Numerical investigation of efficient synthetic jets generated by multiple-frequency actuating signals

The synthetic jets generated by multiple-frequency actuating signals composed of a basic sinusoidal wave and a superposed high-frequency signal is investigated by two-dimensional simulation in the present study. The effect of the frequency and amplitude of the high-frequency signal on the synthetic jet in the quiescent flow is investigated in detail with stroke length ratio L and Reynolds number Re-U0 kept as constant. It is found that, with the high-frequency signal superposed, the vortex pairs induced by the synthetic jets are strengthened and accelerated. The distance that the vortex pairs can propagate downstream is also elongated. The entrainment of the synthetic jets is thus enhanced as well. The optimal design is reached when the frequency ratio, defined as the ratio between the superposed signal frequency and the basic signal frequency, is fixed at f(+) = 2. At this optimal frequency ratio, the jet entrainment increases monotonously with the amplitude of the high-frequency signal.