init region

[ShehabGamrah]

Can I start an init region at a specific time within simulation, as I want it activated when system reaches steady state. Also, what is the best approach for circular areas to be filled with init region?

[mcgratta]

Only if the INIT line is used to insert particles. You cannot instantaneously change the temperature or species concentration of a region within the domain, as that would wreak havoc with the basic conservation equations. Only particles can magically appear and disappear. One exception to what I just said is that you can remove an OBST which then exposes a region that is filled with the background species at ambient temperature. And even that can sometimes cause problems because it is not something that would happen in reality.

[mcgratta]

I would use the INIT line to create an array of solid particles that would appear and disappear at the designated points in time. Each would inject however much soot to achieve your objective. There's a bit of work on your part to figure out the various inputs. I would start with a silly test case involving 1 particle in a sealed box. If you run into trouble, we can help you with that test case rather than try to debug a massive input file.

[ShehabGamrah]

Thanks, and I had another idea regarding this topic: inserting a massless tracer at my inlet, which is a natural opening (with an extended domain beyond it), and then tracking the time taken for the particles to be removed.

However, I am facing two issues:

How can I insert a massless tracer from a natural opening rather than a supply, and allow it to move based on the airflow pattern rather than with an enforced velocity?

How is the particle age parameter applied? Is it assigned to a 3D slice or to a specific device? I am currently encountering errors when trying to use it.

Any guidance would be appreciated.

[mcgratta]

The best way for anyone to help you is to create a very very simple input file that does what you want (or does not do it because of an error). Then we can run the file and make suggestions.

[ShehabGamrah]

Please find the file attached below.

I would like to introduce tracers after a certain time, once the simulation reaches steady state, from the natural opening (hole) so that they fill the domain ( I have tested this initially with vent supply). I would then like to track the time taken for them to be removed through extraction based on vent extraction velocity which I can't correctly activate or would they automatically be removed at exhaust or based on their age setting.

I am also unsure how to introduce tracers from a natural opening rather than a supply.

My interest is not in the tracer properties themselves, so they can be treated as massless.

&MESH ID='MESH', IJK=32,20,15, XB=0.0,6.4,0.0,4.0,0.0,3.0/

&SPEC ID='WATER VAPOR'/

&PART ID='Tracer',
MASSLESS=.TRUE.,
MONODISPERSE=.TRUE.,
COLOR='GRAY 95',
AGE=60.0,
QUANTITIES(1)='PARTICLE AGE',
PARTICLE_EXTRACTION_VELOCITY=1/
&PART ID='Water',
SPEC_ID='WATER VAPOR',
DIAMETER=500.0,
MONODISPERSE=.TRUE.,
AGE=60.0,
SAMPLING_FACTOR=1/

&SURF ID='ADIABATIC',
COLOR='GRAY 80',
ADIABATIC=.TRUE./
&SURF ID='Surface01',
RGB=26,128,26,
HEAT_TRANSFER_COEFFICIENT=0.0,
VOLUME_FLOW=2.0/
&SURF ID='Surface02',
RGB=26,204,26,
HEAT_TRANSFER_COEFFICIENT=0.0,
VOLUME_FLOW=0.0,
PART_ID='Tracer',
DT_INSERT=0.1/

&OBST ID='Obstruction', XB=0.0,0.2,0.2,3.8,0.0,3.0, SURF_ID='ADIABATIC'/
&OBST ID='Obstruction', XB=0.0,6.0,0.0,0.2,0.0,3.0, SURF_ID='ADIABATIC'/
&OBST ID='Obstruction', XB=0.0,6.0,3.8,4.0,0.0,3.0, SURF_ID='ADIABATIC'/
&OBST ID='Obstruction', XB=5.8,6.0,0.2,3.8,0.0,3.0, SURF_ID='ADIABATIC'/

&HOLE ID='Hole', XB=5.8,6.0,1.4,2.8,1.0,2.0/

&VENT ID='Mesh Vent: MESH [XMAX]', SURF_ID='OPEN', XB=6.4,6.4,0.0,4.0,0.0,3.0/
&VENT ID='Mesh Vent: MESH [XMIN]', SURF_ID='OPEN', XB=0.0,0.0,0.0,4.0,0.0,3.0/
&VENT ID='Mesh Vent: MESH [YMAX]', SURF_ID='OPEN', XB=0.0,6.4,4.0,4.0,0.0,3.0/
&VENT ID='Mesh Vent: MESH [YMIN]', SURF_ID='OPEN', XB=0.0,6.4,0.0,0.0,0.0,3.0/
&VENT ID='Vent', SURF_ID='Surface01', XB=0.2,0.2,1.6,2.6,1.0,2.0/
&VENT ID='Vent02', SURF_ID='Surface02', XB=5.8,5.8,1.6,2.6,1.0,2.0/

&SLCF QUANTITY='PARTICLE FLUX X', PART_ID='Water', ID='CD', XB=0.0,2.0,0.0,2.0,0.0,2.0/

[mcgratta]

This is not a complete, functioning input file. Read the section in the User's Guide called Particle Insertion. Try adding the appropriate INIT line that would introduce a particle into the flow.