Impact of scaling and upper/lower wall friction on the behavior of sweeping jet actuators (SJAs)

A series of numerical simulations using the unsteady Reynolds-averaged Navier-Stokes (URANS) method were conducted in the current study to investigate the effects of scaling on the sweeping and frequency characteristics of sweeping jet actuators (SJAs). Three different scales of SJAs, with hydraulic diameters of 1.6, 2.9, and 4.2 mm, respectively, were examined to assess variations in maximum sweeping angle, root-mean square (RMS) values of the transient sweeping angle, and operating frequency under different Reynolds numbers. Additionally, the influence of friction from the upper and lower walls of SJA on its performance was studied by comparing SJAs with different heights (aspect ratio = 1, 0.67, and 0.38) and configurations where the upper and lower walls were set as free slip walls. The results demonstrate that the reduction in SJA scale leads to significant changes in sweeping characteristics, with the maximum sweeping angle decreasing by more than 10° and the normalized RMS value of the sweeping angle distribution also notably decreasing. The frequency characteristics were analyzed by examining the size of the separation bubble in the mixing chamber and the average velocity in the feedback channel, showing variations with scale changes. Additionally, it was found that the friction from the upper and lower walls plays a crucial role in the performance changes observed when the SJA scale is altered. These findings suggest that the impact of performance changes should be carefully considered in the design of SJAs for specific applications, and appropriate adjustments should be made as necessary.