Optimization of Synthetic Jet Actuator design for noise reduction and velocity enhancement

Abstract

In this paper the effect of lobed orifice geometry on the self-noise generated by synthetic jet actuators (SJA) is investigated. Two different lobed orifices were designed, one 4-lobed and one 6-lobed. These were then compared to a baseline circular orifice with the aid of CFD simulations, where all orifices have the same effective diameter, de = 2mm. It was shown that the 6-lobed orifice would be the most suitable orifice for the task of noise reduction, as the increased turbulent kinetic energy due to increased mixing occurs further away from the jet core and would enhance mixing without aggressively impacting the jet core velocity. The 6-lobed orifice was then experimentally validated. An analysis of the jet velocity profile at several downstream locations from the orifice exit indicates that though the exit velocities are the same in both orifice cases there is increased mixing causing the jet core to dissipate at a faster rate downstream compared to the baseline circular orifice. Also a noise spectrum analysis shows that there is a broadband noise reduction using the 6-lobed orifice over mid to high frequency range. NomenclatureA = Orifice area, m 2 a = Speed of sound, m/s D = Cavity diameter, mm d = Orifice diameter, mm de = Effective orifice diameter, mm rD = Orifice radius, m = density, kg/m 3 H = Cavity height, mm h = Orifice height, mm f = Actuation frequency, Hz fh = Helmholtz resonance frequency, Hz fd = Diaphragm resonance frequency, Hz E = Young's Modulus, Pa td = Diaphragm thickness, mm = Empirically obtained damping coefficient k 2 = dimensionless frequency parameter = Diaphragm Poisson's ration = Kinematic viscosity of air, m 2 /s 1 PhD Student, College of Engineering, Design and Physical Sciences, UB8 3PH

Experimental investigation of the aeroacoustics of synthetic jet actuators in quiescent conditions

“…Peak velocity performance of a SJA is achieved by operating the device at the synthetic jet resonant frequency, which closely coincides with the mechanical resonance frequency. However, due to the inherent "noisy" acoustic spectrum of commercial piezoceramic diaphragms associated with the presence of several harmonic frequencies of the actuation frequency, fa, it is difficult to distinguish jet noise from the diaphragm noise [13]. For this reason, electromagnetic actuation with a latex membrane for the SJA diaphragm was chosen to study the effect of jet noise without the excessive influence of diaphragm noise in the acoustic data ( Fig.…”