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Verification of CFD modeling for smoke control using two compartment fire experiments.

Article Excerpt
INTRODUCTION

In parallel with the development of numerical models and the increasingly broader range of applications of computational fluid dynamics (CFD), the need for verification and validation (V&V) in CFD has been recognized by both academic researchers and industry practitioners. For example, the American Society of Mechanical Engineers (ASME) Fluid Engineering Division (FED) long ago enforced a policy on controlling numerical accuracy (Roache et al. 1986); the American Institute of Aeronautics and Astronautics (AIAA) has developed a guide on CFD V&V (AIAA 1998), which provides generic definitions and procedures for model verification and validation; and ASHRAE has addressed CFD through its technical committee publication on Indoor Environment Modeling (ASHRAE 2005). The AIAA (1998) defines V&V as follows:

* Verification: The process of determining that a model implementation accurately represents the developer's conceptual description of the model and the solution to the model.

* Validation: The process of determining the degree to which a model is an accurate representation of the real world from the perspective of the intended uses of the model.

For numerical models for fire safety research and applications, a position statement on V&V from the International FORUM of Fire Research Directors was published recently (Gritzo et al. 2005), which is essentially derived from AIAA (1998). Similarly, a number of standard guides are being maintained by the American Society for Testing and Materials (ASTM) on deterministic fire models, including algebraic, zone, and CFD models (ASTM 2004). Industry-specific fire model applications, such as for nuclear power plant applications (NRC 2007), have also been developed from the users' perspective. The position statement by the International FORUM of Fire Research Directors recommends the following V&V activities for fire model application (Gritzo et al. 2005):

* Code verification by the developer to identify and reduce coding errors

* Calculation verification, including characterization of discretization (normally grid) and input parameter dependence to establish appropriate model usage

* Model validation in the parameter space of interest, based on an established metric and employing high-quality experimental data, to provide a quantitative assessment of the predictive capabilities of a model

* Documentation of validation studies, following established guidelines, in the open literature with sufficient rigor and detail to be used as a basis for increased confidence in future analyses

It should be noted that, among all types of CFD applications in fire engineering, a significant percentage is in the area of smoke control (McGrattan 2005). For smoke control design and analysis, CFD is advantageous, as it allows for detailed examination of the spatial distribution of smoke by taking into account the buoyancy from the fire heat, the forced convection from wind or mechanical ventilation, and the interaction with building obstructions and walls. For complex building environments and unconventional types of structures, CFD has been shown to be especially valuable in the design of smoke management systems (Klote and Milke 2002). Applications of CFD to smoke control include, for example, atria (Hadjiso-phocleous et al. 1999), shopping centers, airport terminals, tunnels (Kang 2006a), mass transit stations (Kang 2006b), car parks, residential apartments (McGrattan and Forney 2006). V&V of CFD in smoke control applications has also been examined in a number of studies (e.g., McGrattan et al. [1998], Jill et al. [2003], and Kang 2006a).

A compartment fire is one of the fundamental elements in building fire safety, and is probably the most widely studied. For example, a compartment fire could represent a retail store fire in a shopping center or a hotel room fire. In addition, a compartment fire such as the ISO-9705 full-scale room fire test represents the simplest form of enclosure fire dynamics. Experiments of compartment fires have been used to investigate various types of fire-related issues, such as the material burning behavior and the effect of ventilation (Karlsson and Quintiere 2000). A compartment fire offers well-defined and controllable conditions such that detailed, accurate, and reproducible measurements are possible for the parameters of interest for fire behavior in a confined environment. This approach is valuable for verification and validation of numerical fire models. V&V for CFD modeling in compartment fires has thus been studied extensively (e.g., Zou and Chow [2005], Rein et al. [2006]) and still remains critical to fire safety engineering (Cox and Kumar 2002).

In this paper, two sets of compartment fire experiments are examined. They are the fire tests conducted by Steckler et al. (1982) and the tests by Shields et al. (2002). From the published experimental data, both quantitative and qualitative comparisons are made with the numerical predictions. These two case studies provide a means for verifying CFD modeling in smoke control applications, as well...

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