Drag Changes Associated with Coanda Device on a Tractor Trailer Model

The changes in the drag coefficient on a tractor trailer model due to the use of Coanda devices were determined experimentally. The results on a one-twenty-seventh scale model show a marked reduction in the drag. The drag reduction is a function of the freestream to Coanda jet velocity ratio.

The reduction in the drag force is due primarily to the change in momentum of the Coanda jet, and not due to the aerodynamic shaping or control of the wake. The reductions in the aerodynamic horsepower required for a full scale model would not overcome the increase in the mechanical horsepower required for the operation of the Coanda device.

The net effect of application of the Coanda device to Full scale models is expected to actually increase the required energy consumption of the vehicle. Therefore, the application of energizing the wake in this manner holds no immediate promise for practical application in vehicle aerodynamic drag reduction.