Recent Japanese Research on Three-Dimensional Bluff-Body Flows Relevant to Road-Vehicle Aerodynamics

Abstract

The introductory part of the paper contains a very brief discussion of recent research on automobile aerodynamics in Japan, touching on the progress and the prospects of aerodynamics in automobile design.

The major part is devoted to bluff-body research relevant to truck and bus aerodynamics. It mainly focuses on three-dimensional single-body configurations — bars of square cross-section having length-to-width ratios, L/W, from virtually 0 to 5. All edges of the bars were sharp, the longitudinal axis of each was aligned in the flow direction, and testing was performed in the absence of a groundplane. The drag coefficient changed considerably as L/W was varied from 0 to 5. The character of the variation of drag coefficient with angle of incidence, as well as that of lift coefficient with incidence, changed drastically when L/W reached 1.6. Flow visualization showed that this was accompanied by a change in the flow pattern, just as in the two-dimensional case of rectangular bars aligned perpendicular to the flow direction that was previously studied by the author.

The results of a preliminary experiment on two-body configurations representative of tractor-trailer systems are also presented. In this case the bodies were in tandem, each having its axis aligned in the streamwise direction, and the configuration was in close proximity to a simulated groundplane. The shape of the forebody and the rear of the afterbody were changed, while the gap and the afterbody length were varied. Only drag data at zero yaw angle is presented for these configurations.