Aeroacoustic analysis of automotive roof crossbars through on-track acoustic measurements

This work concerns the noise radiated by crossbars installed on the roof of automotive vehicles. The Reynolds numbers analyzed range between 98,000 and 147,000 based on the crossbar chord. Through a comparison of results obtained in an aeroacoustic wind-tunnel, we demonstrate that on-track sound pressure measurements from a single in-flow microphone are suitable to study the aeroacoustics of crossbars under realistic operational conditions. The current investigation presents noise measurements by reference profiles such as elliptic and circular crossbars, as well as a NACA 0012 airfoil. Results from the elliptical crossbar show both tonal and broadband components in the noise spectra, combining features observed for the circular bar and the airfoil. For higher Reynolds numbers, the tones observed in the elliptical profile are broad and free of harmonics, similar to those observed for the NACA 0012. The influences of the leading and trailing-edge shapes of the elliptical crossbar on the radiated noise are presented together with the effects of the angle of attack. A thinner trailing edge leads to a reduction in the tonal noise followed by an increase in the broadband content. On the other hand, a blunter leading edge reduces the broadband noise, especially for higher frequencies. Positive angles of attack provide a reduction in both tonal and broadband noise components for the elliptical crossbar, particularly at lower Reynolds numbers.