Helical Structure Formed in the Initial Region of a Round Jet by Three Synthetic Jets

Abstract

Round jets have symmetric and asymmetric modes, and symmetric mode typically appears near the nozzle. However, by controlling the jet, asymmetric mode, i.e., helical mode, can be formed near the nozzle. Here, a round nozzle has three holes for the synthetic jets. The three holes are positioned at equal intervals around the circumference of the nozzle. By sequentially driving the three synthetic jets, a helical structure is formed near the nozzle exit of the round jet. The frequency of the synthetic jets is set to the frequency of vortex-ring formation in the natural transition. The results of numerical simulation using OpenFOAM and experimental results, such as, flow visualizations and PIV measurements, are presented for this flow field.