Direct measurements of skin friction in a scramjet combustor

A direction experimental measurement was made of the skin friction in the turbulent boundary layer of three-dimensional supersonic combustor flows. A floating element configuration was designed to detect two components of the small tangential shear forces due to the flow passing over a nonobtrusive instrument. A cantilevered sensing head extending from a very sensitive piezoresistive displacement transducer simultaneously measured displacement in the axial and transverse directions to the flow. The small overall deflection means that no self-nulling is required. Consistently repeatable output from the gage during testing show the skin friction with supersonic combustion is higher than for a corresponding noncombusting flow. The results are probably accurate to within 10 percent for the mean streamwise component.