Interaction between fluidic oscillator and backward-facing step flow by numerical simulation and dynamic mode decomposition analysis

In this paper, we use numerical simulation and dynamic mode decomposition (DMD) to simulate and analyze the coupling characteristics between self-excited sweeping jet and backward-facing step separated flow. The sweeping frequency of the fluidic oscillator is largely influenced by the external separated flow, thus changing its own frequency to the dominant frequency of the separated flow or its multiples. The flow loss is minor when the overall flow frequency is the dominant frequency of the separated flow or its multiples. Moreover, the fluidic oscillator velocity should not be too high to produce excessive unsteady disturbance to the freestream and increase the flow losses. When the inlet flow velocity is 65 m/s and the jet velocity of the fluidic oscillator is 40 m/s, the total pressure loss coefficient of the backward-facing step is reduced by approximately 4.7%. According to DMD analysis, the effective fluidic oscillator control can simplify the frequency mode and decrease its vortical motion loss. Combined with the streamwise amplification effect of the flow instability of the separated flow on the dominant DMD mode, the flow field is locked to some multiple of the dominant frequency of the uncontrolled flow field through the coupling effect of the fluidic oscillator and the separated flow.