Upstream Condition Effects on Turbulent Boundary Layers Subject to Favorable Pressure Gradients

Abstract

The effects of the upstream conditions in favorable pressure gradient boundary layers are studied by carrying out an experiment using laser-doppler anemometry over multiple traverses along a smooth plate. A set of upstream conditions composed of upstream wind tunnel speed, tripwire location, and the strength of the pressure gradient is analyzed. The similarity analysis of the equations of motion for pressure gradient flows is used to obtain the scales for the outer flow. For this study, the mean deficit profiles show a small dependence on the strength of the pressure gradient when scaled with the freestream velocity U ∞ . Second, the upstream conditions effects are removed from the velocity deficit profiles when normalized by the U ∞ δ*/δ scaling. However, the Reynolds stress profiles show the effects of upstream conditions and the strength of the pressure gradient. Finally, these favorable pressure gradient flows are found to be nonequilibrium flows because the pressure parameter A is not constant. In addition, three quadrants are found to describe all pressure gradient flows: one for adverse pressure gradient, one for favorable pressure gradient, and one for quasi-laminar flows, where different values are obtained and these are dependent on the experimental conditions. The quadrants are obtained by plotting log (U ∞ /U ∞i ;) versus log(δ/δ i ).