An experimental investigation of the effect of initial shear stress distribution on a separating turbulent boundary layer

An experimental investigation of low Mach number turbulent boundary layers entering an adverse pressure gradient and flow to separation is described. Trials were run in a closed loop wind tunnel equipped for isothermal conditions and hot-wire anemometry. Meshes with 30.3 percent solidity were installed, together with a telescoping inlet duct and a variable height wall fence to induce separation. Static pressure taps defined wall pressure distributions and the boundary layer total pressure profile was characterized with a pitot tube. Mean velocity and turbulence data were obtained with a hot wire anemometer. Initial conditions vanished quickly with separation onset. A transverse length scale that incorporates the pressure gradient is proposed. The results are concluded to be useful for diffusers, airfoils, and subsonic diffusers.