“…Recent decades have witnessed significant advances in zero and nonzero mass-flux devices including piezoelectric (Chen et al, 2000;Glezer and Amitay, 2002) valve-type (Seifert, Darabi and Wygnanski, 1996;Bachar, 2001;Seifert and Pack, 1999) and pulsed combustion or detonation-driven (Crittenden et al, 2001) devices. The same is true for surface-mounted actuators that include piezoelectric , plasma-based (Sosa et al, 2006;Post and Corke, 2004), arc filament (Samimy et al, 2004), shape memory alloys (Wlezien et al, 1998), and Lorentz force (Weier and Gerbeth, 2004) actuators. Perturbations produced by the actuators may be small relative to a characteristic velocity or vehicle dimension and thus exploit boundary layer instability; but they may also be much larger and hence "force" the flow, for example, by high-frequency alternating blowing and suction.…”