Theoretical and experimental investigation of the aerodynamic noise generated by air flows through car windows

Motor vehicle internal noise is due to the following sources: a) exhaust duct, b) aerodynamic friction, c) mechanical structures vibrations, d) rolling tyres noise. Aerodynamic noise may be particularly disturbing at open-windows conditions. A measurement campaign has been carried out in order to characterize the aerodynamic noise due to air flows through vehicle windows. A commercial car has been equipped with silent tyres and insulating cowlings in order to minimize c) and d) noise contributes; tests have been led on a downward street at low engine regimes in order to maximize b) noise contribute with respect to the a) one. Noise levels have been measured at the driver ears by varying vehicle speed and windows opening surface. Measurements results have shown that noise components frequencies values depends on the following physical parameters, in according to the theory of Helmoltz resonator: vehicle speed, car internal volume, windows opening surface. Such a theory may be conveniently employed to model the vehicle internal noise.