Effect of free-stream turbulence on the drag force on a flat plate

Abstract

The effect of intensity and length scale of turbulence on the mean and fluctuating drag forces on a flat plate normal to a boundary layer flow is investigated. Experiments were conducted at the University of Adelaide large wind tunnel to measure the drag force on flat plates of different areas. Two boundary layers of different depths were generated by spires and roughness elements to achieve a range of longitudinal turbulence intensities between 12% and 26% and integral length scales between 0.4 m and 1.22 m. The root-mean-square of the fluctuating drag coefficient was well correlated with a turbulence parameter defined as a function of turbulence intensity ( ) and integral length scale ( ). The results showed that both the fluctuating and the peak drag coefficients increased logarithmically with increasing the turbulence parameter such that increasing the turbulence parameter from 0.11 to 0.47 increased the peak drag coefficient from 1.73 to 3.