Acoustic analysis of low-noise actuator design for active flow control

This paper presents an acoustic analysis of low noise actuation design concepts for active flow control by pulsed jets. The low noise concepts are based on the principle of phase cancellation of coherent unsteady fluctuations. It is shown that by suitably arranging the actuators with prescribed phase variations, active flow control actuators using pulsed jets can achieve very low levels of near-field unsteady fluctuations and far-field noise, while maintaining the same effectiveness in flow control as those conventional designs without the phase cancellation implementation. To demonstrate the concepts, flow separation control on an airfoil is discussed in detail, and numerical simulations are given to show the flow control effectiveness and the low noise features of the actuation design. Simple analytical models are presented to reveal the characteristics of noise radiation from pulsed jet actuators, which relates the near-field pressure and far-field noise to various parameters such as the mean flow Mach number, the frequency of the pulsed jets and the phase variation algorithm. The explicit analytical results can be used as a quick design guide in practical applications.