Large-eddy simulations of turbulent flow structures near a quiescent liquid–gas interface for gaseous compounds emissions studies

Abstract

This work aims to study the turbulent flow structures near a gas–liquid interface with negligible surface deformation and its effects on mass transfer of gaseous compounds. Turbulence was modeled using the Large Eddy Simulation (LES) technique with dynamical subgrid scale modeling. The fluids were considered Newtonian, incompressible and isothermal. The mathematical model was validated using Direct Numerical Simulation (DNS) data from literature. Numerical simulations were performed for Reynolds number (based on the friction velocity) equal to 150, 640 and 1280 and Schmidt numbers equal to 1, 200 and 580 allowing for specific investigation of the effects of these governing parameters on the mass transfer phenomenon. Qualitative analysis of surface divergent, instantaneous scalar concentration and fluctuation of scalar concentration showed the existence of turbulent structures influencing on mass transfer near the free surface. The coherent turbulent structures have an almost longitudinal aspect for the lowest Reynolds number investigated, with counter-rotative vortices that act on the formation of vertical upward and downward movements close to the interface. An increase in the Reynolds number is mainly associated with a reduction of the diffusive sublayer thickness due to the increase of scalar concentration mixing in the bulk region. An increase in the Reynolds number also promotes changes in the turbulent structures next to the liquid–gas interface. The mass transfer coefficient in the liquid phase showed a maximum value for Re=1280 and Sc=1.