Numerical Investigation on Flow Structures and Mixing Performances of Vector-Controlled Free Jet using DNS

Abstract

In order to develop a new mixing procedure, we conduct DNS (direct numerical simulation) of vector controlled free jets. The inflow velocity of jet is periodically oscillated perpendicular to the jet axis. To realize the high accurate computation, the discretization in space is performed with hybrid scheme in which Fourier spectral and 6th order compact scheme are adopted. From view of 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 like mode, bifurcation mode and flapping mode appear in turn. In contours of ensemble averaged streamwise velocity and turbulence kinetic energy, the jet diffuses largely in the oscillating direction. On the other hand, the jet width in the perpendicular to the oscillating direction is similar to that of uncontrolled jet. Further in order to quantify the mixing efficiency under the vector control, as the mixing measure, the statistical entropy is investigated. Compared to the uncontrolled jet, the mixing efficiency is improved in order of the wave- , the flapping- and the bifurcating mode. Thus the vector control can be expected for the improvement of mixing efficiency.