Computational study of drag reduction of models of truck-shaped bodies in ground effect 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. Furthermore, the fuel consumption by ground vehicles accounts for over 70% of CO₂ and other greenhouse gas (GHG) emissions in U.S. Most of the usable energy from the engine (after accounting for engine losses) at highway speed of 55 mph 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 on generic truck models that the active flow control (AFC) technology can be easily deployed /retrofitted to reduce the aerodynamic drag by 15-20% at highway speed. It is important to note however that these estimates of drag reduction are based on CFD studies performed on simple generic truck models; for actual trucks the values will be much lower because of considerable complexity of the configurations. 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 at very modest cost. The cost may come down significantly for a large volume of actuators, 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- 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. In addition, a computational study is performed for one of the generic truck model to include the ground to evaluate its effect on aerodynamic drag without and with AFC. These studies clearly demonstrate that the AFC technique using synthetic jet actuators can be effectively employed to achieve significant reduction (10-15%) in aerodynamic drag with a potential of reducing the fuel consumption by 5-7%.