Computational Aeroacoustic of Buffeting Phenomena Coming From an Open Sunroof

In the last years aeroacoustics has become one of the most active research fields in the transportation industry: the success of new models of airplanes, trains, trucks and cars relies more and more on the level of comfort for passengers, where acoustic comfort plays a major role. Moreover, the progress in numerical techniques and in available computing power, has provided industry with more efficient and robust simulation techniques in the field of aerodynamically generated sound. Great efforts were spent by CRF in the past years in the development of tools for the prediction of noise levels associated with aeroacoustic phenomena and simulation of turbulent unsteady phenomena became possible (or even practical) much earlier than it was expected, even if limited to simplified cases. Today with the use of the supercomputing environment it is becoming possible to face real problems in realistic configurations, like aerodynamic noise from a complete car or from fluid-acoustic resonance of cavities. One example of this last case is represented by the buffeting phenomenon. It takes place when opening the sunroof, external flow comes into contact with the passenger compartment cavity. When the fluid-dynamic fluctuations of the external flow match one of the acoustic modes of the internal cavity resonance takes place: acoustic oscillations feed energy to the fluid-dynamic oscillation of the external flow, which respond with the generation of coherent structures (vortices traveling through the sunroof opening) that in turn feed more energy back to the acoustic modes, until an equilibrium is reached and steady oscillations take place. This paper describes recent development of aeroacoustic simulation of this phenomena, giving an overview on data coming from computation on sunroof systems with and without deflector and comparing these results with experimental data measured into wind tunnel.