Numerical investigation of synthetic jets generated by various signals in quiescent ambient

Synthetic jets generated by four typical and two novel exciting signals are simulated in the present study. The vortex structures and velocity characteristics are analyzed in detail to evaluate the performance of the exciting signal. The synthetic jets excited with the four typical signals, i.e., the triangle signal, sinusoidal signal, trapezoid signal and square signal, are simulated in the first place. It is found that stronger synthetic jets and higher entrainment can be realized by signals with higher peak velocity. Among the typical signals, the most satisfactory performance is observed in the case with the triangle signal. Two novel signals, i.e., the bi-frequency signal and signal with varying duty cycle are subsequently simulated. The numerical result shows that, even with the same peak velocity, the two novel signals have better performance than the triangle signal. The optimal result is achieved in the case with the varying signal. The signal momentum is investigated to fundamentally explain the mechanism behind the different performance of the synthetic jets generated with different signals with the same characteristic velocity. A new parameter, i.e., characteristic momentum is subsequently proposed. The synthetic jets generated with the signals of higher characteristic momentum are found to manifest better performance under the condition of the same frequency and characteristic velocity.