One of the main reserves of improvement in fuel efficiency of ground vehicles is reduction of aerodynamic drag constituting (side by side with the resistance of rolling) the principal component consuming normally a bulk of vehicle’s power to overcome it.
Conventional ground vehicles (including cars, SUVs, trucks, etc.) aerodynamically speaking represent bluff bodies: i.e., bodies characterized by separation of flow and high aerodynamic drag, while providing vehicles with low-drag streamlined bodies preventing separation of flow results as a rule in some unpractical shapes with excessive longitudinal dimensions (caused, e.g. by long smoothly tapering tails) that makes this way doubtful under regular traffic conditions.
The alternative solution of this problem is an Active Aerodynamic System that could form any required (favorable in terms of CD) artificial pattern of flow around vehicle through employment of aerodynamic principle of superposition of flows. The system comprises blowers, air ducts and nozzles ejecting air at certain areas of vehicle’s body.
Such system can be arranged completely within vehicle’s body and, so, it doesn’t require any changes in original shape of vehicle to improve its aerodynamic characteristics (i.e., reduce aerodynamic drag and consumption of power to overcome it) and fuel efficiency.
Operation of this system ultimately could result in formation of a new artificial pattern of flow corresponding to some streamlined body and covering the whole vehicle. However, in many cases it could be found more practical to employ a downscaled (low power and more compact) version of the system that would modify and improve pattern of flow around vehicle locally providing reduction of aerodynamic pressure on vehicle’s surfaces facing forward and raising pressure on surfaces facing aft.
Such simplified systems were tested in a wind tunnel in application to 1/8 model of a tractor-trailer and ¼ model of SUV. The trials revealed practical operability of the tested systems, potentialities to vary and reduce aerodynamic drag of vehicles in a very wide range (up to complete elimination) and to improve fuel efficiency by more than 20% at optimum parameters of ejection corresponding to reduction of drag by about 30%.