Numerical Modeling Of Scaled Down Fire Experiments

The Froude-number based reduced-scale modeling is a technique commonly used to calculate the flow of heat and mass in building fires. The ratio of internal forces to the bouncy forces, plays a pivotal role within these equations. Unlike computer simulations, fire physical tests cannot always be performed. The most common limitations are high costs of such tests, long preparation time and lack of repeatability of the tests. Additionally, for really small scales finding appropriately tiny measuring devices can be a problem. Computer models are continually gaining accuracy, as is the scope of the modeled fire phenomena. However, due to limitations in representation of many fire-related phenomena, computational costs, and uncertainties related to numerical investigation, the fire simulations in reduced-scale modeling, still are not popular tool.

In the conducted tests the credibility of Computational Fluid Dynamics (CFD) software code FDS has been tested. To do this two physical tests has been performed. The small heptane fire (approximately 150 kW) was used as a start point in full scale. After that the fire compartment was geometrically reduced four times (to scale 1:4). The fire parameters were calculated accordingly using the mentioned above Froude-number method. In the FDS code, physical tests were reproduced and additional calculations in scales (1:2, 1:10, 1:20, 1:50) were performed. For comparison and determination of the applicability range, temperature was used as the parameter that is not scalable and should be the same.

The results show that the applicability of numerical modeling of scaled down fire experiments has limitations related to the scale. The numerical representation of fire tests up to the scale of 1:10 is at high accuracy level, but for bigger reduction the accuracy is lower. Currently the additional experiments with higher HRR (up to 5.3 MW) are being prepared.