Direct numerical simulation of dynamic-rotational controlled jet

Abstract

In order to develop a new mixing procedure, we conduct DNS (direct numerical simulation) of dynamic controlled free jets. As the dynamic control, it is assumed that the inflow velocity of jet is alternately rotated around streamwise direction. To realize the high accurate computation, the discretization in space is performed with hybrid scheme in which sine or cosine series and 6th order compact scheme are used. From view of instantaneous vortex structures, it is found that the flow pattern considerably changes according to the rotating frequency, i.e., according to the increasing frequency, helical and entangled mode appear in turn. From the ensemble averaged flow properties such as jet width and entrainment, it is confirmed that the jet widely spreads perpendicular to the rotating axis and that the mixing of upstream jet is markedly enhanced due to the dynamic control. Further in order to quantify the mixing efficiency of the dynamic control, as another mixing measure, a statistical entropy is examined. Compared to the uncontrolled jet, it is confirmed that the mixing efficiency is markedly improved, suggesting that the dynamic control can be expected to be useful for the improvement of mixing performance.