Towards a practical piezoceramic diaphragm based synthetic jet actuator for high subsonic applications - effect of chamber and orifice depth on actuator peak velocity

An investigation on the effect of geometry and actuation variables on peak jet velocity of a piezoelectric diaphragm synthetic jet actuator was conducted using hotwire anemometry. Two distinct experiments were conducted; the first at constant excitation amplitude with the aim of identifying the SJA geometry that provides the highest jet velocity. This geometry was then used in a second experiment with constant geometry to explore the effects of excitation amplitude on actuator jet velocity. The results show that the actuator jet velocity is inversely proportional to both the orifice and chamber depth over the range of parameters tested. The actuator parameters that provide the highest peak jet velocity were identified to be H/Do = 0.6 and h/Do = 2.1, where H is the chamber depth, h is the orifice depth and Do is the orifice diameter. Excitation at the mechanical diaphragm resonance frequency resulted in jet velocities double the magnitude of those observed at cavity resonance. The Helmholtz theory consistently over estimated the cavity resonance frequency by ≈ 18%. Peak actuator velocities of around 130m/s from a 1.2mm diameter orifice can now be reliable achieved. The outcome of this investigation is considered to be a positive step on the understanding on how design and actuation parameters influence the performance of a synthetic jet actuator.