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Notchback models generally have more complicated flow patterns than box models. This leads to intricate infuluence of rear geometry of Notchback on aerodynamic drag. Therefore, based on understanding of wake structure, flow phenomena for reducing the drag can be analyzed. This paper analyzes the influence of geometry of rear portion on the drag by means of 1/5 scale notchback models. For fastback models, at certain critical angle of the rear window the drag shows a sharp peak. For notchback models, it is found that some combination of the angle of rear window and the height of trunk deck shows simillar maximum in the drag. Moreover, the flow visualization and the detailed measurements of velocity fluctuation clarify typical vortex patterns of wake, which are an arch-type vortex behind the rear window and the trailing vortex behind the trunk deck.

The wind-noise-level in the cabin of a vehicle depends on the magnitude of the aerodynamically generated noise and noise isolation characteristics. Therefore, one good way to reduce the wind-noise-level in the cabin is to minimise the acoustic noise itself generated by the turbulent air flow around the vehicle at high speed cruising. This paper describes the relation between the turbulent flow and the aerodynamic noise as well as how to estimate the magnitude of aerodynamic noise, especially around A-pillar of a production vehicle. First, the flow visualization and the detailed measurements of flow clarify the vortex structure generated around A-pillar and side window. Secondly, sound pressure fluctuations measured on the side window surface are discussed in relation to the vortex structure. Lastly, in order to estimate the order of the magnitude of aerodynamic noise we, propose physical parameters given by approximating the solution of Lighthill's equation.