Reducing energy consumption of ground vehicles by active flow control

In U.S, the ground vehicles consume about 77% of all (domestic and imported) petroleum; 34% is consumed by automobiles, 25% by light trucks and 18% by large heavy duty trucks and trailers. It has been estimated that 1% increase in fuel economy can save 245 million gallons of fuel/year. Additionally, the fuel consumption by ground vehicles accounts for over 30% of CO2 and other greenhouse gas (GHG) emissions. Moreover, most of the usable energy from the engine goes into overcoming the aerodynamic drag (53%) and rolling resistance (32%); only 9% is required for auxiliary equipment and 6% is used by the drive-train. 15% reduction in aerodynamic drag at highway speed of 55mph can result in about 5-7% in fuel saving. The goal of this paper is to demonstrate by numerical simulations that the active flow control (AFC) technology can be easily deployed/retrofitted to reduce the aerodynamic drag of ground vehicles by 15-20% at highway speed. For AFC, we employ a few oscillatory jet actuators (also known as synthetic jet actuators) at the rear face of the ground vehicle. These devices are easy to incorporate into the existing vehicles with very modest cost. The cost may come down significantly for a large volume - in hundreds of millions, especially for ground vehicles. Numerical simulations are performed using the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations on solution adaptive structured grids in conjunction with a two-equation realizable k-ε turbulence model. The commercially available grid generator "GAMBIT" and the CFD solver "FLUENT" are employed in the simulations. Three generic ground vehicle configurations are considered in the simulations; the experimental data has been available for these configurations without and with AFC. The numerical simulations are in good agreement with the experimental data. These studies clearly demonstrate that the AFC techniques can be effectively employed to achieve significant reduction (10-15%) in aerodynamic drag of ground vehicles thereby reducing the fuel consumption by 5-7%.