Direct numerical simulation of vector-controlled free jets

Abstract

We conduct DNS (direct numerical simulation) of vector controlled free jets. The inflow velocity of jet is periodically oscillated perpendicular to the jet axis. In order to realize the high accurate computation, a discretization in space is performed with hybrid scheme in which Fourier spectral and 6th order compact scheme are adopted. From visualized instantaneous vortex structures, it is found that the flow pattern considerably changes according to the oscillating frequency, i.e., according to the increasing the frequency, wave, bifurcating and flapping modes appear in turn. In order to quantify mixing efficiency under the vector control, as the mixing measure, statistical entropy is investigated. Compared to the uncontrolled jet, the mixing efficiency is improved in order of wavy, flapping and bifurcating modes. Thus the vector control can be expected for the improvement of mixing efficiency. Further to make clear the reason for the mixing enhancement, Snapshot POD and DMD method are applied. The primary flow structures under the vector control are demonstrated.