Verification and validation of a variable–density solver for fire safety applications

Abstract An iterative variable–density solver is developed and implemented in Code_Saturne, a finite-volume code. The method of manufactured solutions (MMS) is used to investigate the convergence and the order of accuracy of the algorithm. A well-documented large-scale helium buoyant plume is simulated by large-eddy simulation (LES) to validate the code against experimental data. MMS verification confirms the second-order accuracy of the code. LES of helium plumes are performed by using the dynamic Smagorinsky model for subgrid-scale (SGS) stress tensor and five dynamic SGS scalar flux models including, the classical dynamic eddy diffusivity model (DEDM), two models based on the generalized gradient diffusion assumption, and two other mixed models based on the Taylor series expansion. Predictions obtained with the DEDM provide on the whole a good agreement with the experimental data although the mixing rate at vicinity of the plume centerline is underestimated. The other SGS scalar flux models reduce these discrepancies, especially close to the plume source. In addition, helium mass fraction and its fluctuation are more sensitive to grid refinement than SGS scalar closures which suggest that the small-scale buoyancy effects are not fully captured by the present LES. The validated LES code provides state-of-the-art predictions as compared to other numerical studies and can be applied to fire safety applications in the future.