Internal Geometry and External Wall Effects on Fluidic Oscillator Behavior

Abstract

This study quantified the correlation of internal geometry (including Coanda effects) and external walls on oscillation frequency for a fluidic oscillator that was tested for a variety of mass flow rates using CO2 gas. The oscillator designs were modified by altering the aspect ratio (AR) with respect to the exit nozzle and changing the cross-sectional area ratio (MR) between the exit throat and power nozzle. The AR and cross-sectional MR were shown to be correlated with frequency. External walls parallel to each other and perpendicular to the oscillator exit throat were added at varying separation distances to observe how they affected the jet oscillation angle and frequency. By increasing the convexity of the exit throat, Coanda effects were about three times more effective in increasing the oscillation angle compared to wall effects. The internal geometry effects were combined by nondimensional analysis to find a function for predicting the frequency of an oscillator in terms of aspect and area ratios. The function showed that the oscillators converged to a single Strouhal number of 0.016.