The coupling between high-amplitude wall-pressure peaks and flow structures, especially in the near-wall region, was studied for a zero-pressure-gradient turbulent-boundary-layer flow and for the flow in the interior of artificially generated turbulent spots. By use of an ‘enhanced’ conditional averaging technique it was shown that buffer region shear-layer structures are to a high degree responsible for the generation of large positive wall-pressure peaks. The relation was proved to be bi-directional in that strong shear layers were shown to accompany positive pressure peaks and correspondingly that large pressure peaks were associated with shear-layer structures detected in the buffer region. This also indicates a link between the wall-pressure peaks and turbulence-producing mechanisms. The pressure-peak amplitude was found to scale linearly with the velocity amplitude of the generating flow structure, indicating that a dominating role here is played by the so-called turbulence – mean shear interaction. The large negative wall-pressure peaks were found to be associated primarily with sweep-type motions. All essential features of the relation between wall-pressure peaks and flow structures in artificially generated spots in a laminar boundary layer were found to be identical to those in the equilibrium turbulent boundary layer.

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Brake noises generated during vehicle operation are caused by nonlinear structural behavior that is difficult to model analytically. Noises, predominantly contact related, falling in this group can be classified into two categories based on the frequencies at which they occur: (1) brake squeal in kHz ranges; (2) brake moan and groan in 100–300 Hz range. These noises may often be accompanied by structural instability caused by some, if not all, of the following phenomena: (1) lining deformation; (2) negative slope in friction-velocity characteristic; and (3) stick-slip. In addition to the aforementioned phenomena, coupled resonance of brake components is also a necessary condition of the brake-noise generation. Currently, vehicle brake-noise design prevention is still based on a trial and error basis. No reliable design prevention tool is yet established. Although computer simulations were sometimes used to predict the structural instabilities, no clear understanding of the link between structural instabilities and radiated noise has been established. The major challenge to automobile noise control engineers will be to establish a noise radiation model which could identify the influence of the key design parameters on the noise level.

Although automobile wind noise performance keeps improving, some fundamental aspects of wind noise generation and transmission paths remain uncertain. This paper raises issues to be solved in vehicle shape related wind noise root cause understanding and prevention. Wind noise mechanisms such as the generation of vehicle body wall pressure fluctrrations (pseudo-noise) and their interaction with body structures, resulting in panel vibration, which radiates as noise, are described. Challenge issues such as the evaluation of the relative importance of low wave number versus convective contributions of pseudo-noise to structural excitation are discussed.