Encyclopaedia Index

FLAIR Tutorial 9: Fire-spray in a compartment

This example provides step-by-step instructions on how to activate GENTRA module, which solves the dispersed phase equations using Lagrangian methods and how to load and define the spray-head object for the simulation of fire extinction. In-Form is used to define the transient fire source which is the function of time and the concentration of the water vapour. The geometry of the case is shown in the figure below.

The size of the compartment is 2.8m long x 2.8 m wide x 2.2 m high. A sprinkler is mounted at the ceiling of the middle of the compartment. A fire source is located on the floor facing the sprinkler. There is a wall on the right with a door to the open space.

The simulation starts with a growing fire source before the water spray starts when the spray link temperature exceeds 50C. The entire simulation lasts for 120 seconds.

Setting up the model

Start FLAIR with the default mode of operation

• Click FLAIR icon (a desktop shortcut created by the FLAIR installation program); or
• Start the VR-Editor by clicking on 'Start', 'Programs', 'FLAIR', then 'FLAIR-VR'. The VR screen shown in Fig. 2 should appear.
• Click on the 'File' button and then select 'Start new case', followed by 'FLAIR' and 'OK'.

  The FLAIR VR-Environment screen should appear, which shows the default domain with the dimensions 10mx10mx3m.

Resizing the domain

• Change the size to 5m in x-direction, 2.8m in y-direction and 2.2m in z-direction on the control panel.
• Click on "Reset" button, on the movement panel and then click "Fit to window".

To activate the physical models

a. The Main Menu panel

• Click on the 'Main Menu' button. The top page of the main menu will appear on the screen.
• Click on the 'Title' dialogue box. Then type in 'Fire-spray in a compartment'.
• Click on 'Geometry' to obtain the Grid Mesh Settings dialog.
• Change 'Time dependence' from Steady to Transient.
• Click on 'Time step settings' and set the input as shown below

  

• Click on 'OK' twice to close the 'Geometry' panel.
• Click on 'Models' to obtain the Model menu page.
• Switch 'Solve smoke mass fraction' to 'ON' and then 'click on its 'settings'
• This panel is where the heat of combustion and particulate smoke yield are set. See TR/313 Section 4.6 or the on-line help for descriptions of the settings on this panel.

  

  The CIBSE Guide E (2003) provides the following data:

  Material	Hfu (MJ/kg)	Yco (kg/kg)	Ys (kg/kg)
  Timber	13.0	0.020	<0.01 - 0.025
  PVC- Polyvinyl chloride	5.7	0.063	0.12 - 0.17
  PU- Polyurethane (flexible)	19.0	0.042	<0.01 - 0.23
  PU- Polyurethane (rigid)	17.9	0.18	0.09 - 0.11
  PS- Polystyrene	27.0	0.060	0.15 - 0.17
  PP- Polypropylene	38.6	0.050	0.016 - 0.1

  If the fire is to represent burning timber, set the 'Heat of Combustion' to 1.3E7 and the 'particulate smoke yield' to 0.02. Click 'Update Rox' to bring the stoichometric ratio in line with the new heat of combustion.

• Switch 'Sight length for light-reflecting objects (SLEN)' to 'ON'.
• Click on 'Previous panel'.
• Click on 'Top menu' and 'OK' to close the main menu.
• Adding the object to the calculation domain

b. add the spray-head

• Click on the 'Object' pull-down menu and select the 'New' (New Object) option on the 'Object management' dialog box to bring up the 'Object specification' dialog box.
• Change 'Name' to 'Spray'
• Select 'Spray-head from the object 'Type' list and then click on 'OK' to activate GENTRA.
• Click on 'General' and then click on 'attributes'.
• Set the 'Spray position' to 1.49 in X, 1.4 in Y and 2.1 in Z. This sets the position of the centre of the spray head.
• Set the 'Spray radius' to 0.05. The size and position of the object will be updated when the Object Specification dialog is closed.
• Change 'Activate all the time' from 'Yes' to 'Auto-on'. New buttons relating to the link temperature calculation will appear. Set 'Activation temperature' to 50 C. Leave the spray duration as 120 s, as this will ensure the spray does not stop.
• Set the rest of input as shown below. Please refer to TR/313 Section 3.1.4 for the definition of each entry.



