Laminar separation bubble in a spinning ball aerodynamics

We explore the flow past a spinning smooth ball at Re=1×105 for the spin factor range 0≤α≤1 using large eddy simulation (LES). When a spinning ball passes through a uniform flow field, an asymmetrical boundary-layer separation occurs along the retreating and advancing sides of the ball. This causes a deflection in the trajectory of the ball with a positive lift force, known as the Magnus effect. A counter-intuitive phenomenon was found at the critical Re regime and specific α due to the creation of a laminar separation bubble (LSB) on the advancing side, which reverses the direction of the lift, i.e., an inverse Magnus effect. The size of the LSB decreases as it moves upstream and finally disappears as α increases. The disappearance of LSB at a particular α is the starting point of the second Magnus effect, where the laminar boundary layer directly transitions to a turbulent condition. The LSB is associated with weak vortex shedding and high shedding frequency. The relaminarized zone is created on the retreating side while the laminar boundary layer shifts to a turbulent condition on the advancing side. Particular attention has been given to report mean force coefficients, Strouhal number of K–H instability of spinning cases, Strouhal number ratio, mean surface pressure coefficients, and wake dynamics.