Flow features from the wake of a rotating sphere

The flow features in the wake of a rotating sphere is investigated numerically. Simulations are carried out at Reynolds numbers up to Re = 1000, with non-dimensional rotational rates \textbf{$\Omega $}= 0 to 1. The axis of rotation is orientated from \textit{$\alpha $} = 0 (streamwise rotation) to \textit{$\alpha $} = \textit{$\pi $}/2 (transverse rotation). At Re=250 and 300, the flow field could be steady or unsteady, depending on the value of \textbf{$\Omega $} and \textit{$\alpha $}. Phase diagrams of \textbf{(}CLx\textbf{,}CLy\textbf{) } and (CD\textbf{,}CL ) are used to illustrate the dynamics of the unsteady forces acting on a rotating sphere. By employing the phase diagram \textbf{(}CLx\textbf{,}CLy\textbf{)}, the direction of the resultant lift force can be shown to be dependent on the non-dimensional rotation rate. The shape of the curves which appear on the phase diagrams \textbf{(}CLx\textbf{,}CLy\textbf{) } are highly correlated to the behaviour of the vortical structures in the wake. This study will give a more complete picture of the physics associated with the incompressible flow past a rotating sphere.