Film Cooling on a Concave Surface: Influence of External Pressure Gradient on Film Cooling Performance

摘要

The film cooling performance on a concave surface with zero and favorable pressure gradient free-stream flow was investigated experimentally. Adiabatic film cooling effectiveness values were obtained for five different injection geometries, three with cylindrical holes and two with shaped holes. Heat transfer coefficients were derived for selected injection configurations. Air and CO2 injection were used to achieve a variation of the density ratio between coolant and free stream. Free-stream acceleration caused an increase in adiabatic film cooling effectiveness for the investigated injection configurations and boundary conditions. This increase is stronger for the results obtained with cylindrical holes. No significant effects of the free- stream acceleration on the Stanton number ratios were obtained during corresponding heat transfer experiments. The determined heat flux ratios or film cooling performance indicated that coolant injection with shaped film cooling holes is much more efficient than with cylindrical holes, especially at higher blowing rates. (1 table, 13 figure, 9 refs.).