3-D SIMULATION OF TURBULENT THERMALS USING LARGE EDDY SIMULATION

Abstract

A three-dimensional Large Eddy Simulation (LES) model investigating the motion of turbulent axisymmetrical as well as line thermals is presented. The model governing equations arespatially filtered 3-dimensional Navier-Stokes equations and Mass Transport equation. Space derivatives are calculated by Compact Finite Difference Scheme (CFDS) and time derivatives are calculated using Crank-Nicholson method. The turbulence generated is taken care of by eddy viscosity calculated using the modified Smagorinsky model, which includes buoyancy term. The comparison of simulated thermal characteristics like shape, size, buoyancy and mass center velocity for axisymmetrical as well as line thermals, with reported experimental results are found in reasonably good agreement. The behavior of thermal with different length to width ratio (ζ) of initial conditions, is also investigated using this model. It is observed that if the value of ζ is morc than 5, the thermal's behavior is closer to a line thermal of infinite length.