• Click on 'OK' to return to the 'Object management' dialog box. The GENTRA particle Tracker will be turned on automatically, with all the correct settings for the spray model. Only the spray start and end-times need to be set.

c. add the fire source

• Click on the 'Object' pull-down menu and select the 'New' (New Object) option on the 'Object management' dialog box to bring up the 'Object specification' dialog box.
• Change 'Name' to 'Fire'
• Click on the 'Size' button and set 'Size' of the object as:

  X: 0.5 m

  Y: 0.5 m

  Z: 0.3 m

• Click on the 'Place' button and set 'Position' of the object as:

  X: 1.25 m

  Y: 1.125 m

  Z: 0.0 m

• Click on 'General' and then 'attributes'.
• Set the material to 'Domain material'.
• Click on 'In-Form Commands'. The Inform Sources dialog will appear.
  • Click 'Add Inform'.
  • Click the empty button under 'Keyword' and select SOURCE.
  • Click the empty button under 'Var' and select TEM1.
  • Click the empty button under 'Formula'. An editing window will appear. In the input window, type

  (exp(-500.*MH2O)*46.9*tim)*tim

  then click 'File', 'Save & Exit'. An explanation of the settings made is given shortly!

  • Click the empty button under 'Condition'.  An editing window will appear. In the input window, type

  whol

  then click 'File', 'Save & Exit'.

  • Click 'Add Inform' again.
  • Click the empty button on the second row under 'Keyword' and select SOURCE.
  • Click the empty button under 'Var' and select P1.
  • Click the empty button under 'Formula'. An editing window will appear. In the input window, type

  (exp(-500.*MH2O)*46.9*tim)*tim*(1+rox)/hcomb

  then click 'File', 'Save & Exit'.

  • Click the empty button under 'Condition'.  An editing window will appear. In the input window, type

  whol

  then click 'File', 'Save & Exit'.

  • Click 'Add Inform' again.
  • Click the empty button on the second row under 'Keyword' and select SOURCE.
  • Click the empty button under 'Var' and select SMOK.
  • Click the empty button under 'Formula'. An editing window will appear. In the input window, type

  1

  • Click the empty button under 'Condition'.  An editing window will appear. In the input window, type

  onlyms

  then click 'File', 'Save & Exit'.

  • The In-Form Sources dialog should now look like this:

    

  Please note that the above function is only for the purpose of demonstration. InForm is used to show how the local vapour concentration (MH2O) can be used to reduce the heat source from the fire.

  The heat source Q is a function of time (tim) and the local water vapour mass fraction (MH2O). As long as the MH2O values are near zero, the expression gives a t² fire growth. The constant 46.9 is appropriate for a 'fast' fire. Once MH2O increases, the strength of the fire is reduced. The -500 multiplier determines how much the source is reduced.

  The first line sets the mass source as Q*(1+stoichometric ratio)/(heat of combustion), where rox and hcomb are the internal menu names. The second line sets the heat source, and the last line sets the mass fraction of combustion product in the incoming stream to 1. The 'whol' qualifier means that the source is a total source for the object. The 'onlyms' qualifier means that the quantity set by the source is convected in by the associated mass source.  For more information on InForm, click here.

• Click on 'OK' and 'OK'.

d. create the wall with a door

The wall is made of three blockages.

• Click on the 'Object' pull-down menu and select the 'New' (New Object) option on the 'Object management' dialog box to bring up the 'Object specification' dialog box.
• Change 'Name' to 'BLK1'
• Click on the 'Size' button and set 'Size' of the object as:

  X: 0.1 m

  Y: 1.03 m

  Z: tick 'to end'

• Click on the 'Place' button and set 'Position' of the object as:

  X: 2.8 m

  Y: 0.0 m

  Z: 0.0 m

• Click on 'OK' to exit from the object specification dialog.
• Click on the 'Object' pull-down menu and select the 'New' (New Object) option on the 'Object management' dialog box to bring up the 'Object specification' dialog box.
• Change 'Name' to 'BLK2'
• Click on the 'Size' button and set 'Size' of the object as:

X: 0.1 m

Y: 1.05 m

Z: tick 'to end'

• Click on the 'Place' button and set 'Position' of the object as:

X: 2.8 m

Y: tick 'at end'

Z: 0.0 m

• Click on 'OK' to exit from the object specification dialog.
• Click on the 'Object' pull-down menu and select the 'New' (New Object) option on the 'Object management' dialog box to bring up the 'Object specification' dialog box.
• Change 'Name' to 'BLK3'
• Click on the 'Size' button and set 'Size' of the object as:

