Interaction of synthetic jet propulsion with airfoil aerodynamics at low Reynolds numbers

The use of synthetic (zero net mass flux) jets for the propulsion of fixed-wing small unmanned air vehicles was investigated. The formation of a time-averaged jet resulting from periodic excitation of a cavity and its interaction with separated flow over the airfoil were studied. As a thick trailing edge does not have an adverse effect on lift generation at low Reynolds numbers, a synthetic jet was placed at the trailing edge of the airfoil. It was shown that when the synthetic jet is activated the separated shear layer reattaches near the trailing edge of a cambered airfoil for momentum coefficients larger than a critical value, resulting in enhanced lift. For momentum coefficients larger than a critical value, the jet produces positive thrust, which strongly depends on excitation frequency. An optimum frequency range was identified, which produces maximum thrust. Aerodynamic efficiency was investigated as a function of the main parameters.