Virgil

An experimental study of techniques for modifying the surface shear stress, both mean and fluctuating, in turbulent boundary layers is reported. The surface shear along the test section of a 45.7 cm square wind tunnel, with a downstream expansion section, was determined by means of surface-hot-wire-heat-transfer-gauges. Turbulent boundary layers in both zero and adverse pressure gradients were evaluated.

Response of the flow variables to external driving forces is non-linear for shear flows. For the turbulent boundary layer case, surface shear stress fluctuations of magnitude as great as the mean value are observed. For flow near the surface Prandtl's turbulent boundary layer approach of employing averaged Reynolds equation and a turbulence closure model is insufficient to account for surf ace shear fluctuations. A model which incorporates a discrete...