Fundamental Properties of Fluidic Oscillators for Flow Control Applications

The presented work provides a technical summary of the fundamental time-resolved properties of a spatially oscillating jet emitted by a fluidic oscillator. The discussion focuses on experiments involving a fluidic oscillator with two feedback channels. Although limited to the fundamental properties, the discussions throughout the paper are frequently directed at the use of fluidic oscillators for flow control applications, which is accompanied by numerous suggestions for future research activities. The internal flow field reveals the oscillation mechanism that is based on flow guided through the feedback channels to feed into a recirculation bubble. The bubble grows and pushes the jet to the opposite side. Scaling parameters are introduced that govern the oscillation frequency for different oscillator sizes and working fluids. The external flow field within a quiescent environment visualizes the jet’s sweeping motion. A head vortex is formed repetitively. The jet’s properties (e.g., jet velocity, jet depth, and entrainment) change throughout one oscillation cycle. The jet velocity decays much more rapidly than for a steady jet, which is accompanied by a significant increase in jet depth. These observations are consistent with the finding that the jet entrainment is at least four times higher than for a steady jet. Furthermore, the jet forces are assessed from the flow field data. When a single oscillating jet interacts with a crossflow over a flat plate, pockets of streamwise vorticity are formed and convected downstream. Depending on Strouhal number, the streamwise vortices alternate gradually or in an almost bi-modal manner.