The Effect of Spatially and Temporally Modulated Plasma Actuation on Cylinder Wake

The wake of a circular cylinder was forced with a temporally modulated and spatially segmented dielectric-barrier-discharge plasma actuator. The temporal modulation was achieved by modulating the applied voltage signal with a square wave whose frequency was twice the vortex shedding frequency. The spatial segmentation was implemented by locating the buried electrodes only at certain spanwise locations along the cylinder in a square-wave pattern. Two blowing ratios (BRs), namely BR=0.2and 0.6, were implemented. In the case of BR=0.6, vortex shedding was significantly attenuated, and the frequencies of the most prominent peaks in the spectra of velocity fluctuations were considerably different along the span. Moreover, the subharmonic mode was found to be stronger behind the non-plasma-forming region compared to the plasma-forming region during forcing with BR=0.6. It also resulted in less drag compared to the unforced case. In the case of BR=0.2, the unsteadiness and the velocity defect in the wake increased compared to the unforced case. Finally, the performance of the segmented actuator was compared with a straight two-dimensional actuator by maintaining the same induced velocity. In this case, a "W"-shaped velocity profile was obtained during both the low- and high-power forcing. Modulated forcing with the straight actuator increased the drag compared to the unforced case.