Flows over rectangular cavities exhibit various steady and unsteady phenomena, and are of concern in several engineering areas. When the incident flow is turbulent, high acoustic radiations are emitted. To evaluate the acoustic power radiated in the far field, a two-steps procedure is developped.
First, the unsteady, incompressible, high Reynolds number flow past a cavity is numerically investigated. The hydrodynamical 3D models which are used are based on standard Reynolds-averaged Navier-Stokes equations closed by some simple turbulence closure models. On another side, experiments are performed in a large water tunnel for different lenght to depth ratios ; flow visualization and fluctuating surface pressure measurements are made to chek numerical results which reveal some deficiencies. Morover, the extent of both numerical and experimental results combined to produce consistent input data for the ensuing acoustic model.
Secondly, a simple model, based on the Lighthill's acoustic analogy, incorporates the later data, to predict the amplitude and the frequencies of the far field noise. Measurements of the far field sound pressure level in a wind tunnel are also made at subsonic speed. A good agreement between the computed acoustic power in the far field and experimental data is shown.
As an interesting by-product of the hydrodynamical study consists in a refined classification of flow structures in the cavity when lenght-to-depth ratio increases. Three different flow configurations are observed. A quasi-2D flow is observed for a squared cavity. A transitional 3D flow charaterised by spanwise undulation of the main recirculating eddy is clearly shown for a lenght-to-depth ratio about 1,5. For a lenght-to-depth ratio above 2, the main recirculating eddy which is close to the downstream face of the cavity is purely 2D.