Study of the transient flow structures generated by a pulsed nanosecond plasma actuator on a delta wing

The transient flow structures produced by a pulsed nanosecond plasma actuator and the mechanism by which they are generated are investigated experimentally and through simulations for the case of flow control on a non-slender delta wing. Phase-locked particle image velocimetry reveals a phenomenon in which, after each discharge pulse, two sub-vortices are generated in sequence and move along the shear layer regardless of the angle of attack, and this is confirmed by hot-wire anemometry. However, at high actuation frequencies ( F+ = fc/ U∞ {greater than or equal to} 6.435), this phenomenon of double sub-vortices is not observed, and only one sub-vortex is generated per period. The results of pressure measurements indicate that each sub-vortex gives rise to a distinct pressure fluctuation on the wing surface. Numerical simulations reveal a number of residual heats resulting from plasma thermal effects in the shear layer, each of which turns out to induce a corresponding sub-vortex. At low actuation frequencies ( F+ {less than or equal to} 4.29), there is a division of the initial residual heat into two independent residual heats and hence double sub-vortices per period, whereas at high actuation frequencies ( F+ {greater than or equal to} 6.435), residual heats from two consecutive periods merge into one, resulting in just one sub-vortex per period, which provides an explanation for the experimentally observed flow behavior.