Flow Performance Enhancement of a Fluidic Oscillator Through the Integration of Rectangular Ribs on Coanda Surface

Abstract

Fluidic oscillators utilize internal flow dynamics to produce oscillatory fluid jets. The Coanda surface in the mixing chamber of a fluidic oscillator plays a critical role by facilitating controlled fluid manipulation through flow attachment and redirection. The mixing chamber pressure drop, jet oscillating frequency, and deflection angles are hence dependent on the geometry of the Coanda surface. In this study, the Coanda surface is modified by using rectangular ribs of different aspect ratios. The effects of ribbed Coanda surface on oscillating jet characteristics are computed numerically through two-dimensional unsteady Favre-averaged Navier–Stokes equations. The aspect ratio (ARribs), the ratio of rib height to rib base, is varied from 0.64 to 1.56 and air is used as a working fluid. An increase in the ARribs increases the jet oscillation frequency. The highest aspect ratio achieves an oscillation frequency of 820 Hz, contrasting with 355 Hz for the smooth case. On the other hand, the jet deflection angles are decreased as the aspect ratio increases. Interestingly the introduction of the ribs on the Coanda surface decreased the pressure drop in the oscillator. A decrease in pressure drop of 22% for an aspect ratio of 1.56 was achieved as compared to the smooth case. These results are attributed to the influence of the ribs on the formation of a separation bubble formed in the mixing chamber. The jet performance parameter, frequency-deflection-pressure ratio, was found to be 43% higher for ARribs of 1.56 as compared to the smooth case.