Skin Friction and the Inner Flow in Pressure Gradient Turbulent Boundary Layers

This investigation will look at multiple methods to determine the wall shear stress for several pressure gradient turbulent boundary layer flows, particularly favorable pressure gradient and zero pressure gradient. These methods include using the slope at the wall, the integrated bounary layer equation, momentum inte-gral equation and the Clauser method. In order to perform this study, 2D Laser Doppler Anemometry, (LDA), measurements of the velocity field near the wall for various streamwise positions have been car-ried out at the Chalmers L2 wind-tunnel. With the resulting wall shear stress calculations, the effects of pressure gradient and upstream conditions will be in-vestigated on the inner region of the velocity profiles and Reynolds stresses. As will be seen, the inte-grated boundary layer equation is the most accurate technique to determine the wall shear stress when di-rect measurements are not available. In addition, the velocity profiles show a mild effect of the pressure gra-dient. The Reynolds stresses show a large effect of the pressure gradient in inner variables, but not below, y+ < 30. The shape of the Reynolds stresses < v2> and < uv> components changes significantly due to the external pressure gradient, damping them as much as 40%, though the streamwise < u2> component ex-hibits an insignificant amount of change