For a vehicle traveling at highway speeds, turbulent flow produces a distributed force excitation on the greenhouse panels (for example, side windows and windshield), generating an acoustic field that acts on these panels. The greenhouse noise sources are complex transient-flow structures produced by flow separations and vortices resulting from various exterior geometry features such as the cowl, A-pillar, and mirror assembly. Accurate prediction of greenhouse noise sources requires predicting the time-varying flow structures and resulting wall pressure fluctuations on the greenhouse panels, including effects of small geometric details. The turbulent excitation, panel vibration, and acoustics are of widely varying length scales (the wavenumber spectrum), providing a significant technical challenge for accurate prediction over the important frequency range. Sound transmission of the exterior acoustic field to the interior is particularly important near the acoustic/structure coincidence frequency, and appears to be significant even though the turbulent wall pressure amplitudes far exceed those of the acoustic pressures.
