Journal Article Reports on Approaches to Improve Convection Models in the Fire Dynamics Simulator
The peer-reviewed journal article “Toward Grid-Independent Modeling of Natural Convection with Fire Dynamics Simulator” has been published in the International Journal of Heat and Mass Transfer journal. The paper was authored by Parham Dehghani, Dushyant Chaudhari, Matthew DiDomizio, and Jason Floyd from the Fire Safety Research Institute (FSRI), part of UL Research Institutes, as part of the Fire Modeling Development and Validation research project.
Although not limited to just the Fire Dynamics Simulator (FDS), this study aimed to improve the accuracy of convection heat transfer predictions in the FDS, even when using large grids. Accurate predictions of convection heat transfer are crucial for understanding how fire spreads and impacts buildings.
Researchers examined three different approaches to improve FDS accuracy
Grid size refers to the size of the small blocks or cells used to divide up the room or building being simulated in the FDS, similar to how Lego blocks divide up a house. Larger grid sizes are common in fire safety engineering because they simulate complex fires in extensive spaces, such as large buildings or industrial facilities. However, larger grid sizes may not capture the detailed physics of convection heat transfer as accurately as smaller grids, so it can be challenging when using the FDS to predict convection heat transfer accurately.
The researchers explored three methods to reduce grid dependency and improve the accuracy of predicting convection heat transfer with FDS:
- The use of a more precise temperature measurement from cells further from the wall, rather than the cells right next to the wall, to improve accuracy;
- The development of a new correlation that related various factors, such as temperature difference and flow properties to provide consistent and reliable predictions, no matter the grid size; and
- The use of wall functions (e.g., curve fitting over dimensionless velocity and temperature profiles)approach to predict temperatures at different heights above the ground for a vertically aligned surface.
Two approaches led to a marked improvement in the accuracy of the current FDS
The first two methods significantly improved the accuracy of convection heat transfer predictions in fire simulations, representing a marked improvement of the existing FDS model. The third method needs further refinement and analysis to obtain grid-independent predictions for convection.
“Convective heat transfer plays a critical role in fire dynamics, and accurate prediction of it is essential for fire safety analyses and engineering design. This study directly addresses the issue of grid dependency in FDS through a systematic grid sensitivity analysis on a simplified yet fundamental geometry, e.g., a vertical wall subject to convective heating. Such a configuration is commonly present in many fire safety scenarios. The case is intentionally simplified by assuming a constant wall temperature and excluding direct flame contact, allowing for focused evaluation of natural convection modeling. Given the complexity of convection, which often involves numerous interacting parameters, this work adopts a structured approach by beginning with a fundamental case. The insights gained from this study serve as a foundation for extending the analysis to more complex fire scenarios in future works.”
—Parham Dehghani, research engineer, FSRI
This research sought ways to make accurate predictions of convection heat transfer even when using larger grid sizes, which are more practical for large-scale simulations like those needed in fire safety engineering. By evaluating and refining methods to reduce grid dependence, the study aims to make fire growth simulations more reliable while maintaining computational efficiency. This research paves the way for more accurate risk assessment and better-informed decision-making in fire safety engineering, representing a critical step forward in using the FDS to protect lives and property from the effects of fire.
About International Journal of Heat and Mass Transfer:
The International Journal of Heat and Mass Transfer publishes high-impact research exploring the underlying physics or fundamental mechanisms governing fluid dynamic processes or/and heat transfer processes. The Journal seeks to publish novel contributions presenting original experimental or simulation results, developments in modeling or data-driven methods with an emphasis on describing novel insights into phenomena or unique features in fluid flow or/and heat transfer. Thematically related papers contributing to advances in engineering design and applications are welcome. The Journal encourages high-quality original contributions to transdisciplinary applications, including low-carbon/green power conversion system; thermo-acoustic interactions; micro/nano-scale thermos-fluidics; biological and environmental flows; flow-induced vibrations; and thermal and/or flow control.
