Numerical simulation of spiral vortices on rotating sphere

Flow characteristics and fluid force on a sphere rotating along with an axis parallel to mean airflow were investigated using Large Eddy Simulation at around critical Reynolds numbers of 200,000. As a result of the simulation, a decrease in the numbers of spiral vortices and striped pressure distributions on the sphere were visualized depending on the rotation speed of the sphere even though the sphere is exposed to the same Reynolds number condition. Also, as the rotation speed of the sphere increased, the relative velocity between the mean flow and the surface of the sphere increased, subsequently, the length of the spiral vortex decreased due to the boundary layer transition on the sphere's surface. The shift of the separation point depending on the rotation speed is also discussed from the viewpoint of this boundary layer transition on the surface.