Large eddy simulation of turbulent flow and mass transfer in far-field of swirl diffusers

Herein, the turbulent flow structures, mass transfer and ventilations characteristics in the far-field of swirl diffusers are numerically studied at different swirl angles (45° ≤ α ≤ 65°). The results are obtained via a 2nd order finite difference scheme and large eddy simulation (LES) with the dynamic Smagorinsky procedure in sub-grid-scale modeling. Accordingly, the instantaneous and average velocity distributions, transient evolution of the mass transfer, and the overall and local air qualities are investigated in this paper. Also, three main secondary-flow structures are observed in the simulations: a bubble vortex breakdown (α ≤ 45°), a toroidal recirculation zone on the top corners of the room (α ≤ 50°), and a toroidal central recirculation zone attached to the floor (far-field). However, the jet type alternates from the open swirl to Coanda jet in the range 50° ≤ α ≤ 55°, where both types exhibit enhanced ventilation characteristics. In this range, the open swirl jet with the highest swirl angle is more effective in discharging the aged air and also shows improved local air quality in the central region of the room (at α = 50°). On the other hand, the Coanda jet with the least swirl angle is more effective in mixing the fresh air throughout the domain and improves the average air quality (at α = 55°).