Laminar flow structures from a rotating sphere: Effect of rotating axis angle

At Re = 100, the flow is always steady. The near-wake projected streamline patterns and pressure coefficient contours are topologically similar at α = 0 independent of the range of Ω∗ considered. As α increases, the near-wake recirculation bubble is either suppressed or shifted and thus affects the pressure recovery behind the sphere. This in turn affects both the drag and lift coefficients, CD and CL. For all Ω∗ considered, CD and CL increase as α increases and the increment is more pronounced at higher Ω∗. At Re = 250 and 300, calculations show both steady and unsteady wake structures. The state of the wake structures depends strongly on α and Ω∗. However, the time-averaged flow fields are qualitatively similar to Re = 100. As a result, the time averaged drag and lift coefficients, CD¯ and CL¯ follow the same trend as at Re = 100. The increase in Re dramatically reduce the CD¯ compared to the same Ω∗ and α at Re = 100. CL¯ shows a more complicated behaviour as Re increases.