fire computer modelling at sp fire researchhani/ofgbg15/ofworkshop2015chen151105… · fire...
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Fire Computer Modelling at SP Fire Research
Johan Anderson and Chen Huang [email protected]
[email protected] Acknowledgement: Haukur Ingasson, Mia Kumm, Ying Zhen Li, Robert Svensson,
Marcus Runefors, Bjarne Husted
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Computational work/codes
Heat transfer
Structural mechanics – Abaqus, Safir
CFD – FDS, OpenFoam/FireFoam
Multiphysics – Comsol
Risk and evacuation simulations – Simulex, FDS-EVAC
Around 10 researchers working full time on
simulations.
Fire test of a battery module
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CFD
Aim: Compute smoke spread and temperatures in large compartments.
Evaluate boundary conditions on objects imposed by a fire and tests performed.
Compute flows in complex geometries.
Tools: FDS and OpenFoam/FireFoam solves NS using the LES approximation for low Mach numbers in combination with heat transfer, combustion physics etc.
Hardware: SP cluster + workstations at SP FR.
Investigation of the Rinkeby fire (left) and simulation of flows in the large fire test hall at SP
A facade test simulation.
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Fire CFD Modelling
Low Mach, large-eddy simulation (LES)
Explicit, second-order, kinetic-energy-conserving numerics
Structured, uniform, staggered grid (FDS)
Simple immersed boundary method for treatment of flow obstructions
Generalized “lumped species” method (simplified chemistry using a reaction progress variable)
Deardorff (or Smagorinsky) eddy viscosity subgrid closure
Constant turbulent Schmidt and Prandtl numbers
Eddy dissipation concept (fast chemistry) for single-step reaction between fuel and oxidizer
Gray gas radiation with finite volume solution to the radiation transport equation
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FireFOAM Activities 1
Comparisons between fire tests and
simulations in FireFOAM.
Objective of the tests where to
investigate the scaling of an enclosure
fire.
The room was instrumented with
thermocouples and PTs, BD probes
and CO2, CO and O2 meters in the
door way.
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FireFOAM Activities 2
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
0 10 20 30 40 50
Mas
s fl
ow
[kg
/s]
Time [s]
Mass flow 20cm FireFOAM
Mass flow 20cm FDS
Comparisons between FDS and
simulations in FireFOAM.
Objective evaluate smoke ventilation
and its dependence on grid sensitivity.
Computing the mass flow out of a
vent in the ceiling. The fire source is a
propane burner placed in a hall that is
18m x 18m x 18m.
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FireFOAM Activities 3
Verification of the radiation model.
Comparisons between FDS and
simulations in FireFOAM.
Finite volume discrete ordinance
method (fvDOM) for radiative heat
transfer.
The radiation-in-a-box example is
available in the verification guide for
FDS.
Comparison between fireFoam, FDS and the analytical solution for three cases 300, 1000 and 3000 solid angles.
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FireFOAM
Turbulent diffusion
flame
pyrolysis
radiation Lagrangian
parcels
Surface film
Code: OpenFOAM-2.2.x, FireFOAM (commit code 5f28904ffd)
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Turbulent Diffusion – Eddy Dissipation Model (EDM)*
𝜔𝑓 = 𝜌
min 𝑌𝑓 ,𝑌𝑜
𝑠
∆𝑡𝐶𝑠𝑡𝑖𝑓𝑓1 − exp −𝐶𝑠𝑡𝑖𝑓𝑓∆𝑡𝑟𝑡
Ethanol pool fire (SP Report 2013:02) *Magnussen, B.F. and B.H. Hjertager, On mathematical modeling of turbulent combustion with special emphasis on soot formation and combustion. Symposium (International) on Combustion, 1977. 16(1): p. 719-729.
Mean reaction rate
𝑟𝑡 = max 𝑟𝑡𝑇𝑢𝑟𝑏, 𝑟𝑡𝐷𝑖𝑓𝑓
𝑟𝑡𝑇𝑢𝑟𝑏 = 𝐶𝐸𝐷𝐶휀
max 𝑘 , 𝑆𝑀𝐴𝐿𝐿
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Fire FOAM Activity 4 – Heat Spread in an Inclined Tunnel
Experimental setup Long tunnel distribution energy or
communication Height difference overturns air
movement Risk for fire rescue Model scale tests at SP, 1:20 Propane burner in middle 17 kW
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Numerical Setup
Sub-models Name Constants
Turbulence compressible LES Smagorinsky 𝐶𝑒 = 1.048, 𝐶𝑘 = 0.02, 𝑃𝑟𝑡 = 1.0
combustion Eddy Dissipation Model 𝐶𝐸𝐷𝑀 = 4.0, 𝐶𝑑𝑖𝑓𝑓 = 0, 𝐶𝑠𝑡𝑖𝑓𝑓 = 1.0
radiation fvDOM, grey mean absorption emission
thermo-physical Idea gas, JANAF coefficients
Soot Off
Parameter Initial value Boundary type
𝑘 [m2/s2] 1.0e-4 inlet/outlet: inletOutlet
promatect/glass: zeroGradient
burner: fixedValue
𝑝 [Pa] 101325 calculated
𝑇 [K] 293.15 inlet/outlet: inletOutlet
promatect/glass/burner: fixedValue
𝐮 [m/s] 0 inlet: fixedValue 1.0
outlet: pressureInletOutletVelocity
promatect/glass: fixedValue 0
burner: flowRateInletVelocity massFlowRate 3.7e-4 [kg/s]
(propane)
Initial and boundary conditions
Summary of sub-models
84 375 cells with a cell size of 2 cm
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Results - Speed in parallelization
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Grid size
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Combustion model constant 𝐶𝐸𝐷𝐶
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Turbulent Prandtl number
𝑃𝑟𝑡 =𝜇𝑡𝛼𝑡
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Validation - Velocity
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Validation - Temperature
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Conclusion
SP FR has long experience in fire simulations using CFD.
The heat spread in an inclined tunnel was simulated using FireFOAM solver in OpenFOAM software package.
Sensitivity study was performed for FireFOAM code in terms of important modelling parameters (grid size, combustion model constant and turbulent Prandtl number). Noticeable effect on the calculated temperature, whereas minor effect on the calculated velocities.
Comparison of calculated velocities and temperatures using FireFOAM and measured ones were performed. It showed that FireFOAM yielded reasonable results.
The project was sponsored by Brandforsk in collaboration with LTH.
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Extra
𝐷∗ =𝑄
𝜌∞𝑐𝑝𝑇∞ 𝑔
25
it is recommended to have 𝐷∗ 𝛿𝑥 value in the range of 4 and 16.
𝐷∗ 𝛿𝑥 value of the three mesh (from fine to coarse) are 3.8, 6.3 and 9.4