A study of aeroacoustics of two-dimensional generic vehicle profile

A D-shaped body, an elongated rectangular cylinder with rounded leading edge embodying the cross-section of a generic car body, is a popular model used in vehicle aerodynamics studies. The previous research of flow past the D-shaped body aims to describe the wake unsteadiness and develop drag reduction strategies. In this paper, the focus is put on the sound generation from flow past the D-shaped body at low Mach number. It is studied by conducting direct aeroacoustic simulation (DAS), which solves unsteady, compressible Navier-Stokes equations in two dimensions, using the conservation element and solution element (CE/SE) method. The reason of modelling the flow by two-dimensional solution is that the early separation and shear layer formation over the trailing edge are observed consistent with predominantly two-dimensional coherent structures. The DAS solution is then validated against existing experimental and numerical data. Results show that the flow exhibits early separation near the leading edge and alternating vortex shedding, known as the von Karman vortex street, from the trailing edge. As a vortex sheds from one side, a negative pressure pulse forms at that side, while a positive pressure pulse forms at the opposite side. Thus, negative and positive pules are produced alternatively and sound pressure waves are generated on both sides. Their propagation is verified by the study of directivity and decay of sound pressure in the far field, deduced that the current far field definition is at least region further than one acoustic wavelength, that agrees well with the theoretical aeroacoustics theories. The present research conducts detail investigation into the sound generation and propagation mechanism of a two-dimensional generic vehicle profile and provides insight into the noise reduction strategies for automobile.