Abstract
One of the main advantages of fluidic oscillators is that they do not have moving parts, which brings high reliability whenever being used in real applications. To use these devices in real applications, it is necessary to evaluate their performance, since each application requires a particular injected fluid momentum and frequency. In this paper, the performance of a given fluidic oscillator is evaluated at different Reynolds numbers via a 3D-computational fluid dynamics (CFD) analysis. The net momentum applied to the incoming jet is compared with the dynamic maximum stagnation pressure in the mixing chamber, to the dynamic output mass flow, to the dynamic feedback channels mass flow, to the pressure acting to both feedback channels outlets, and to the mixing chamber inlet jet oscillation angle. A perfect correlation between these parameters is obtained, therefore indicating the oscillation is triggered by the pressure momentum term applied to the jet at the feedback channels outlets. The paper proves that the stagnation pressure fluctuations appearing at the mixing chamber inclined walls are responsible for the pressure momentum term acting at the feedback channels outlets. Until now it was thought that the oscillations were driven by the mass flow flowing along the feedback channels, however in this paper it is proved that the oscillations are pressure driven. The peak to peak stagnation pressure fluctuations increase with increasing Reynolds number, and so does the pressure momentum term acting onto the mixing chamber inlet incoming jet.
Highlights
Flow control actuators have traditionally been a research topic in the fluid mechanics field.Their use on bluff bodies allows modifying lift and drag, reducing flow instabilities, as well as the energy required for the body to move
In order to properly understand the flow configuration and the forces acting inside the Fluidic Oscillators (FOs), Figures 5 and 6, which introduce the dimensional values of the oscillator and Feedback Channels (FC) volumetric flows, the Mixing Chamber (MC) inlet, and outlet jet inclination angles, the pressure at different locations inside the MC, and the net momentum acting on the jet at the feedback channels outlet will be linked with Figure 4
In order to properly understand these statements, the following dynamic non-dimensional parameters were compared in Figure 11: the stagnation pressure at the MC lower converging surface, the net momentum acting on the jet, the MC incoming jet oscillation angle, and the FO upper outlet mass flow
Summary
Flow control actuators have traditionally been a research topic in the fluid mechanics field. The curved configuration studied by Aram et al [28] had a larger mixing chamber inlet width than the angled one employed by Bobusch et al [17] and Gokoglu et al [14], which prevented the existence of reversed flow into the feedback channel. The effect of the Reynolds number on the dynamic stagnation pressure and on the pressure momentum term acting on the jet shall further clarify the origin of the oscillations At this point it is very relevant to recall the work done by Wu et al [23], where they applied the curved and angled fluidic oscillator configurations to enhance heat transfer. In the present paper and for a different angled configuration than the ones evaluated by [23], the same conclusion is obtained and is proven fully
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