Gas field in specified area, alternate...

But wait, there's more!
Another approach I've found on the webs, is to make a Gas Match Field, which makes a new field based on some other value.. eg. Density or Temperature.
You can actually specify a Density that is not the Pyro-sim's density, by using a Source Volume (turns out they don't always have to go into the last input). Point that to your custom volume
Finally, set the control mask to your new field.

All three of these nodes should be plugged into a single merge, which then goes into the Velocity Update of the pyro solver. (or the advect...)

I think this approach might be more flexible, if you are using it to refer to an internal pyro-value like Density or Temp?

Another approach I've seen skips the external source volume and copies the Temperature from the pyro solver itself. They use Gas Match to make a field which is "equal" in size/type to Temperature,
Next they use a gas calculate node to copy the Temperature to the custom field,

Finally, They  use a gas field wrangle to fiddle with the newly created field. Normalise values, or do whatever..

They use the custom field as a mask for dissipate & turb.
Quite a neat way to mess around with the temperature.

Gas field only in specified area. Stolen from the Sidefx site

1.  In the DOP network, add a SOP Scalar Field node after the Pyro object.
   
   • Turn on Use SOP Dimensions.
   • Set the SOP path to the path of the fog volume object (for example /obj/mask_object). Make sure Use Object Transform is on.
   • Set the Data Name to something indicating the purpose of this field, for example NoiseMask.
   This attaches the fog volume as field data on the Pyro object with the given name.
   
2. Create a Gas Turbulence node and connect it to the fourth ("Advection") input of the Pyro solver.
   
   • On the Bindings tab, set the Density Field to the name of the mask data, for example NoiseMask. The effect of the node is multiplied by the value of this field.
   • Use the controls on the Turbulence Settings tab to control the amount of turbulence added.
     
     
     
     
     Important thing to note - by default the control field will not be 100% in control.. You'll see some "leakage" of turbulence. This is because the Control Influence is set to 0.5 by default.. Whack it up to 1, and maybe tweak the remap-graph to fine tune the effect of the turb/whatever.

Pyro UPRES

Setup a Pyro as you would normally..This will be your low res sim. In a Geo sop somewhere, make a DopIO node and choose the pyro preset to make sure you're importing all the required fields from the low res sim. You could file cache this out..

Then..make a new Dop network. Inside this, create a smoke object and plug it into a Gas Upres node.
Point the Gas Upres node's Initial Data/Low Res Sop Path to a DopIO node you made earlier. Alternatively if you've cached it out to VDBs or bgeo.sc's you can switch the source to "file" and point it to that cache.


I've found that putting a copy of your low res sim's Source Volume helps a lot. Plug that into the last input of the Gas Upres. Switch it's Velocity setting to COPY, since you'll want to copy it from the lowres sim.

You might have to play with the smoke object's initial size settings, so that it encompasses your entire sim size. Oh - and change the division size to your desire resolution..we are upres-ing after all.

Mess around with extra dissipation or turbulence in the Gas Upres node...

That should be it.