X: 0.1 m

Y: 0.72 m

Z: 0.37 m

• Click on the 'Place' button and set 'Position' of the object as:

X: 2.8 m

Y: 1.03 m

Z: tick 'at end'

• Click on 'OK' to exit from the object specification dialog.

e. add the wall on the high-Y side

• Click on the 'Object' pull-down menu and select the 'New' (New Object) option on the 'Object management' dialog box to bring up the 'Object specification' dialog box.
• Change 'Name' to 'WALL1'
• Click on the 'Size' button and set 'Size' of the object as:

  X: 2.8 m

  Y: 0.0 m

  Z: tick 'to end'

• Click on the 'Place' button and set 'Position' of the object as:

  X: 0.0 m

  Y: tick 'at end'

  Z: 0.0 m

• Click on 'General' and select 'PLATE' from the object 'Type' list.
• Click on 'Attributes'.
• Change 'Energy source' from 'Adiabatic' to 'Surface temperature' and enter the value to 20°C
• Click on 'OK' twice to close the object specification dialog box.

f. add the wall on the low-Y side

This wall is made by the duplicating method.

• Click on the wall object, WALL1
• Click on the ' Duplicate object' button on the control panel and 'OK' to confirm the action.
• Move the position of the duplicated object to:

  X: 0.0 m

  Y: 0.0 m

  Z: 0.0 m

• Double click on the duplicated object to bring up the object specification dialog box.
• Change the 'Name' to WALL2 and click on 'OK'.

g. add the wall on the low-X side

• Click on the 'Object' pull-down menu and select the 'New' (New Object) option on the 'Object management' dialog box to bring up the 'Object specification' dialog box.
• Change 'Name' to 'WALL3'
• Click on the 'Size' button and set 'Size' of the object as:

  X: 0.0 m

  Y: tick 'to end'

  Z: tick 'to end'

• The 'Position' of the object will be left to its default :

  X: 0.0 m

  Y: 0.0 m

  Z: 0.0 m

• Click on 'General' and select 'PLATE' from the object 'Type' list.
• Click on 'Attributes'.
• Change 'Energy source' from 'Adiabatic' to 'Surface temperature' and enter the value to 20° C
• Click on 'OK' twice to close the object specification dialog box.

h. add the floor

• Click on the 'Object' pull-down menu and select the 'New' (New Object) option on the 'Object management' dialog box to bring up the 'Object specification' dialog box.
• Change 'Name' to 'FLOOR'
• Click on the 'Size' button and set 'Size' of the object as:

  X: tick 'to end'

  Y: tick 'to end'

  Z: 0.0 m

• The 'Position' of the object will be left to its default :

  X: 0.0 m

  Y: 0.0 m

  Z: 0.0 m

• Click on 'General' and select 'PLATE' from the object 'Type' list.
• Click on 'Attributes'.
• Change 'Energy source' from 'Adiabatic' to 'Surface temperature' and enter the value to 20°C
• Click on 'OK' to close the object specification dialog box.

i. add the ceiling

This is made by the duplicating method.

• Click on the plate object, FLOOR
• Click on the ' Duplicate object' button on the control panel and 'OK' to confirm the action.
• Move the position of the duplicated object to:

  X: 0.0 m

  Y: 0.0 m

  Z: tick 'at end'

• Change the X size of the duplicated object to 2.8m.
• Double click on the duplicated object to bring up the object specification dialog box.
• Change the 'Name' to CEILING and click on 'OK'.

j. add the openings

These objects will provide the boundary conditions to the open space.

• Click on the 'Object' pull-down menu and select the 'New' (New Object) option on the 'Object management' dialog box to bring up the 'Object specification' dialog box.
• Change 'Name' to 'OPN1'
• Click on the 'Size' button and set 'Size' of the object as:

  X: 2.1 m

  Y: 0.0 m

  Z: tick 'to end'

• The 'Position' of the object will be left to its default :

  X: 2.9 m

  Y: tick 'at end'

  Z: 0.0 m

• Click on 'General' and select 'OPENING' from the object 'Type' list.
• Click on 'Attributes'.
• Change 'External turbulence' from 'In-Cell' to 'User-set'.
• Click on 'OK' twice to close the object specification dialog box.

Now we create other openings by the duplicating method.

