Active control of axisymmetric jet with an array of micro electro-magnetic flap actuators

Abstract

A novel axisymmetric jet nozzle equipped with a row of miniature electromagnetic flap actuators on its circular lip is developed for active flow control. Each of the flaps fabricated by photolithography is independently driven according to a control signal supplied by a PC. The spatio-temporal flow structures of the controlled jet are studied through flow visualization and quantitative velocity measurements. It is found that artificial disturbances generated by the flaps can modify the formation and evolution of large-scale vortical structures significantly. When each half cluster of the 18 flaps are driven out of phase, the jet bifurcates clearly into two branches owing to the interaction between alternatively inclined vortex rings. The optimum Strouhal number, at which the centerline velocity drops to about 45% of that of natural jet, is found to be 0.25 at the jet Reynolds number up to 13 000. A physical model for the bifurcating jet is proposed based on the flow visualization and the phase- averaged velocity and vorticity fields measured by two-dimensional particle tracking velocimetry.