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Research Papers: Heat Transfer Enhancement

# Computational Analysis of Surface Curvature Effect on Mist Film-Cooling Performance

[+] Author and Article Information
Xianchang Li1

Department of Mechanical Engineering, Lamar University, Beaumont, TX 77710xianchang.li@lamar.edu

Ting Wang

Energy Conversion & Conservation Center, University of New Orleans, New Orleans, LA 70148-2220

1

Corresponding author.

J. Heat Transfer 130(12), 121901 (Sep 15, 2008) (10 pages) doi:10.1115/1.2970071 History: Received August 29, 2007; Revised April 16, 2008; Published September 15, 2008

## Abstract

Air-film cooling has been widely employed to cool gas turbine hot components, such as combustor liners, combustor transition pieces, turbine vanes, and blades. Studies with flat surfaces show that significant enhancement of air-film cooling can be achieved by injecting water droplets with diameters of $5–10 μm$ into the coolant airflow. The mist/air-film cooling on curved surfaces needs to be studied further. Numerical simulation is adopted to investigate the curvature effect on mist/air-film cooling, specifically the film cooling near the leading edge and on the curved surfaces. Water droplets are injected as dispersed phase into the coolant air and thus exchange mass, momentum, and energy with the airflow. Simulations are conducted for both 2D and 3D settings at low laboratory and high operating conditions. With a nominal blowing ratio of 1.33, air-only adiabatic film-cooling effectiveness on the curved surface is lower than on a flat surface. The concave (pressure) surface has a better cooling effectiveness than the convex (suction) surface, and the leading-edge film cooling has the lowest performance due to the main flow impinging against the coolant injection. By adding 2% (weight) mist, film-cooling effectiveness can be enhanced approximately 40% at the leading edge, 60% on the concave surface, and 30% on the convex surface. The leading edge film cooling can be significantly affected by changing of the incident angle due to startup or part-load operation. The film cooling coverage could switch from the suction side to the pressure side and leave the surface of the other part unprotected by the cooling film. Under real gas turbine operating conditions at high temperature, pressure, and velocity, mist-cooling enhancement could reach up to 20% and provide a wall cooling of approximately 180 K.

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## Figures

Figure 2

Meshes of partial domain and details near injection holes (with grid adaptation)

Figure 3

Flow pattern and temperature distribution

Figure 4

Comparison of air-only leading-edge adiabatic cooling effectiveness with that on a flat surface with the same nominal blowing ratio of 1.33

Figure 5

Droplet trajectories versus jet flow pathlines for leading-edge mist cooling

Figure 6

Enhancement of adiabatic cooling effectiveness by injecting mist with the nominal blowing ratio of 1.33

Figure 7

Effects of the droplet size and mist concentration on film-cooling enhancement at the leading edge

Figure 8

Effect of the main flow incident angle on flow and temperature distribution close to the leading edge

Figure 9

Effect of the main flow incident angle on adiabatic film-cooling effectiveness near the leading edge

Figure 1

Schematic of film cooling and computational domain: (a) film-cooling concept, (b) 2D cases, and (c) 3D cases

Figure 10

Effect of elevated operating conditions on mist film-cooling performance of the turbine blade leading edge

Figure 11

Flow pattern and temperature distribution of film cooling under the curvature effect on the pressure and suction sides

Figure 12

Comparison of air-only film-cooling effectiveness on flat and curved surfaces with a nominal blowing ratio of 1.33

Figure 13

Enhancement of film cooling with mist injection on concave and convex surfaces

Figure 14

2D droplet trajectories and vapor concentration in mist film cooling with concave and convex surfaces

Figure 15

Temperature distribution of air-film cooling on 3D leading-edge surface

Figure 16

Adiabatic cooling effectiveness of 3D leading-edge film cooling and its enhancement with mist injection

## Errata

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