Numerical investigation of Magnus effect on dimpled spheres

Direct numerical simulations of spinning dimpled spheres at three distinct flow regimes, subcritical, critical, and supercritical, are reported. A highly efficient, structured, and finite-difference solver in cylindrical coordinates is utilized, together with an embedded boundary formulation to impose the proper boundary conditions on the solid surface. The results exhibit all the qualitative flow features that are unique in each regime, namely the drag crisis and the alternation of the Magnus effect. In the critical regime, and for a certain range of rotation rates and Reynolds numbers, a negative lift force is produced. For all cases we provide quantitative evidence and analysis of the detailed mechanics of separation and its impact on the aerodynamic force generation.