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

摘要

A Fourier-Chebyshev spectral collocation method is used to compute the flow past a steadily rotating sphere subjected to a uniform cross flow. The simulations are performed at Reynolds numbers Re = 100,250 and 300, where the Reynolds number is based on freestream velocity and sphere diameter. These Reynolds numbers cover three different flow regimes for a stationary sphere, from steady axisym-metric, steady planar-symmetric to unsteady planar-symmetric. The effect of varying the rotation axis angle, α, on the laminar flow structures and time-averaged hydrodynamic forces is investigated over a range of non-dimensional rotation rates, Ω.~* This study reveals the time-averaged flight path of a solid rotating particle.rnAt 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, C_D and C_L. For all Ω~* considered, C_D and C_L 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, C_D and C_L follow the same trend as at Re = 100. The increase in Re dramatically reduce the C_D compared to the same Ω~* and α at Re = 100. C_L shows a more complicated behaviour as Re increases.