Skin Friction Drag with Boundary Layer Combustion in a Circular Combustor

Abstract

Skin friction on the internal surface of a circular cross section supersonic combustor has been determined through the measurement of the total drag force on the combustor. The pressure drag and thrust acting on forward and aft faces was accounted for and the effect of tangential hydrogen fuel injection into the boundary layer in the combustor has been studied. Despite the pressure rise in the constant area duct, the drag force was not found to be higher with combustion than for a fuel-off experiment. Skin friction forces as low as 40% of the expected value for a boundary layer subject to the same pressure gradient but without combustion were measured. Comparison of the results with prediction from an an- alytical model by Stalker that incorporates film cooling and/or boundary layer combustion effects was made and varying agreement was found. For cases where the boundary layer thickness at the injection point was of the order of the injection step height, skin friction was found to be further reduced than for the cases where the boundary layer thickness was a quarter of the step height.