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Experimental and computational results are presented that describe gaseous film-cooling performance of straight cylindrical cooling holes inside a cylindrical test section similar to a rocket combustion chamber. Experiments were performed using hot air as the core gas and gaseous nitrogen as the film coolant. A three-dimensional multispecies computational model using finite volume formulation has been developed and validated against the experimental data. Film-cooling performance is predicted for a variety of imposed geometrical parameters and blowing ratios. Results show local and spatially averaged performance change with blowing ratio due to differences in the magnitude of vortices created downstream of the coolant injection and the jet exit momentum. It is observed that higher mixing of coolant with the mainstream and high vorticity levels negates the presence of more coolant availability at higher blowing ratios and results in an optimum blowing ratio for a given geometric configuration. Higher effectiveness is obtained for the conjugate walls throughout the test section except at regions very close to the coolant injection. High conductive walls produced a negative heat flux condition immediately downstream of the coolant jet exit, indicating that a highly conductive wall is not a proper choice for internal wall-jet film-cooling applications. The results could provide useful input for analysis and optimization of straight cylindrical coolant holes.

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An experimental investigation is conducted to bring out the effects of coolant injector configuration on film cooling effectiveness, film cooled length and film uniformity associated with gaseous and liquid coolants. A series of measurements are performed using hot air as the core gas and gaseous nitrogen and water as the film coolants in a cylindrical test section simulating a thrust chamber. Straight and compound angle injection at two different configurations of 30°-10°and 45°-10°are investigated for the gaseous coolant. Tangential injection at 30°and compound angle injection at 30°-10°are examined for the liquid coolant. The analysis is based on measurements of the film-cooling effectiveness and film uniformity downstream of the injection location at different blowing ratios. Measured results showed that compound angle configuration leads to lower far-field effectiveness and shorter film length compared to tangential injection in the case of liquid film cooling. For similar injector configurations, effectiveness along the stream wise direction showed flat characteristics initially for the liquid coolant, while it was continuously dropping for the gaseous coolant. For liquid coolant, deviations in temperature around the circumference are very low near the injection point, but increases to higher values for regions away from the coolant injection locations. The study brings out the existance of an optimum gaseous film coolant injector configuration for which the effectiveness is maximum.