# Pyro: Smoke

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Hi,

How do I make my smoke go one way or another? I mean I don't want to play with cooling rate, temperature diffusion and byuancy lift.

Is't there just a single simple attribute temperature? Like in fume? you want to go up do you take + values, you want to go down to you take - values.

But in pyro i see it is too much complicated.

What I need is my smoke to rise just a little bit. But what I get is that it's going down at the begginging and then it rises.

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I am a little confused on what your asking here. But form what I understand you could add some velocity from the source node so it will go up from the start. Then it should go up right at the beggining.

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The buoyancy direction is what makes your smoke go up based on its temperature. It's exactly the same in Fume. If you source negative temperature values, your smoke will go down. I've attached a very simple scene file just to prove it.

You should also be mindful of your velocity field in case you're sourcing one as well. If I had to guess, I'd that is the culprit behind your problems.

If you have the time, please follow along this tutorial - don't just watch it  :

edit: derp, I forgot to answer the last part of your post - if you want your smoke to rise slowly, you can either reduce the Buoyancy Lift on the Pyro solver or scale down the temperature field in the Source DOP. Technically speaking there's nothing stopping you from doing that in SOPs with a Volume VOP either - just Bind the temperature and multiply it by 0.5

smokeSim.hipnc

Edited by Georgie

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The buoyancy direction is what makes your smoke go up based on its temperature

And this part should be true, but it is not. And this confuses me. Both [0,1,0] and [0,-1,0] buyancy directions have the same resault.

Here is a scene as a proof

byuancy.hip

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I took a look at your file.  A few things I notice:

there is no temperature being sourced into the simulation, therefore bouyancy wont work.  In H13 and before, the source volume would by default, use density to source into temperature if a temperature source field wasnt present.  Now in H14, you must explicity tell the source volume to use the source density field to source into temperature as well. Source volume node > SOP to DOP bindings tab.

You also need to account for the gravity in the sim.  Currently it's force is greater than the bouyancy force, so the smoke will still go downwards.

byuancy1.hip

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You are not sourcing any temperature in the Fluid Source SOP. Go to the Container Settings tab and set it to Source Fuel (just to reset the node) and then back to Source Smoke -> it's weird, I know but that's how it rolls.

Additionally, the Gravity is affecting the fluid. Also, you've set the Density scale on the Fluid Source to 10. You may need to scale up the temperature quite a bit as well. Maybe even increase the buoyancy lift to 10 or 20. That's probably not the best way to handle the situation but hey, I'm just trying to help ;p

Maybe someone more knowledgeable will join the discussion.

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Thanks! That explains everything!

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