Parallel numerical simulations of subsonic, turbulent, flow-induced noise from two- and three-dimensional cavities using computational aeroacoustics.

摘要

In this thesis, the phenomenon of flow-induced noise from two- and three-dimensional cavities is investigated with the use of computational aeroacoustics (CAA) and parallel computers. This is part of on-going research to further the current understanding of airframe noise. The field of CAA has shown great promise in the solution of primarily inviscid noise generation and wave propagation problems that are governed by the Euler equations. In the present study, these ideas are extended to the solution of the Navier-Stokes equations in multi-dimensions where the acoustic and flow fields may be influenced by viscous effects. A higher-order dual dual time-stepping algorithm is proposed in which efficient acceleration techniques typical of explicit steady-state solvers are extended to time-accurate calculations.; Flow over two-dimensional cavities with various geometric configurations, flow speeds, and types of incoming boundary layers are examined. For deep and moderately shallow cavities, the flow is oscillating in the shear layer mode. As the length-to-depth ratio of a two-dimensional cavity increases, the cavity flow is observed to oscillate in the wake mode. These phenomena are examined in detail. Correlation analyses of fluctuating pressure are carried out to estimate the convection speed of the large-scale structures, and the prediction is compared with experiment and theory. The use of a simple wall function at the upstream wall in order to alleviate the use of a full turbulent grid is assessed. Strouhal numbers of discrete tones at various subsonic speeds are compiled and compare with experimental data and direct numerical simulation. A simulation of flow-induced cavity noise over a three-dimensional cavity is performed at subsonic speeds and a low Reynolds number. Fluctuating flow quantities are averaged and compare with the mean experimental data. It is shown that three-dimensional calculations are necessary to simulate the correct physical behaviors of shallow cavities at subsonic speeds.