错列双圆柱下游圆柱的升力机理

采用大涡模拟(LES)的方法,在雷诺数Re=1.4×10~5时,研究了间距P/D=4(P为圆心间距,D为圆柱直径)、风向角0°～90°的错列双圆柱的气动力特性和干扰流态,从流场角度分析了下游圆柱受到平均升力和脉动升力作用的流场机理.结果表明:随着风向角的增大,两个圆柱的干扰流态依次为旋涡撞击流态、旋涡撞击和剪切层干扰流态、剪切层干扰流态、尾流干扰流态;在旋涡撞击流态、旋涡撞击和剪切层干扰流态下,上游圆柱的旋涡与下游圆柱发生强烈的撞击,导致下游圆柱的脉动升力远大于单圆柱;在剪切层干扰流态下,下游圆柱受到显著的平均升力作用,下游圆柱风压停滞点的偏移以及上游圆柱的旋涡与下游圆柱间隙侧剪切层(或旋涡)的相互作用,是下游圆柱受到平均升力作用的两个原因.

Lift Mechanism of Downstream Cylinder on Two Staggered Circular Cylinders

In order to clarify the lift mechanism of downstream cylinder at a high Reynolds number Re=1.4×105, the large eddy simulation (LES) method was adopted to investigate the aerodynamic forces and flow pattern of two staggered circular cylinders. The ratio of center to center pitch (P) to the diameter of cylinder(D) is 4 and the incidence angle is 0° to 90°. The mean and fluctuating lift mechanisms of downstream cylinder were discussed as well. With the incidence angle increasing, the flow pattern of two cylinders is classified into the vortex impinging flow pattern, the vortex impinging and shear layer interaction flow pattern, the shear layer interaction flow pattern and the wake interaction flow pattern. For the vortex impinging flow pattern, the vortex impinging and shear layer interaction flow pattern, the vortex of upstream cylinder impacts with downstream cylinder, hence the downstream cylinder experiences a higher fluctuating lift than the single cylinder. For the shear layer interaction flow pattern, the downstream cylinder is subject to a significant mean lift, which is ascribed to the combined effects of two factors, i.e., the shift of stagnation point, and the interaction between the vortex of the upstream cylinder and the shear layer or vortex of the downstream cylinder.