Budgets of Turbulent Kinetic Energy and Reynolds Normal Stresses in Coaxial Jets with and Without Swirl: A Numerical Study

Abstract

The influence of swirl on the budgets of turbulent kinetic energy and Reynolds normal stresses is investigated for the configuration of coaxial jets by using direct numerical simulation (DNS) method. A case of strong swirl is studied and compared with a non-swirling case. As the consequence of strong swirl, a vortex breakdown bubble (VBB) is formed. Budget analysis of turbulent kinetic energy (TKE) shows that the higher energy produced at shear layers of upstream region of central stagnation point as the consequence of swirl is transported to the outer jet central region through turbulent diffusion. Moreover, TKE in outside region of VBB is convected from highly energetic upstream region to the downstream region in swirling case, whereas the positive contribution by convection term in nonswirling case seems to be smaller. Budget analysis of the Reynolds normal stresses in upstream region of central stagnation point uncovers that the pressure-strain correlation term acts as energy sink for radial component of Reynolds normal stress at outer shear layer in the swirling case contrary to non-swirling case. In swirling case, a distinctive negative production of the radial component of Reynolds normal stress is observed upstream of central stagnation point in the inner shear layer.