Color + divergence in smoke sims?

[bloomendale]

Hi.

I'm curious how fields get affected by adding divergence (i'm not asking about projection stage or velocity field)? Adding it will add density, but what about my additional scalar or vector fields (eg Cd)?

How can i control values in color (vector) field using divergence (or combustion model, which is the same in this aspect),

Cause while density is being added due to divergence, other fields stay the same and just advected by velocity (so the same amount of my color field vs bigger amount of density)?

Thanks in advance.

[Peter Quint]

I am not sure I completely get your question, but here is an explanation that might help.

Divergence in effect acts as a force. If I recall right where you have a positive value in your divergence field the gas / smoke / fluid will expand outward from that point, while if the value is negative then the fluid will be attracted in towards that point. It is the advection by velocity step that actually achieves this. So it doesn't directly affect density, though clearly it may do over time. Typically you have diversity at the source of an explosion, for example, to force the smoke / fire cloud outwards, but you are probably also emitting / sourcing density at that point also, so the density at the centre of the divergence might not change.

You can advect any field you like using exactly the same method as the solver uses for the density. If you use the add field tool from the shelf then it will set up not only your field but the advection by velocity for your field, so that your colour field, for example will be affected in the same way by divergence as the main smoke or fire.