An Examination of Active Drag Reduction Methods for Ground Vehicles
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Date
2013-05
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The Ohio State University
Abstract
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, which places a limit on vehicle aerodynamic
improvements. It is desirable to increase the aerodynamic performance of a vehicle with little
penalty in functionality, 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 is tested in the OSU subsonic
wind tunnel. Changes in drag are measured using a load cell mounted within the vehicle model.
Different flow visualization methods are used to characterize the flow structure changes behind
the model. A 7% drag decrease is realized with the 25 degree spanwise oscillator array configuration,
attributed to the reduction of the closed recirculation bubble size. Testing shows that attachment
is promoted on high angle configurations with a Coanda surface and steady blowing however
this leads to a drag increase, possibly due to the formation of longitudinal vortices. This
indicates that future methods must include vortex control in conjunction with separation control
to achieve a net base pressure increase on the high angle slant configurations.