Practical Application of the LES Method to Mixing in Large Indoor Spaces

Abstract

The scope of protecting public venues in the U.S. is staggering in the areas of money, time and experience at doing this sort of thing. Derivation of protection strategies for the building infrastructure will necessarily involve a combination of experiments and computer simulations to provide confidence in building design or retrofit before the needed dollars and time are committed. Computer simulation can be less costly and be performed in shorter times than experiments even when the building of interest is quite large and thus, will be used extensively now and in the future for building protection design. This paper specifically targets the accuracy and application of computational fluid dynamic (CFD) codes for prediction of mixing behavior. The ability to determine the nature, make correct identification and quantify the amount of a release from a chemical or biological weapon (CBW) relies in part on understanding the underlying physics of air propagation throughout the domain. Specifically, we must understand the rates at which a contaminant may mix throughout the domain. Turbulent mixing is a function of the range of spatial and temporal scales found in the domain, i.e., the large scale eddies (on the size of the domain) advecting the contaminant, the small scale eddies (inertial range) “mixing” the contaminant as it is being advected and the time scales corresponding to these eddy sizes. The widely used Reynolds Averaged Navier-Stokes (RANS) numerical modeling methods cannot capture the time dependent motions which are responsible for a significant amount of mixing. The Large Eddy Simulation (LES) method is based on simulating the turbulent fluctuations that can be resolved by the mesh while the smaller eddies are modeled. The LES method can produce more information about the nature of the flow field than RANS. This paper discusses the application of the LES method, specifically an LES/DES (Detached Eddy Simulation) coupled method, to simulate mixing in a realistically scaled fictitious airport. Application of the LES method such as determination of what eddy size to resolve, transient startup effects, determination of eddy turnover time and others are discussed. This research is sponsored by Department of Homeland Security under Air Force Contract F19628-00-C-0002. The views expressed are those of the author and do not reflect the official policy or procedure of the United States Government.