Reynolds number scaling in a non-equilibrium turbulent boundary layer with mild adverse pressure gradient

High resolution laser Doppler anemometer measurements were acquired in a two-dimensional turbulent boundary layer over a four degree ramp at three momentum thickness Reynolds numbers: 3300, 14,100 and 20,600. The goal was to examine an adverse pressure gradient boundary layer far from separation in order to develop turbulent stress scalings to collapse the adverse pressure gradient and flat plate stress profiles over a range of Reynolds numbers. The flow develops as a flat plate boundary layer before being subjected to a varying pressure gradient along the length of a four degree straight ramp. Mean velocity measurements show a log law region for all velocity profiles. The stresses however are perturbed by the pressure gradient with the streamwise normal stress developing an extended outer layer plateau and the wall-normal stress displaying a growing outer layer peak. Scaling parameters are proposed to collapse the inner and outer layer regions of the normal stresses for both the adverse pressure gradient and flat plate profiles over the range of Reynolds numbers examined.