On the application of confined twin-jet instability to micro-mixing enhancement

The confined twin-jet hydrodynamic instability is exploited to enhance mixing of low Reynolds number laminar flows. The baseline flow is investigated numerically and experimentally for three configurations, differing by the jet spacing and wall confinement. Using hot-wire anemometry and particle image velocimetry, the Reynolds and Strouhal numbers associated with flow bifurcations were detected and are in good agreement with current and previously published numerical simulations. Superimposing weak harmonic excitation on the baseline twin-jets flow is shown to significantly enhance the naturally unstable modes, and to generate considerable perturbations at the jets merging area. The influence of excitation frequency and amplitude on the resulting unsteadiness is also studied. It is found that applying excitation with the same Strouhal number to subcritical Reynolds number flow creates similar perturbation structures as for supercritical Reynolds number flows. These findings demonstrate the potential of the confined twin-jet geometry to be utilized to enhance mixing for a wide range of applications where turbulent mixing is absent.