Transient Vehicle Aerodynamics In Four-car Platoons

The vehicles in a platoon will experience transient aerodynamic forces as vehicles leave and join the platoon at various locations. A platoon of scale vehicle models is placed in a wind tunnel and measurements are made of the transient forces and moments as one of the vehicles is moved into and out of the platoon. The results from the wind tunnel experiments will allow the computer vehicle control algorithms to better predict the transient aerodynamics the vehicles in the platoon will encounter during leaving and joining maneuvers. \par Since a lane change (either leaving or joining a platoon) maneuver occurs on the same time scale as changes in the flow field, characterization of the transient forces and moments becomes of paramount importance. In these experiments, one vehicle is moved out of and into the platoon at six different accelerations to simulate lane changes at six different time scales, the longest (smallest acceleration) representing the static case and the shortest (largest acceleration) representing half of the nominal time of an actual lane change. Measurements are made with the displaced vehicle as each of the four members of the platoon. The increase in the drag on the remaining cars in the platoon as one vehicle leaves confirms that the close spacing between vehicles in a platoon results in streamlined flow. All of the cars experience side forces and yawing moments resulting from the interrupted flow field caused by the displaced car. These effects are more pronounced on a platoon of boxes, bluffer shapes. These forces and moments are summarized here as nondimensional coefficients plotted with the nondimensional lateral displacement of the maneuvering vehicle.