Computational analysis of partially-covered cavity with and without side walls

A subsonic three-dimensional cavity with a cover over the first two-thirds of the length was simulated using Delayed Detached Eddy Simulation. Two geometric set-ups were investigated: one is a quasi-3D simulation, with no side walls and a spanwise-periodic boundary condition, and the other is a fully-3D simulation, with resolved no-slip side walls and a surrounding plate section. In both cases a large counter-rotating vortex pair was observed inside the cavity, and the unsteady shear layer over the open section of the cavity produces regular vortex shedding. However, the presence of the side-walls causes the vortices to quickly break down in the span direction; the simulation without side walls maintains stronger, spanwise-coherent vortices for a much longer time. In both simulations the frequencies were found to agree well with Rossiter-mode cavity resonance based on the open section of the cavity. However, the presence of the side walls shifts the dominant modes, from modes 2 and 4 in the spanwise-periodic simulation, to modes 1 and 2 in the side-wall simulation. The side walls also cause a strong resonance at the mode 1 frequency in the covered section of the cavity, which was not observed with the spanwise-periodic boundary condition.