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The Official Website of Dr. John H. Klote, PE - Updated November 6, 2015

Smoke is the major killer in building fires, and smoke control

provides significant protection from the threat of smoke.

Computational Fluid Dynamics (CFD)

Atrium smoke control is conventionally analyzed with a group of algebraic equations, but computational fluid dynamics (CFD) has capabilities that far exceed the algebraic equation approach. Before CFD was used for atrium smoke control, it was used for a wide range of applications including aircraft design, automotive design, boiler design and weather forecasting. At one time, CFD was restricted to teams of scientists and engineers using super computers that cost millions of dollars, but advances in computer hardware and software have put CFD within the reach of even the smallest engineering design and consulting firms. Unlike analysis by algebraic equations, a single CFD simulation takes many hours or even days of computer time, and a number of CFD simulations are usually needed to analyze an atrium smoke control system.

In the 1970s, computational fluid dynamics (CFD) was developed at the Imperial College in the United Kingdom, and now there are many CFD models that can be used for smoke control analysis. Fire Dynamics Simulator (FDS) is a CFD model that was developed at the National Institute for Standards and Technology (NIST) specifically for fire applications. Because it is a product of NIST, FDS is available at no cost. For these reasons, FDS have become the de facto standard CFD model for atrium smoke control in the U.S.

The idea of CFD modeling is to divide a space into a large number of smaller spaces called cells, and use a computer to solve the governing equations for the flows, pressures, and temperatures throughout the large space. The governing equations consist of at least the equations for conservation of mass, conservation of momentum, and conservation of energy. These conservation equations are nonlinear partial differential equations, and solution of these equations requires what is called a numerical solver. These solvers are written in high level computer languages such as FORTRAN. Readers should be aware that it is absolutely impossible to do CFD modeling with any spreadsheet program.

CFD has the capability to deal with complex atrium smoke control design challenges in ways that the algebraic equation approach cannot. Major advantages of CFD are (1) it can simulate smoke flow in atria with complex shapes, and (2) it can analyze tenability. The algebraic equation approach can only be used with atria of simple geometry. The algebraic equation approach is based on the idea of keeping the smoke away from the occupants, but the CFD approach can be used to maintain a tenable environment. A tenable environment is one in which the products of combustion including heat are limited to a level that is not life threatening.

CFD software generates such enormous quantities of data that conventional methods of presenting and analyzing data are inadequate. If the output of a medium size CFD atrium simulation were printed on letter size paper and put in cardboard boxes, the boxes could easily fill a conference room from floor to ceiling. So that people can understand CFD output, postprocessing software has been developed. This software produces graphic representations of CFD simulations, and many CFD models have postprocessing software specifically written for them. Smokeview was written for FDS, and can produce a 3-D representation smoke flow in an atrium.

CFD modeling requires a high level of expertise. Properly done CFD analysis is capable of realistically simulating smoke movement as no other kind of computer model can. CFD modeling lends itself to tenability analysis. CFD simulations can include wind effects. For a more detailed overview of CFD modeling, see Chapter 20 of the Handbook of Smoke Control Engineering.

CFD is capable of realistic smoke flow simulations, and it can be used for analysis of complex atrium smoke control systems.

CFD is capable of realistic fire simulations.

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