Hybrid LES/URANS Simulation of Rayleigh-Bénard Convection Using BEM

In this paper,we develop and test a unified hybrid LES/URANS turbulence model with two different Large Eddy Simulation(LES)turbulence models.The numerical algorithm is based on the Boundary Element Method.In the existing hybrid LES/URANS turbulence model we implemented a new Smagorinsky LES turbulence model.The hybrid LES/URANS turbulence model is unified,which means that the LES/URANS interface is changed dynamically during simulation using a physical quantity.In order to define the interface between LES and unsteady Reynolds Averaged Navier Stokes(URANS)zones during the simulation,we use the Reynolds number based on turbulent kinetic energy as a switching criterion.This means that the flow characteristics define where the sub-grid scale or URANS effective viscosity and thermal conductivity are used in the governing equations in the next time step.In unified hybrid turbulence models,only one set of governing equations is used for LES and URANS regions.The developed hybrid LES/URANS model was tested on non-isothermal,unsteady and turbulent Rayleigh-Bénard Convection and compared with an existing model,where LES is based on turbulent kinetic energy.The hybrid turbulence model was implemented within a numerical algorithm based on the Boundary-Domain Integral Method,where a single domain and sub-domain approaches were used.The numerical algorithm uses governing equations written in a velocity-vorticity form.The false transient time scheme is used for the kinematics equation.