Numerical Study fof New Control Method fir Cavity Flow Oscillations

我们研究了利用移动底壁对开口空腔内自维持振荡流动的主动控制。用有限差分方法求解了二维层流边界层上游空腔的不可压缩N-S方程，当空腔长宽比L/D=2.0时，空腔底壁以-0.2~0.2的无量纲速度切向移动。结果表明，壁面速度改变了空腔内的回流特性，回流的修正对改变分离剪切层的振荡特性起着重要作用。当壁面速度小于-0.1时，腔内两个循环涡变为一个顺时针方向的循环涡，从而完全抑制了自激剪切层振荡。当壁面速度大于0.19时，空腔的上下侧存在两个静止的涡，抑制了自激剪切层的振荡。腔长以0.1的间隔变化，范围从1.0到4.0。对于较小的空腔长度，L和1.6时，流动不会发生振荡，空腔内只存在一个回流涡。对于1.7lt；L和3.0型，剪切层以模式II振荡，并伴有两个或三个环流涡旋。对于长腔L和GT；3.1，腔内出现四个涡旋，振动模式从模式II切换到模式III。控制模拟的结果表明，移动底壁的控制方法抑制了几种空腔长宽比和不同振荡模式下的自持剪切层振荡。

We investigated the active control of self-sustained oscillating flow over an open cavity using a moving bottom wall. The incompressible Navier-Stokes equations were solved using finite difference methods for the two-dimensional cavity with laminar boundary layer upstream.We move the cavity bottom wall tangentially with nondimensional velocities ranging from -0.2to +0.2for the cavity aspect ratio L/D=2.0. The results shown that wall velocity changes the characteristics of recirculating flow in the cavity and that the modification of recirculating flow plays an important role in changing the oscillation characteristics of the separated shear layer. When the wall velocity is less than -0.1, two recirculating vortices change to one clockwise recirculating vortex in the cavity, so that the self-excited shear layer oscillations are completely suppressed. When the wall velocity is more than +0.19, two stationary vortices exist on the upper side and lower side of the cavity and the self-excited shear layer oscillations are suppressed.A series of computations are carried out for different cavity lengths. The cavity length is varied at 0.1 intervals, ranging from 1.0 up to 4.0. For small cavity length, L<1.6, the flow does not oscillate and only one recirculation vortex is present in the cavity. For 1.7 < L < 3.0, the shear layer oscillates in mode II with two or three recirculation vortices. For long cavities L >3.1, four vortices appear inside the cavity and the oscillation mode switches from mode II to mode III.The results of controlled simulations show that the self-sustained shear layer oscillations for several cavity aspect ratio and different oscillation modes are suppressed by our control method using moving bottom wall.