[aspect-devel] questions about heat flux output

[Wolfgang Bangerth]

Paul,

> I'm new to ASPECT, and I've been running the cookbook parameter files to
> get started. I'm sure this is very basic, but while running the
> shell_simple_2d.prm I noticed that the heat flux values through the
> inner and outer boundaries are only in the megawatts range, and the
> inner boundary even has a negative value, and this appears at every time
> step. The final animation of the temperature parameter from the
> solutions files look completely normal, though. In the case of the
> shell_simple_2d.prm, the inner and outer boundaries have fixed
> temperatures, 4273K and 973K, respectively, and the inner boundary is a
> rigid surface.
>
>
> My question is; what do these values actually represent? They seem too
> small (and the negative values seem strange) to be the actual heat flux
> values. Are these perturbation values, or are the units not what I think
> they are?

The heat fluxes are in *outward* direction. So, at the inner boundary, a 
negative heat flux means that a negative amount of thermal energy is 
moving out of the mantle into the core -- or, put differently, energy is 
moving from the core into the mantle. The sign is correct.

As for the values: It's a 2d model, but you compare the numbers to what 
you know about the 3d earth. You cannot expect them to match. (It is 
also worth mentioning that the heat flux greatly increases after a while 
once the convection starts going; I don't know whether you looked at the 
numbers only at the beginning of the simulation when things are still 
starting, or after a while when stuff is vigorously moving around.)

Best
  Wolfgang


-- 
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Wolfgang Bangerth          email:                 bangerth at colostate.edu
                            www: http://www.math.colostate.edu/~bangerth/