The Fluid Flow Simulation is incorrectly wired. It should have the two
density advection objects take their velocity from the feedback (last
frame) rather than the current velocity advection object. Since that
velocity advection hasn't been "projected" yet, it will not be mass-
conserving and will cause excess diffusion of the density.
I added a bug report for this, but if you use the 2D Fluid patch, you
might want to repair it yourself. Just connect the Bypass velocity
output to the sourceImage input of each Advect Velocity object. It
doesn't make a huge difference, but it appears to me that the density
is diffusing more slowly this way, and the vortices are more apparent.
This algorithm closely resembles Jos Stam's "Stable Fluids" algorithm,
but without any diffusion operations. You can DL a PDF of Stam's paper
from here:
<http://www.dgp.toronto.edu/people/stam/reality/Research/pdf/GDC03.pdf>
- Stoney
--
Stonewall Ballard
[email protected] http://stoney.sb.org/
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