Donavan, P., "Investigations of the Influence of Lower Frequency Aerodynamic Noise on Interior Cruise and Exterior Pass-By Sound Levels," SAE Int. J. Passeng. Cars - Mech. Syst. 5(3):1133-1142, 2012, doi:10.4271/2012-01-1554.
The results of a series of tests were performed that are used to investigate the contribution of aerodynamic noise to lower frequency passenger car interior and exterior cruise noise levels. Wind tunnel measurements were used to isolate aerodynamic noise from tire-pavement and engine noise and to indicate that the vehicle underbody is a significant source region for both interior and exterior noise. Comparing interior on-road measurements to the wind tunnel results, it was found that aerodynamic noise was slightly less than an equal contributor to cruise noise averaging 4.8 dB lower than the road levels between 50 and 400 Hz at a speed of 80 km/h. At 140 km/h, the difference dropped to 2.3 dB indicating that the aerodynamic noise was the major contributor. For exterior pass-by, aerodynamic noise levels were found to account for almost all of the noise measured during coast-by conditions in the frequency range from 50 to 400 Hz at 97 km/h. This finding was substantiated by additional pass-by testing using different tires on a variety of pavements. It was further found that aerodynamic noise was likely a partial contributor to pass-by noise levels at vehicle speeds as low 56 km/h. These influences were also indicted by comparing tire-pavement source levels measured on-board to the overall cruise and coast pass-by levels. Although the influence of aerodynamic noise will vary with tire design, vehicle design, pavement, and vehicle speed, this paper should provide motivation for considering it in both predicting and reducing interior and exterior noise.