• Make sure that the above created opening is highlighted.
• Click on the 'Duplicate object' button and 'OK' to confirm duplicating.
• Move the duplicated object to:

X: 2.9 m

Y: 0.0 m

Z: 0.0 m

• Double click on the duplicated object to bring up the object specification dialog box.
• Change the 'Name' to 'OPN2'
• Click on 'Duplicate object' and 'OK'
• Double click on the duplicated object to bring up the object specification dialog box.
• Change the 'Name' to 'OPN3'.
• Click on the 'Size' button and set the size of OPN3 to:

X: 0.0 m

Y: tick 'to end'

Z: tick 'to end'

• Click on the 'Place' button and set the position of OPN3 to:

X: tick 'at end'

Y: 0.0 m

Z: 0.0 m

• Click on 'OK' to close the object specification dialog box.
• Click on the 'Duplicate object' button and 'OK'
• Double click on the duplicated object to bring up the object specification dialog box.
• Change the 'Name' to 'OPN4'.
• Click on the 'Size' button and set the size of OPN4 to:

X: tick 'to end'

Y: tick 'to end'

Z: 0.0 m

• Click on the 'Place' button and set the position of OPN4 to:

X: 2.9 m

Y: 0.0 m

Z: tick 'at end'

• Click on 'OK' to close the object specification dialog box.
• Exit from the Object management dialog box as all the objects for this simulation were created.

k. To set the grid numbers and to solver parameters

• Click on the main 'Menu' button and then click on 'Geometry'
• Switch the grid in X, Y and Z from 'Auto' to 'Manual', then set the number of cells as follows:

  	X	Y	Z
  Total number of cells	31	21	17
  Region 1	10 (Power -1.2)	7	3
  Region 2	2	1	11
  Region 3	1	2	2
  Region 4	2	1	1
  Region 5	10 (Power 1.2)	2	(n/a)
  Region 6	1	1	(n/a)
  Region 7	5 (Power 1.5)	7	(n/a)

  Note that the number of regions were generated automatically based on how the objects divide the domain in each direction. To set the grid in the regions, click 'Edit all regions in' for each direction in turn.

• Click on 'Apply' to apply the changes and then 'OK' to close the Grid mesh Settings.
• Click on 'properties'. The ambient pressure is set to 0Pa relative to 101325 Pa (1 atm), and the ambient temperature to 20°C.  These values are correct for this example. The ambient values ae used as the default external temperature and pressure at all inlet and opening objects.
• Click on 'Sources' . The 'Reference density' has been deduced from the ambient conditions set on 'Properties'. If this is incorrect, the buoyancy forces may set up unrealistic flows at the openings where the pressure is fixed. The reference density is updated whenever the ambient conditions are changed.
• Click on 'Initialisation'. The initial value (FIINIT) for TEM1 and p1 are set to 'ambient' to show that they will take the current ambient values.
• Click on 'Numerics', then 'Relaxation settings' and set

Variable	MH2O	TEM1
LINEAR	0.3	0.25
MAXINC	0.5	10

• Click on 'Output' and set the Monitor-cell location:

IXMON = 14, IYMON = 11, IZMON = 8

• Click on 'settings of the 'Field dumping' and set 'Intermediate field dumps':

Set 'Step frequency' to 1.( Zero for first and last step means always start at step 1 and end at the last step).

• Set the 'Start letter for PHI'  to m.
• Click on 'Previous panel' , 'Top menu' and then 'OK'.

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.

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

• Click on the 'Run' button, then on 'Post processor', then 'GUI Post processor (VR Viewer)' in the FLAIR-VR environment.
• When the 'File names' dialog appears, change 'Use intermediate step files' to 'Yes' and click 'OK' to accept the current result files.
• Click on the 'Macro' button on the control panel.
• Change 'MACRO file' to GHIS and then click on 'OK'. Note that tracks are only drawn on the time step to which they relate. There will be no tracks for the first 5 steps.
• Click on the 'Y' (Slice direction Y) button and move the probe position Y to 1.45m
• Click on 'T' (Select temperature) button, followed by the 'Contour toggle' button, .
• Click on the 'Run animation' button, . The animation will start which shows that the temperature increases with time first and then decreases as soon as the spray has started.
• A typical picture is shown below.

  

• Iso-surfaces of temperature at, say, 60 C can also provide an insight into how the spray cools the air in the compartment.

Saving the case

Once a case has been completed, it can be saved to disk as a new Q1 file by 'File - Save working files'. The Q1 and associated output files can be saved more permanently by 'File - Save as a case'.