Set the following scales in physics.data:

lscale	3.08 e+18 cm
rscale	2.02 e-16 g/cm3
tempscale	1 K

From that initialized an ambient object with the following density and pressure,

ambient%rho=2.03d-16/rscale
ambient%pressure=(rhoOut/rscale)*(tempOut/tempscale)

Have my grid running from, gxbounds= -.0068 -.0068 0 .0068 .0068

I ran the sim to frame 0 to get the timescale from scales.data.

I used this to get the tsim=tdiff in computational units,

tsim=2.074e+6s/!338402526430554s = 6.13e-9

Next, I calculated the energy injection rate using the luminosity of a FHSC:

L=3.9e+29 erg s^-1
Lscale=Pscale*(lscale)³/timescale=1.46*10³³
L(cu)=2.67 e-4

Next came scaling the opacities.

The code takes specific opacity (this is in cm²/g), and then asks whether it should be constant, or multiplied by density (or temperature) to some power. I set it to be a power law scaling.

tpow=0
dpow=1

so that,

opacity=kappa*rho

I scaled the planck and rosseland opacities into computational units by:

kappa_r=0.23*mscale/(lscale)²=144.07
kappa_p=.4*mscale/(lscale)²=250.56

Radiation was set to 'diffusion and energy exchange only', rad limiter was set to 'diffusion limit'.

This all seems right to me, so then here are the results.

Run 1

de/dt=7.73246e+21

I calculated the diffusion time assuming the scale-height was = box radius (which also equals the mean free path). Because of this, I thought I was in the optically thick limit everywhere in my box, so chose the flux limiter to be constant… =1/3 in the data file. From this, I calculate the diffusion time to be 24 days. Is this a good estimate?

A diffusion wave is the time is take a signal to spread out over some length scale. Imagine a delta source spreading out. When its width equals its half max, is roughly a diffusion time.

Here is Erad over time:

Why do the wings leave the grid faster than the speed of light?

This has to do with the fact I am not 'limiting' the diffusion through the limiter, when I should be doing that. Instead, I am using a constant lambda, which I thought at the time might be appropriate. However, as this plot of R shows, that is not the case:

In some regions, the limiter should be smaller than 3, so as to limit the diffusion wave in optically thin regions — so that it is below the speed of light. Because that is not happening, I am getting superluminal signal. (This should be fixed by tracking lambda dynamically through the grid).

Here is a movie​ of R_limiter.

And an image of the inverse scale height:

Since, the scale height is not the same as the mean free path in actuality, getting unphysical diffusion speeds on the wings. However, given this does not represent a diffusion time, not sure it effects my prediction for a diffusion time.

Here is a movie of the temperatures over time:

Run 2

Same de/dt, but now increasing lambda by factor of 10 (this decreases mean free path by 10x, and thus increases tdiff by 10x).

Run 3

Same de/dt but now with higher lambda

Run 4

Run 1 at lower resolution

Run 5

Run 1 with dynamic lambda

Run 6

Run 3 with dynamic lambda

Run 7

Run 1 with lower density (do we see the temperature /coupling change ?)