Bifurcating flows or helical structures formed in the initial region of a round jet by synthetic jets arranged in a nozzle

A round jet is periodically disturbed by synthetic jets at near the exit of a round nozzle. The synthetic jets are formed from holes arranged circumferentially in the round nozzle, because the holes are connected to loudspeakers inputting a sinusoidal wave through vinyl tubes. The number of holes, namely synthetic jets is 3 to 6. When the synthetic jets are driven in the same phase and at the vortex formation frequency of the natural transition of the jet, bifurcating flows can be formed near the nozzle. The number of bifurcating flows is identical to the number of synthetic jets. Consequently, by driving the synthetic jets in symmetric mode, the mixing between the jet and surroundings is enhanced near the nozzle exit. The experimental results can be numerically simulated using OpenFOAM. Numerical simulations are also shown that helical structures can be formed in the potential core by driving the synthetic jets in sequence, that is, by driving the synthetic jets in a rotational manner. In this case, the mixing near the nozzle outlet is suppressed. In addition, when six synthetic jets are used, a double helix structure can be formed by driving them with a phase difference, so that the jet breaks down further downstream. This means that mixing of the jet is further suppressed in this case.