  The present work investigates sidewall effects on the characteristics of
three-dimensional (3D) compressible flows over a rectangular cavity with aspect
ratios of $L/D=6$ and $W/D=2$ at $Re_D=10^4$ using large eddy simulations
(LES). For the spanwise-periodic cavity flow, large pressure fluctuations are
present in the shear layer and on the cavity aft wall due to spanwise vortex
roll-ups and flow impingement. For the finite-span cavity with sidewalls,
pressure fluctuations are reduced due to interference to the vortex roll-ups
from the sidewalls. Flow oscillations are also reduced by increasing the Mach
number from 0.6 to 1.4. Furthermore, secondary flow inside the cavity enhances
kinetic energy transport in the spanwise direction. Moreover, 3D slotted jets
are placed along the cavity leading edge with the objective of reducing flow
oscillations. Steady blowing into the boundary layer is considered with
momentum coefficient $C_\mu=0.0584$ and $0.0194$ for $M_\infty=0.6$ and $1.4$
cases, respectively. The three-dimensionality introduced to the flow by the
jets inhibits large coherent roll-ups of the spanwise vortices in the shear
layer, yielding $9-40\%$ reductions in rms pressure and rms velocity for both
spanwise-periodic and finite-span cavities.
