Control of wake dynamics in a narrow gap by a sweeping jet

An experimental study of the active control of wake flow in a narrow gap using a sweeping jet generated by a fluidic oscillator was conducted using planar laser-induced fluorescence and time-resolved particle image velocimetry. Spectral proper orthogonal decomposition of the velocity fields shows that the flow dynamics in the narrow gap, controlled by the sweeping jet, depends on the ratio of the jet oscillation frequency to the natural frequency of the Karman vortex street in the narrow gap. An increase in the jet oscillation frequency above the natural frequency causes the flow to reorganize into bimodal shedding of vortex structures—two Karman vortex streets with distinct wavelengths—within the narrow gap, which transition downstream to a unimodal flow regime at frequencies near the natural one. This extends the range of controllable spatiotemporal scales and enhances mixing efficiency. The results of this work are significant for the development of methods for detecting flow blockages in high-power equipment of nuclear power plants.