Shear Stress Vector Measurement Using a Circular Sublayer Plate with Multiple Pressure Taps

Abstract

A local wall shear-stress vector measurement technique has been developed using a thin circular plate, referred to as a sublayer plate, which is attached to the wall in the sublayer of a near-wall turbulent flow. The pressure difference between the leading and trailing edges of the plate is correlated to the known wall shear stress obtained in the fully developed turbulent channel flow. A circular sublayer plate surrounded by eight pressure taps is designed to measure the wall shear-stress vector. The curvature of the round edge of the circular plate slightly reduces the sensitivity to the wall shear-stress magnitude in comparison with a rectangular plate. The circular plate can successfully detect the flow direction over a wide-range flow angle. The circular plate with eight pressure taps has a higher resolution in the measurement of the wall shear vector for a small angle of attack using the ratio of the pressure differences at two taps adjacent to the tap showing the maximum stagnation pressure.