Effect of Passive Flow-Control Devices on the Drug of a Tractor-Trailer Model

The aerodynamic drag of tractor trailers is responsible for approximately half of the fuel consumption at highway speeds (55m.p.h.). Thus, it is important that vehicle drag be reduced in order to reduce operating costs and to conserve fuel. The purpose of the subject research conducted in the Old Dominion University Low-Speed Wind Tunnel was to determine the effect of various add-on flow-control devices, such as a cab-mounted flow deflector and gap seals between the tractor and the trailer. In addition, the effect of trailer rear-edge shaping has been studied. This was accomplished by contouring the trailer's rear end. It has been previously demonstrated by other researchers that introducing longitudinal vortices into the wake of a blunt body energizes the flow, resulting in a base pressure increase and a decrease to the total pressure drag. Various types of vortex generators have been investigated, including V-grooves, wishbones and doublets. Total drag on the 1/16 th scale tractor trailer model has been measured with a one-dimensional drag balance especially designed for drag-reduction research. Tests have been conducted up to speeds of 80 m.p.h. Findings of this study indicated that an elliptical rear edge modification can reduce drag of a baseline model by 20%. Wishbone and doublet vortex generators as well as longitudinal V-grooves have shown a drag reduction up to 15% on the baseline model.