ACTIVE CONTROL OF AN AXISYMMETRIC JET WITH AN INTELLIGENT NOZZLE

An intelligent nozzle equipped with a row of miniature flap actuators on its exit lip is developed for active flow control. The spatio-temporal structures of the controlled jet are studied through two-dimensional velocity field measurement. When each half cluster of flaps are driven out of phase, the jet clearly bifurcates into two branches. The detailed bifurcating mechanism is explored by examining phase-averaged velocity and vorticity fields. It is found that the vortex ring, which is alternatively inclined due to the difference of induced velocities between the upper and lower halves, causes the stable slip-through motion with the preceding half of vortex ring. This interaction makes each half of vortex ring turn away from the jet axis. These strongly inclined vortex rings vectorize the jet core fluid alternatively, and thus results in the bifurcating jet.