Adjustable Frequency Fluidic Oscillator with Supermode Frequency

Abstract

This Paper introduces a feedback-type fluidic oscillator design with adjustable frequency at a constant flow rate. Details of the internal and external flowfields were revealed by numerical simulations with the help of frequency measurements and visualizations. Fluidic oscillator’s internal flowfield was manipulated by fluid injection from the islands of the oscillator into the interaction chamber. The interaction between the oscillator’s main jet and the control jets was observed to generate vortices in the mixing shear layers of the jets due to the Kelvin–Helmholtz instabilities. These vortices started to govern the separation bubble characteristics as the control flow rate was increased. After a certain control flow rate threshold was exceeded, the oscillations were no longer controlled by the feedback flow. Instead they were controlled by the vortices generated by the instabilities, resulting in much higher frequencies. These high-frequency oscillations in the supermode control flow rates were determined to be as high as five times the regular frequency of the oscillator. However, a reverse relationship between frequency and sweep angle was also identified. Depending on the amount of control flow at a constant total flow rate, three regions and five cases distributed in these regions are reported.