Effect of Roughness in the Development of an Adverse Pressure Gradient Turbulent Boundary Layer

An experimental study was conducted to examine the effect of surface roughness on the development of an adverse pressure gradient turbulent boundary layer. Hot-wire anemometry measurements were carried out using single and x-wire probes in the APG region of an open return type wind tunnel test section. The same experimental conditions (i.e. T∞, Uref, and Cp) are maintained between the smooth, k+= 0, and rough, k+= 41-60, cases. Results indicate that the mean velocity deficit and Reynolds stress profiles tend to increase with surface roughness. These effects of roughness were successfully removed from the outer mean velocity profiles using the Zagarola and Smits scaling, U∞δ*/δ. Using the integrated boundary layer equation, the skin friction was computed and showed a 58% increase due to the surface roughness effect. The effects of pressure gradient were found to be significant, of which, different profile trends with similar magnitudes were found for outer Reynolds normal stresses scaled with U∞