Interaction of dual sweeping impinging jets at different Reynolds numbers

Abstract

Dual sweeping impinging jets emerging from a synchronized pair of fluidic oscillators were experimentally measured using time-resolved particle image velocimetry in a water tank. Interestingly, distinct behaviors of the dual jets were observed at three different Reynolds numbers. At the lowest Reynolds number Re = 1.8 × 103, the dual jets can be generally treated as two isolated jets with a good in-phase sweeping motion and a relatively stable jet velocity. One pair of wall vortices develops and interacts in a trade-off manner in the middle region between the two jets. In the time-averaged flow fields close to the wall, each jet generates one major peak value of streamwise velocity and one pair of peak values (positive and negative) of transverse velocity laterally along the wall. The turbulence fluctuations in both directions also have peak values laterally. In the transverse direction, the velocity also has high turbulence fluctuations in the middle region between the two jets caused by the wall vortices. At the highest Reynolds number Re = 9.2 × 103, the dual jets experience significantly distorted oscillation patterns and strong variations in their jet velocity during one actuation cycle. The dynamic behavior, the induced wall vortices, and the resulting time-averaged impingement of the dual jets are, in essence, very similar to the sweeping jet that would be produced from a single, but bigger, oscillator. At the intermediate Reynolds number Re = 5.5 × 103, the performance of the dual sweeping jets is at the transition stage.