Novel Operating Mode of a Fluidic Oscillator

Abstract

Fluidic oscillators show promise for use in aerodynamic flow control applications, with many studies reporting oscillation frequencies in the 1–10 kHz range. Spyropoulos, “A Sonic Oscillator,” introduced a “sonic” oscillator whose oscillation frequency depends on the inlet flow rate. The purpose of this paper is to demonstrate the existence of a second mode of operation (mode II) for such an oscillator, with a separate physical mechanism to the traditional, flow rate-dependent mode (mode I). Mode II is shown to be a back-pressure-driven oscillation that is largely independent of flow rate once instigated. This is explained by a stationary wave formed along the outlet paths, and occurs when conditions on the degree of back pressure and the weakening of the Coandă attachment strength are met. For a fixed device geometry, the conditions reduce to a minimum flow rate threshold so that the combination of high flow rate and constant oscillation frequency could make mode II an attractive flow control solution in an industrial context where minimizing device size is often critical.