Matteo Chiatto

LEM Characterization of Synthetic Jet Actuators Driven by Piezoelectric Element: A Review

In the last decades, Synthetic jet actuators have gained much interest among the flow control techniques due to their short response time, high jet velocity and absence of traditional piping, which matches the requirements of reduced size and low weight. A synthetic jet is generated by the diaphragm oscillation (generally driven by a piezoelectric element) in a relatively small cavity, producing periodic cavity pressure variations associated with cavity volume changes. The pressured air exhausts through an orifice, converting diaphragm electrodynamic energy into jet kinetic energy. This review paper considers the development of various Lumped-Element Models (LEMs) as practical tools to design and manufacture the actuators. LEMs can quickly predict device performances such as the frequency response in terms of diaphragm displacement, cavity pressure and jet velocity, as well as the efficiency of energy conversion of input Joule power into useful kinetic power of air jet. The actuator performance is also analyzed by varying typical geometric parameters such as cavity height and orifice diameter and length, through a suited dimensionless form of the governing equations. A comprehensive and detailed physical modeling aimed to evaluate the device efficiency is introduced, shedding light on the different stages involved in the process. Overall, the influence of the coupling degree of the two oscillators, the diaphragm and the Helmholtz frequency, on the device performance is discussed throughout the paper.

Water Spray Flow Characteristics Under Synthetic Jet Driven By a Piezoelectric Actuator

Particle Image Velocimetry (PIV) and Phase Doppler Anemometry (PDA) have been applied to investigate the droplets size and velocity distribution of a water spray, under the control of a piezo-element driven synthetic jet (SJ). Tests were carried out under atmospheric conditions within a chamber test rig equipped with optical accesses at two injection pressures, namely 5 and 10 MPa, exploring the variation of the main spray parameters caused by the synthetic jet perturbations. The SJ orifice has been placed at 45° with respect to the water spray axis; the nozzle body has been moved on its own axis and three different nozzle quotes were tested. PIV measurements have been averaged on 300 trials whereas about 105 samples have been acquired for the PDA tests. For each operative condition, the influence region of the SJ device on the spray has been computed through a T-Test algorithm. The synthetic jet locally interacts with the spray, energizing the region downstream the impact. The effect of the actuator decreases at higher injection pressures and moving the impact region upwards. Droplets coalescence can be detected along the synthetic jet axis, while no significant variations are observed along a direction orthogonal to it.

Feasibility studies for the installation of Plasma Synthetic Jet Actuators on the skin of a morphing wing flap

A morphing structure can be considered as the result of the synergic integration of three main systems: the structural system, based on reliable kinematic mechanisms or on compliant elements enabling the shape modification, the actuation and control systems, characterized by embedded electromechanical actuators and robust control strategies, and the sensing system, usually involving a network of sensors distributed along the structure to monitor its state parameters. Technologies with ever increasing maturity level are adopted to assure the consolidation of products in line with the aeronautical industry standards and fully compliant with the applicable airworthiness requirements. In the framework of the CleanSky2, one of the largest research projects ever funded by the European Union, a novel multi-modal camber morphing flap was conceived for the enhancement of the aerodynamic performances of the next generation green regional aircraft. Thanks to different morphing modes, the shape of the flap can be suitably adapted in order to preserve an optimal configuration as the aircraft trim parameters change according to the specific flight phase (take-off, climb, cruise, descent, landing). To further improve the benefits brought by such technology on the wing aerodynamic efficiency, an active flow control system based on plasma synthetic jet (PSJ) actuators was investigated for a potential installation on the upper skin of the flap. PSJ actuators, or Sparkjets, are able to produce very high jet velocities, without the aid of any moving parts, affecting the structure of the flow-field to be controlled and allowing a positive variation of the aerodynamic forces on the aircraft, with a modest power consumption. This work is focused on the two main aspects related to the feasibility of PSJ actuators integration into the adaptive flap skin: the thermal and electromagnetic interferences of the actuators with the other electronic equipment of the flap. Experimental measurements were carried out to characterize the thermal and the electromagnetic fields induced by the operating device into the surrounding structure. A simplified test article was designed and manufactured to support all experimental activities while being fairly representative of the actual PSJ-skin assembly. Test results allowed for a definition of the safety-critical areas for the installation of flap actuation, control and sensing systems.