利用上游槽道对角区马蹄涡的控制

在平板上放置圆柱形成角区流动,利用布置在圆柱上游平板上的二维和三维槽道来控制或削弱角区马蹄涡,采用风洞试验和数值模拟开展研究。结果表明,二维和三维槽道均能推迟边界层的分离,使圆柱根部马蹄涡的强度减弱、尺度减小;同时槽道上游压力和逆压梯度均有所下降,槽道下游压力显著升高而逆压梯度总体降低。二维槽道对马蹄涡强度的削弱为61.15%~66.51%,而三维槽道对其削弱为66.65%~80.93%。讨论了三维槽道参数(包括槽道宽度、深度以及其中心线与圆柱中心距离)对控制效果的影响。槽道与圆柱的距离在对马蹄涡的控制中起主导作用。槽道控制的机理是,由于槽道的抽吸效应使得其上游靠近壁面的边界层中涡量较高的流体被卷吸入槽道形成槽道涡,槽道涡由三维槽道输运到下游。同时,随着槽道与圆柱的距离减小,更多的边界层流体流入槽道内。正是上述"槽道效应"使得槽道下游的逆压梯度降低,马蹄涡强度减弱,分离区范围减小。

Junction flow horseshoe vortex control based on upstream cavity

Two and three dimensional cavities have been studied by experimental and numerical simulation to control horseshoe vortex formed when the flow passes a cylinder-flat plate junction.The cavity is located on the flat plate upstream of the cylinder.The results indicate that both two and three dimensional cavities can delay boundary layer separation and weaken the horseshoe vortex.At the same time,the upstream surface pressure and adverse pressure gradient of cavity are both reduced,and at the downstream the pressure is increased while the global adverse pressure gradient is reduced.The study also indicates that the two dimensional cavity can reduce about 61.15％-66.51％,while the three dimensional cavity can reduce 66.65％-80.93％,of the horseshoe vortex strength.The effect of cavity geometry parameters,including distance,width and depth,is discussed.It is shown that the cavity distance plays major role in weakening the horseshoe vortex.The mechanism for controlling the horseshoe vortex by cavity is discussed.It is shown that the sub-layer of the incoming boundary layer which contains high vorticity is swallowed into the cavity to form the cavity vortex.The cavity vortex is transported to the downstream of the junction.As the cavity gets closer to the cylinder,more sub-layer of boundary layer will be swallowed into cavity.It is this cavity-effect that reduces the surface adverse pressure gradient upstream of the cylinder and diminishes the horseshoe vortex and separation region.