Film Cooling Injection Hole Geometry: Hole Shape Comparison for Compound Cooling Orientation
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Film cooling, for gas turbine blades or other applications, is done by injecting cool air through a row of holes in a solid wall, past which hot gas is flowing. To investigate the effect of hole shape directly, the present experimental and computational study compares the film cooling effectiveness of two sets of compound-oriented holes, one square and the other round, both placed (alternatively) in a plane wall. Both have the same cross-sectional area, and both are tested in the same facility at the same three blowing ratios R: 0.5, 1.0, and 1.5. Numerical simulations are made using the standard k- turbulence model. Film cooling effectiveness is measured using a flame ionization detector. Results show that the holes perform quite differently, the square holes being slightly superior only very close to the injection point and only at low R. For all higher blowing ratios and larger downstream distances investigated, the round holes are better due to the lower integrated momentum flux away from the wa ll plane at the hole exit. The marked differences between the effectiveness of round and square holes confirms that hole exit geometry is an extremely important factor in film cooling design, even at compound orientation angles.
