Experimental Study of Aerodynamic Drag Control on Bluff Body using Synthetic Jets

Since flow separation causes increase of the drag on bluff bodies, its control method has been studied for many years. Active control methods are currently focused as an alternative to passive ones because they impose a larger drag penalty under certain conditions. Although the effectiveness of a steady jet using suction, blowing or pulsed jets has been demonstrated, it is difficult to obtain an effect commensurate with weight increase because the mechanism is complicated.

One method of solving this problem is a synthetic jet. Synthetic jets are produced by periodic ejection and suction of fluid from an orifice induced by oscillation of a diaphragm inside a cavity. Small engine powered vehicles demand less drag, a compact package and light weight because the drivers expect fuel efficiency, load capacity and economy. Synthetic jets can supply them because they contribute drag reduction and require only simple components.

In this study, the influence of synthetic jets on the drag of a simple bluff body representing a road vehicle is measured. Drag measurement was performed by varying synthetic jet parameters: jet location, reduced frequency, velocity ratio of jet flow and uniform flow. The vortex structure around the body was visualized by utilizing a smoke wire method. As a result, among the jet parameters, only reduced frequency had no effect on drag.