Evaluation of LES sub-grid scale models and time discretization schemes for prediction of convection effect in a buoyant pool fire

Abstract

The identification of the type of regime has an essential effect on the selection of sub-grid scale and discretization methods, regarding the accuracy and computational time. In order to investigate the role of sub-grid scale and time discretization method in a pool fire modeling by the Large Eddy Simulation (LES), three sub-grid scales Smagorinsky, one-equation and Wall-Adapting Local Eddy-Viscosity (WALE) and three time discretization methods of first-order Euler method, second-order Crank Nicolson and backward second-order were investigated. The results indicate that WALE and one-equation sub-grid scale have an acceptable prediction, while Smagorinsky has a significant error with the experimental results. Different time discretization methods have little effects on the results of mean velocity and mean turbulent parameters of the pool fire. By considering the instantaneous distribution of parameters, all three methods perform similar results where the kinetic energy is less than 5 m 2 /s 2 . In areas where the perturbation is aggravated, the two second-order discretization methods have the same error with a little difference by the first-order Euler method. The accuracies of second-order methods are about 10% for the velocity prediction, compared to the experimental results, while the error of the Euler method is 15%.

Large eddy simulations fire modeling of JIS A 1310 façade calibration test with respect to sidewall

“…In LES modeling, parameters are obtained in two parts: the directly solved component and the sub‐grid scale (SGS) modeled component, with the filter Δ determined by the mesh size. Among the SGS models, both wall‐adapting local eddy‐viscosity (WALE) and one‐equation eddy viscosity model have demonstrated satisfactory accuracy in fire simulations 24 . The merit of WALE 25 in predicting turbulence behavior requires an extremely fine near‐wall mesh resolution, based on this consideration, the one‐equation eddy viscosity model is adopted.…”

“…Among the SGS models, both wall-adapting local eddy-viscosity (WALE) and one-equation eddy viscosity model have demonstrated satisfactory accuracy in fire simulations. 24 The merit of WALE 25 4 is defined as the dissipation rate, 26 where k sgs is the SGS kinetic energy, D ij is the strain rate tensor, and τ sgs represents the stress tensor; C ϵ and C k are model coefficients with C ϵ = 1.048, C k = 0.03.…”