Acoustic field propagation in a confined environment for classic flow/aero-acoustics phenomena

The goal of my research is the aeroacoustic numerical and experimental characterization of the absorption and transmission phenomena of the acoustic field in confined subsonic flow application. Concerning the absorption phenomena, a validation and improvements of a recently developed Time Domain Impedance Formulation based on Recursive Convolution has been carried out. This formulation has been implemented in an in-house time-domain Runge-Kutta Discontinuous Galerkin (RKDG) Linearized Euler Equations (LEE) solver. The previous formulation has been improved to account for the presence of non-uniform sub stages within the uniform time step in the Runge-Kutta time integration scheme. At first, the boundary condition has been validated on the test case of a 2D lined rectangular duct without flow, with uniform mean flow (up to Mach number 0.2) and with a non-uniform mean flow. The RKDG results are compared with an analytical reference solution for the problem under consideration. In a second stage the simulation have been repeated on the case of 3D circular duct fully lined.

The study of the transmission phenomena of the acoustic field is focused on the car underbody environment.  Due to the development of a new generation of quieter engines, aerodynamic noise is identified as the major source of noise at driving speed above 100kph. The sound is transmitted towards the cabin as the result of a structural excitation of flexible structures by pressure fluctuations. Among the variety of aeroacoustic sources contribution, very few is known about underbody phenomena and in particular on the flow confinement effects on the lower surface excitation and on the vehicle interior acoustic. On my work I will concentrate on the design of a dedicated test rig that aims to reproduce a car underbody environment (flow confinement, reverberation, flexible plate connected to a rigid box, flow separation and reattachment) as well as on the development of new experimental source identification strategy based on sensors array acquisitions. The new strategy will be, at first, tested on numerical cases representative of a reverberant environment both for acoustic sources without flow and then including the convective effect of a uniform flow on the acoustic sources. Then the same procedure will be experimentally repeated by means of a test rig where 6 different known sources will be activated and detected. Finally the strategy will be used to detect ‘’unknown” aeroacoustics sources. I will then concentrate on the transmission of noise inside the car due to vibrations of separated/reattached flow or turbulent boundary layer (TBL) excited panels. At first, the characteristic of the excitation generated in the dedicated test rig will be experimentally analyzed by means of hot wire as well as PIV investigations, then different panel configurations will be analyzed in order to reduce the noise generated inside the panel back cavity.