General Reduced-Order Model to Design and Operate Synthetic Jet Actuators

Abstract

Synthetic jets are used in various applicat ions from flow contro l to thermal management of electronics. Controlling the jet operating point using a simple voltage to velocity calibration becomes unreliable in case of ext ernal pressure field disturbances or varying actuator characteristics. This paper pres ents a general lumped parameter model for a synthetic jet actuator with electromagnetic or piezoelectric driver. The fluidic model accurately predicts the synthetic jet operati ng point (i.e. Reynolds number and stroke length) based on the measured cavity pre ssure. The model requires only two empirical coefficients characterizing nozzle fluid damping and inertia . These can be obtained via calibration or estimated from pressure loss co rrelations and the governing acoustic radiation impedance. The model has been validated experimentally for a ci rcular and rectangular orifice. The effect of nozzle damping on the nonlinear system response is discussed. Analytical expressions are given for the two resonance frequencies characterizing the system response, as a function of the diaphragm a nd Helmholtz resonance frequencies. The optimal design of an impinging synthe tic jet actuator is discusse d in terms of the thermal and acoustic efficiency. Guidelines for selectin g the optimum combination of diaphragm and Helmholtz resonance frequency are presente d and compared to previous studies.