Flow Mechanism of a Self-Induced Oscillating Jet Issued from a Flip-Flop Jet Nozzle

Abstract Flow and pressure in a short diffuser placed at exit of a plane turbulent jet have been studied. With connecting two ports in the diffuser by a duct, jet direction oscillates laterally. Flow pattern in the diffuser is visualized by smoke and instantaneous velocities and pressures are measured by using hot-wire anemometers and semiconductor pressure transducers. Phased-locked ensemble averages of velocity and pressure are deduced to examine the detailed nature of the oscillatory flow. These measurements reveal that the jet attaches alternatively on both walls of the diffuser with keeping two-dimensionality. The detaching speed is much slower than the attaching one. The jet oscillation accompanies the vibration of port pressures and duct flow. By examining the results with fluid dynamics, it is clarified that the jet is bent by port pressure difference via lateral momentum equation without unsteady effect and the duct flow is driven by port pressure difference via unsteady duct flow equation. A flow model to govern the port pressure change is proposed, that is, the pressure is determined by the balance between jet entrainments and air supply. By combining these relationships, a closed feedback model of the oscillation is provided to explain flow mechanism of the oscillation