Turbulence effect on laminar separation on a circular cylinder

A smooth circular cylinder in crossflow at subcritical Reynolds numbers was studied. Results show that the interaction of incident turbulence with the initial laminar boundary layer modifies the characteristics of the mean surface pressure distribution, delays the separation and reduces the drag. These changes exhibited a distinct dependence upon the Reynolds number-background turbulence combination and result, from the energizing of the initial laminar boundary layer by penetrating turbulence concentrated at scales commensurate with its thickness. Energy-containing eddies form a coherent substructure near the cylinder stagnation zone which ensures a continual supply of turbulent momentum and energy to the boundary layer. The incident turbulence-boundary layer interaction mechanism is supported by correlations among characteristics of the mean surface pressure distribution and the position of the separation point with a turbulence intensity parameter and a turbulent separation parameter.