Turbulent Boundary Layer in Diverging Flow : The 3rd Report, Universal Velocity Distribution near the Wall

Abstract

Measurements of skin frictions and velocity profiles in turbulent boundary layers with adverse pressure gradients are presented. The skin friction was measured by a surface Pitot tube of the stanton type which was calibrated under various pressure gradients. It is said that all velocity distributions near the wall expressed in the universal form u/u^* vs. u^*y/ν are almost the same irrespective of pressure gradient. Our experiments showed that this relationship holds up to a short distance before the separation point. However, near the separation point (H>1.7) the value of coefficient a₁ in the universal velocity distribution u/u^*=a₁+a₂log₁₀ (u^*y/ν) diminished as shown in Fig.12 and the measured values of skin friction were greater than that predicted by the equation of Ludwieg and Tillmann.