Additive manufacturing impact on a fluidic oscillator with respect to surface roughness

Abstract

This experiment investigates the impact of areal surface roughness Sa on the performance of a fluidic oscillator produced by additive manufacturing (AM) versus the conventionally machined samples. The fluidic oscillator used is a classical curved (Type-II) Sweeping Jet (SWJ) actuator with two feedback channels. The interior surface finish of each sample is characterized using an optical 3D measurement system. The performance of the emanated jet is evaluated using hot-wire anemometry downstream of the outlet nozzle while the required supply pressure is recorded using a high-frequency pressure transducer at the actuator inlet. A bifurcated velocity profile of the external flow typical for the SWJ is observed in all cases, irrespective of the manufacturing process and surface roughness Sa< 20 μm. The jet velocity profiles are found to be satisfactorily self-similar, confirming that the surface roughness in the examined range does not qualitatively change the internal flow dynamics. However, increasing the surface roughness causes a reduction in the output jet spreading and a concomitant increase in the jet oscillation frequency. A linear model is presented to estimate the jet spreading versus the surface roughness.