Abstract
In order to control the vortical structure in the wake of a sphere, the active flow control technique using acoustic excitation was utilized. The vortical structure in the wake of a sphere is divided into two different types. One is the alternative vortical structures such as the Karman vortex street. The other is the helical vortices. In the natural condition, one structure becomes superior, but those structures coexist. Therefore, these structures are unsteady. We attempted to control these structures with the acoustic excitation. The structures depended on not only the frequency, but also the acoustic mode. The results showed the acoustic fields influence on the wake structures. Then the acoustic excitation seems to be effective for the flow control with small energy
