基于浸入边界-格子Boltzmann通量求解法的椭圆柱流动特性分析

基于浸入边界-格子Boltzmann通量求解法，开展了雷诺数Re=100不同几何参数下单椭圆柱及串列双椭圆柱绕流流场与受力特性对比研究。结果表明，随长短轴比值的增加，单椭圆柱绕流阻力系数先减小后缓慢上升，最大升力系数则随长短轴比值的增大而减小；尾迹流动状态从周期性脱落涡到稳定对称涡。间距是影响串列圆柱及椭圆柱流场流动状态的主要因素，间距较小时，串列圆柱绕流呈周期性脱落涡状态，而椭圆柱则为稳定流动；随着间距增加，上下游圆柱及椭圆柱尾迹均出现卡门涡街现象，且串列椭圆柱临界间距大于串列圆柱。串列椭圆柱阻力的变化规律与圆柱的基本相同，上游平均阻力大于下游阻力；上游椭圆柱阻力随着间距的变大先减小，下游随间距的变大而增加，当间距达到临界间距时上下游阻力跃升，随后出现小幅度波动再逐渐增加，并趋近于相同长短轴比值下单柱体绕流的阻力。

Numerical simulations of flow over isolated and two tandem elliptical cylinders by immersed boundary-lattice Boltzmann flux solver

The paper carries out numerical simulations of incompressible flows over one isolated and two tandem elliptic cylinders at low Reynolds number by the immersed boundary-lattice Boltzmann flux solver(IB-LBFS).The method combines the immersed boundary method with the lattice Boltzmann method of single-relaxation-time type to enable the use of simple Cartesian mesh for simulation of the flow past complex geometries in laminar flow.After validating the correctness of this method, the influences of geometric parameters on flow wakes and mechanical characteristics are analyzed for isolated and tandem elliptic cylinders.For a single elliptic cylinder, the results reveal that, with the increase of axis ratio, the average drag coefficient decreases first and then increases and the maximal lift coefficient decreases.Meanwhile, the wakes change from periodic vortex shedding to the symmetric flow pattern.For tandem elliptic cylinders, the gap spacing is another key parameter besides axis ratio.when the gap spacing is small, the flow pattern of tandem cylinders presents a vortex street downstream the cylinders, but the wake pattern of elliptic cylinders is a steady flow.It means that the downstream elliptic cylinder can effectively suppress vortices shedding of upstream elliptic cylinder at small gap.With the increase of gap spacing, upstream and downstream circular and elliptic cylinder wakes all appear as Karman vortex streets.The critical gap spacing of elliptic cylinders is larger than cylinders''gap.The variation of the mean drag coefficient of tandem elliptic cylinders is similar to tandem cylinders.The upstream drag is greater than the downstream drag.With the increase of gap spacing, the upstream drag decreases but the downstream drag increases.And both upstream and downstream drags rise drastically till the gap reaching at the critical gap.With further increase of the gap spacing, the upstream and downstream drags show small scale fluctuation and then gradually increases to the drag value of a single elliptic cylinder at the same axis ratio.