James Allen

Simulating fire / smoke in FloSim

Discussion created by James Allen on Jun 15, 2011
Latest reply on Jun 30, 2011 by James Allen



To support a recent enhancement request Im looking to gauge user interest in simulating fire / smoke in Flosim for development of HVAC system designs. The more people we get onboard the greater likelihood the development team at Dassault Systemes will include this feature in a future release.


We currently use Ansys CFX to model all of our fire simulations in enclosed car parks and tunnels (large well ventilated enclosures). The methodology we use is an inert heat source. Combustion models are also used but that is beyond the scope of this discussion.


I have recently developed a way of simulating an inert fire in Solidworks Flosimulation with very good results. We can produce results in a much shorter timescale than it would take in CFX (within 1 day compared to many days in CFX) so it is of real interest to us to
invesigate this further.


To use Flosimulation for all fire simulation work we would need to be able to simulate smoke. One method of doing this in CFX is to simulate the smoke as an additional variable defined as a scalar quantity (with units kg/kg) i.e. smoke is expressed as a
mass fraction and assumed to have the same properties as the primary fluid.


The scalar quantity which is user defined needs to be linked to the transport equation so
it is carried through the fluid domain with the convective and forced flow terms. The
additional variable is defined from a user expression using a yield factor and the heat of
combustion of a given fuel.


In post processing we create a user defined variable to calculate visibility which can be
done simply by emperical formulae from the mass fraction of the scalar.


So in summary there are three features we would like to see developed:


1. ability to create an additional variable that can be linked to the transport equation.
2. ability to create user expressions to define 'smoke massflow' and 'visibility'
3. ability to create a user variable as a post processing feature which is equal to the
expression 'visibility' (with units in metres).


Cheers taking time to read this . I look forward to reading your comments and ideas on this subject.