[mesa-users] accretion

[David Arnett]

I think (actually I am quite sure) I agree with Ben.

Some further thoughts:

There are two different time scales which are important here. One is the
"entrainment: time scale which is how fast the turbulence is eating into
the stable regions at the boundary (this tends to be slow), and the other
is the "cycle" time scale, which is how fast the integral scale convection
takes to move matter from the top to the bottom (or vice versa) of the
turbulent region. If we are lucky we can implicitly solve the cycle time
scale, and increase the delta t allowed for MESA stability.

In a turbulent cascade the largest scale (the "integral" scale) is the
dominant transport mode and probably the physically relevant CFL
(causality) time scale. This is a global feature of the turbulent layer,
not of the zoning, and should be much larger than the CFL for the smallest
zone. Have hope Bill, the presence of fluctuations may not mean that we
have to resolve them in time, just that we have to approximate their
average behavior.

Dave


-- 
David Arnett
Regents Professor
Steward Observatory
University of Arizona

Facts are stubborn, but statistics are more pliable.  Mark Twain
Facts do not cease to exist because they are ignored.  Aldous Huxley
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