Oscillation behaviors of planar opposed jets with acoustic excitation were experimentally investigated. The flow regimes of planar opposed jets at various exit air velocities, nozzle separations, excitation frequencies, and excitation amplitudes have been identified by a flow visualization technique combining with a high-speed camera. Results show that planar opposed jets exhibit horizontal instability at L/H ≤ 4 (where L is the nozzle separation and H is the slit height of the planar nozzle) and deflecting oscillation at L/H ≥ 6. The deflecting oscillation is originally started by the antisymmetric structures in the planar jets and is self-sustained by the periodic changes of the velocity field and the pressure field. At L/H ≤ 4, the acoustic excitation results in the horizontal periodic oscillation, whose frequency is equal to the excitation frequency. The acoustic excitation of oscillation amplitude less than 10% has negligible influence on the deflecting oscillation; for synchronous or asynchronous excitation with higher amplitude, the transition from the deflecting oscillation to a steady state or horizontal oscillation occurs.

Oscillation behaviors of axisymmetric opposed jets with modulated airflow were experimentally studied. The oscillation frequency, the oscillation amplitude, and the movement velocity of the impingement plane at various nozzle separations, excitation frequencies, and exit turbulence intensities have been investigated by a hot-wire anemometer and flow visualization technique combined with a high-speed camera. Results show that the oscillation frequency of the impingement plane is nearly equal to the excitation frequency, whereas the oscillation amplitude decreases with the increase of the excitation frequency. The full-scale amplitude oscillation occurs at low excitation frequencies and 2 L/D 8 (where L is the nozzle separation and D is the diameter of the nozzle exit). With the increase of the exit turbulence intensity caused by a turbulence generating plate, the oscillation amplitude decreases remarkably. Flow regimes of axisymmetric opposed jets with excitations are analyzed and discussed based on the experimental results.

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