Numerical Study fof New Control Method fir Cavity Flow Oscillations

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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.