Piezo-driven and Plasma Synthetic Jet Actuators. A comparative investigation

The active flow control is one of the most effective methods to improve the aircraft performances. This technique involves electro-mechanical devices, such as synthetic jets actuators, able to manipulate the flow,modify its structure and allow a suited variation of the aerodynamic forces on the aircraft. Both piezo-driven and plasma synthetic jet actuators (SJA) have gained much interest for their simplicity, very short response time, high jet velocity and lack of anymoving parts. Inthe former case a synthetic jet is generated by the diaphragm oscillation (driven by a piezoelectric element) in a relatively small cavity, producing periodic cavity pressure variations associated with volume changes. The pressured air exhausts through an orifice, converting electrodynamic energy into jet kinetic energy. On the other hand, a plasma SJA is essentially composed of 2 or 3 electrodes embedded in a small cavity linked to the external environment through an orifice. An electrical discharge sharply increases pressure and temperature inside the cavity. The high-pressure air exhausts through the orifice, converting the increased air internal energy into kinetic one. In both the cases, the device rapidly reaches a periodic behavior, generating a so-called synthetic jet. This paper aims at representing a review of both the techniques, outling their major peculiarities in terms of jet velocity and energy efficiency. Various Lumped- Element Models (LEMs), as practical tools to design and manufacture the actuators, are discussed as well.