 , 5 μm, 2% mist, 289 RPM, baseline condition)

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Figure 12

Effect of droplet diameter: Re = 1.6 × 105 , 5 μm, 2% mist, 289 RPM, baseline condition

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Figure 13

Effect of mist cooling on pressure and suction sides: Re = 1.6 × 105 , 5 μm, 2% mist, 289 RPM, baseline condition (film hole located at z = 0.365)

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Figure 14

Distribution of film cooling effectiveness: Re = 1.6 × 105 , 5 μm, 2%mist, 289 RPM, baseline condition

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Figure 15

Adiabatic film cooling effectiveness of mist cooling for multiple-hole single row configuration: Re = 1.6 × 105 , 5 μm, 2% mist, 289 RPM, baseline condition

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Figure 16

Mist film cooling performance at elevated condition: Re = 38 × 105 , 5 μm, 10% mist, 2770 RPM

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