To eliminate additional complications introduced by mean flow, the vortex motion is assumed to be controlled by its image in the plate.
The accuracy and stability are illustrated by four test cases, namely the propagation of an acoustic wave in a medium at rest and in an uniform mean flow, the Taylor Green vortex decay and the vortex pair wall collision.
Results show that as the fence porosity increases, for the mean flow condition the vortex tends to be elongated and results in a reduction of the drag on the fence.
The vortex forms two excessive velocity maxima: one on the west associated with channel flow and the other on the east caused by the mean flow pressing on the slowdown vortex.
The primary interest here consists of evaluating the effects of mean flow convection, quadrupole sources and vortex shedding tonal noise on the overall sound pressure level (OASPL) of a NACA0012 airfoil at low and moderate freestream Mach numbers.
The experimental data show the strong effect of the geometric swirl number on mean flow characteristics, in particular with respect to vortex core size and the magnitude of the maximum tangential velocity.
In three-dimensional flows, care must be taken with the velocity-based formulation to avoid singular behavior associated with vortex stretching by the mean flow.
Building height variations may destroy or deviate 3D canyon vortexes and induced downward mean flow in front of taller buildings and upward flow behind taller buildings.
The low ratio "plate thickness/hole diameter" generates impedance levels dependent on the incident sound pressure level and the grazing mean flow (by a mechanism of nonlinear dissipation through vortex shedding), which penalises the optimal design of liners.
The acoustic perturbation equations are validated by computing a monopole source in a sheared mean flow, the sound generated due to a spinning vortex pair, and the sound generated by a cylinder in a crossflow.
