FLAIR Tutorial 10: Fire and Smoke Modeling

This example provides step-by-step instructions on how to activate a FIRE object for a typical t-squared fire and set the relevant smoke production and visibility parameters. In the second part of the tutorial, a pair of jetfans is introduced to try to blow the smoke away from one side of the domain. In the third stage, In-Form is used to modify the jetfans so that they activate when the temperature at a monitor point rises above a trigger value. The geometry of the case is shown in the figure below.

The size of the domain is 10m long x 10 m wide x 3 m high. A fire is located on the floor in the middle of the domain. All four vertical faces of the domain are open to atmosphere.

The fire obeys a t2 law, Q=a.t2, where the a constant is set for a 'fast' fire as per Table10.1 of the CIBSE Guide E, Fire Engineering. The heat of combustion, smoke particulate yield and CO yield are set for 'Timber', from Table 10.7 of CIBSE Guide E.

The entire simulation lasts for 300 seconds.

Setting up the model for stage 1

Start FLAIR with the default mode of operation

To activate the physical models

a. The Main Menu panel

b. add the FIRE object

c. add the floor

d. create the first opening

The four vertical faces of the domain are open to atmosphere.

e. create the remaining openings by copying the first

X: untick 'to end' and set 0.0

Y: tick 'to end'

Z: leave 'to end'

X: tick 'at end'

Y: 0.0 m

Z: 0.0 m

f. To set the grid numbers and set solver parameters

g. place the probe

X: 5.0

Y: 5.0

Z: 2.0

Running the solver

To run the PHOENICS solver, Earth, click on 'Run', then 'Solver', then click on 'OK' to confirm running Earth. These actions should result in the PHOENICS Earth monitoring screen.

NOTE: This will run faster using the 'Run', 'Parallel Solver' option if you have the cores available for this and your licence allows it.

As the Earth solver starts and the flow calculations commence, two graphs should appear on the screen. The left-hand graph shows the variation of solved variables at the monitoring point that was set during the model definition. The right-hand graph shows the variation of errors as the solution progresses.

Viewing the results

Once the solver has completed step 1 and has started on step2, we can start to plot the results of step 1.

Saving the case

Once a case has been completed, it can be saved to disk permanently by clicking 'File - Save as a case'. Enter 'No fans' as the name of the case, then click Save. Click OK to save the intermediate step files also. These will be saved to a folder called 'No fans' created in the current working directory, or wherever the case files were saved.

Setting up the model for stage 2

Adding the jetfans

Jetfans are commonly used in car parks and tunnels to control smoke and air movement. We will now introduce two jetfans, one on either side of the fire.

h. Create the first Jetfan

i. Create the second Jetfan by copying the first

Run the solver, then view the results as before. The solution on step 1 should look like this:

Save the results as a case.

Setting up the model for stage 3

We now want the jetfans to be controlled by a temperature sensor. We want them to activate when the temperature at (5,5,2.9) reaches 60° C. This can be done by adding an InForm command to the jetfans.

j. Add the InForm statements

The solver can now be run as before. The solution at step 3 should be:

and on step 4 the jetfans should have activated:

Once again, save the case.