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Evaluation of a Fast, Simplified Computational Fluid Dynamics Model for Solving Room Airflow Problems.


pdf icon Evaluation of a Fast, Simplified Computational Fluid Dynamics Model for Solving Room Airflow Problems. (730 K)
Musser, A.; McGrattan, K. B.; Palmer, J.

NISTIR 6760; 65 p. June 2001.

Keywords:

computational fluid dynamics; air flow; convection; ventilation

Abstract:

This report investigates the use of the Fire Dynamics Simulator (FDS), for coarse grid modeling of non-fire and fire situations. FDS is a large eddy simulation computational fluid dynamics program that was developed to model fires in enclosures. One goal of this study was to compare its predictions with experimental data and other published CFD studies of test rooms without tires in them. Four such experiments are considered. The first three are idealized test rooms designed to demonstrate forced, natural, and mixed convection. The fourth is a more realistic room setup with furniture, a displacement ventilation system, and a contaminant release. The results of these simulations agree reasonably with the experimental data, provided that care is taken in defining boundary conditions and inputs in a way that is consistent with the intention and capabilities of the model. In particular, some care is needed to define convection coefficients for heated or cooled surfaces. A second goal of this study WAS to determine the effects of using very coarse grids on both the computational results and computing time. The results of this comparison show that non-fire simulations are generally much faster than fires because the simulation times step is limited by the convection motion. In many cases, the coarse grid solutions agreed with the experimental data nearly as well as could be accomplished with a much finer grid and could be modeled in real time or faster. However, accurate contaminant dispersal modeling did require a significantly finer grid.