Flow Control on the Ahmed Body Vehicle Model Using Fluidic Oscillators

Aerodynamic drag accounts for a sizable portion of transportation energy consumption. Transportation of goods and people always involves moving objects through air, which leads to a force opposing motion. This force can account for more than 60% of power consumed by a ground vehicle, such as a car or truck, at highway speeds. There is a wide range of drag coefficient seen on ground vehicles with a strong correlation to vehicle shape. The shape of the vehicle is often determined by functional necessity or aesthetics, which places a limit on vehicle aerodynamic improvements. It is desirable to increase the aerodynamic performance of a vehicle with little penalty to these design considerations, which leads to the investigation of active flow control methods. Active flow control methods can involve a type of air jet at critical locations on the vehicle shell and require little to no shape modification. The focus of this experimental study is drag reduction on an Ahmed body vehicle analogue using a variety of configurations involving fluidic oscillators to promote attachment and reduce wake size. A fluidic oscillator is a simple device that converts a steady pressure input into a spatially oscillating jet. This type of actuator may be more efficient at influencing the surrounding flow than a steady jet. The model was tested in the OSU subsonic wind tunnel. Changes in drag were measured using a load cell mounted within the vehicle model. Different flow visualization methods were used to characterize the flow structure changes behind the model. A 7% drag decrease was realized with the 25° spanwise oscillator array configuration, attributed to the reduction of the closed recirculation bubble size. Testing showed that attachment is promoted on high angle configurations with a Coanda surface and steady blowing however this led to a drag increase, possibly due to the formation of longitudinal vortices. This indicates that future methods may require vortex control in conjunction with separation control to achieve a net base pressure increase on the high angle configurations.