圆锥空腔内涡破裂现象的数值模拟

Numerical simulation of vortex breakdown in conical chamber

采用三维非定常的Navier-Stokes方程对底面驱动的密闭圆锥室内旋转层流流动中的涡破裂现象进行了数值模拟,分析了雷诺数和几何结构对圆锥空腔内涡破裂现象的发展规律的影响.利用有限体积法离散控制方程和SIMPLE算法实施计算,计算网格采用非结构化网格.根据数值模拟结果得出了圆锥室内涡破裂现象的发展特性.研究结果表明:当达到一定雷诺数时,圆锥室内中心轴线附近会出现一个低压的涡破裂区域,并伴随着局部流体回流;在所研究的雷诺数范围内,随雷诺数的增加,涡破裂气泡的尺寸先增大后减小直至消失,涡破裂气泡的位置沿中心轴向远离驱动面的方向移动;对于相同高径比的圆锥室,涡破裂现象出现和消失时的临界位置不随圆锥室几何形状的变化而变化;由涡破裂现象出现时的临界雷诺数的大小可知,圆锥室模型相对于圆柱室模型抑制了涡破裂现象的产生,且顶面直径最大时的圆锥室(H1/H=0)的抑制效果最好.

Vortex breakdown of swirl flow in an enclosed conical chamber with a rotating bottom wall was studied by numerical simulation,and the influences of Reynolds number and geometric parameters on the development mechanism of vortex breakdown phenomenon were analyzed. The flow was governed by the unsteady three-dimensional incompressible Navier- Stokes equations. The finite volume method was used to discretize the governing equations and the Semi-Implicit Method for Pressure Linked Equation( SIMPLE) algorithm was employed to couple the solutions of the system. The unstructured grid is applied to divide the computational domain. The development characteristics of vortex breakdown in the conical chamber derived from the simulation results are as follows: the low pressure region of vortex breakdown with local fluid recirculation would appear near the axis in the conical chamber when the Reynolds number reaches a critical value. As the Reynolds number increases further,the size of the vortex breakdown bubble increases first and then decreases until it disappears and it moves away from the driving surface within the parameter range studied. However,the positionwhere the vortex breakdown first appears and disappears doesn't change with the variation of the geometry for the conical chamber with the same aspect ratio. From the values of the critical Reynolds number when the vortex breakdown bubble appears,conical chamber suppresses the generation of vortex breakdown compared with cylindrical chambers and the conical chamber( H1/H = 0) with the maximum diameter of the top surface has the best suppress effect.