Direct Measurement of Wall Shear Stress With Mass Transfer in a Low Speed Boundary Layer

Abstract

A porous plate floating element is used to obtain direct measurements of shear stress in a transpired zero pressure gradient boundary layer from laminar asymptotic suction to blow-off. The thrust balance incorporates a feedback system which provides self centering of the porous element from zero shear stress up to the maximum encountered. Shear stress data obtained for suction and blowing conditions agree well with previously determined indirect data. The floating element data are well correlated by two equations, one for the suction mode, and one for the blowing mode, via simple modifications of an existing correlation.