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.
These vortex patterns are similar to the numerical flow patterns obtained by the direct integration of the unsteady, incompressible Navier-Stokes equations.
As a result, it is found that an effective configuration parameter on aerodynamic drag is related to wake patterns.