ffireA ffast solver for buoyant fire dynamics,

tracer sources and dispersion

September 2017

Author: Andras HorvathE-Mail: andras.horvath@rheologic.atAffiliation: Rheologic GmbH, www.rheologic.netTested versions: dev, 5.0Document licence: Creative Commons Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0)

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1 Introduction

ffire is a custom solver for the OpenFOAM® framework developed by Rheologic GmbH in Vienna(Austria, Europe) in cooperation with Tian Building Engineering Singapore.

Solver features and capabilities:

� unsteady, density based solver for

� turbulent buoyant flows including

� radiative heat transfer, multiple species sources, transport of species and

� customisable sources for heat, soot and CO (carbon monoxide)

Contrary to established solvers like fireFoam, open source simulations systems like FDS (Fire DynamicsSimulator) or commercial products like ANSYS-CFX chemical reactions are not modeled in ffire .Realistic, previously measured, unsteady heat release rate curves are zonaly applied to the simulatedgeometry and tracers like soot and CO are produced proportionally in user selactable volume zones.Tracer production is coupled to heat release rate and known, pre-defined conversion factors of differentfuels. ffire therefore is agnostic to the fuel burnt.

Advantages of ffire :

� simplification of models and assumptions

� very good parallel speed up and short solution times

� support for arbitrary (polyhedral) meshes and complex geometries

� support for unsteady heat release rates and multiple fire locations

2 Solver validation

Solver accuracy was tested against validation cases. One classic experiment for buoyancy driven firedynamics is the so called ”Stecker room” experiment1. Experimental set-up see Fig. 1.

A subset of Steckler’s experiments was simulated and results were compared to experimental data.Validation data include measured and simulated temperatures and velocities. Simulations were rununtil a pseudo-steady state was reached for the temperature and flow-field at the measurementpositions. Presented data are evaluated at the vertical center-line of the door.

Please note that ”outside” temperature for all validation simulations was chosen to be constant at293 K. Steckler notes that the temperature outside the room was not constant between differentexperiments and estimates the error due to fluctuating outside temperature to be small/negligible.

Table 1 shows which experiments were simulated for validating ffire .

1K. D. Steckler, J. G. Quintiere, W. J. Rinkinen: Flow Induced by Fire in a Compartment, U.S. Department ofCommerce, National Bureau of Standards, NSBIR 82-2520 (1982)

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Experiment No. door configuration burner power (kW)

14 6/6, fully open 62.919 6/6, fully open 31.620 6/6, fully open 105.321 6/6, fully open 158.0

Table 1: Subset of Steckler’s experiments used for validation

Figure 1: Experimental set-up of the ”Steckler room”.

3 Solution speed

Time to solution (like with every CFD code) depends on many factors including mesh density, totalnumber of finite volume cells, geometry, volumetric heat source power, radiation model, etc.

Validation cases are compared for time to solution in the table below to give a first impression ofsolution speed. The mesh for validation cases consisted of 307000 mostly hex-cells. Simulations wererun 8x parallel on an Intel Xeon E5-2620 v4 with DDR4 RAM clocked at 2133 MHz.

Case Solution time (hh:mm) rad. model

19 6/6 31.6 2:18 fvDOM14 6/6 62.9 5:13 fvDOM20 6/6 105.3 3:47 fvDOM21 6/6 158.0 2:34 P1

Table 2: Wall-clock time to simulate 60 s for different cases and settings

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Figure 2: Validation of temperature (top) and velocity (bottom) for experiment 19 6/6, P=31.6 kW

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Figure 3: Validation of temperature (top) and velocity (bottom) for experiment 14 6/6, P=62.9 kW

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Figure 4: Validation of temperature (top) and velocity (bottom) for experiment 20 6/6,P=105.3 kW

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Figure 5: Validation of temperature (top) and velocity (bottom) for experiment 21 6/6,P=158.0 kW

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4 Application examples

Figure 6: Postprocessing of a Steckler room validation case. Note the tilted fire zone due to themomentum of natural draft of cool air through the door opening.

Figure 7: Simulation of smoke induced visibility impairment in a large scale geometry (busdepot). Fully evolved fire with smoke spreading directly below ceiling. No forced ventillation.

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Figure 8: Simulation of smoke induced visibility impairment in a large scale geometry, 17 minutesand 51 seconds after start of simulation. Visibility is severly reduced due to sooting combustion.

Figure 9: Geometry used for large scale fire and smoke simulation. Fire location is marked inred, view-point of visualisation in green. The mesh consists of 2.73 million finite volume cells.Geometric extents: 64.5 x 116.3 x 7.8 m.

Rheologic GmbHLiniengasse 40/121060 ViennaAustria

andras.horvath@rheologic.netwww.rheologic.net+43 699 819 032 36

Legal disclaimer:

This offering is not approved or endorsed by OpenCFD® Limited, the producer of the OpenFOAM® ,software and owner of the OpenFOAM® and OpenCFD® trade marks. OpenFOAM® is a registeredtrade mark of OpenCFD® Limited, the producer of the OpenFOAM® software.