[FLASH-USERS] Interpreting pressure behavior in the SinkRotatingCloudCore test problem

[Ryan Farber]

Hi Sean,

I'm not familiar with that problem so you'll hopefully get a more useful
answer from someone else. But until then, I have some thoughts below which
I hope might help.

First, this made me think of Jaehan Bae's work regarding the spiral density
wave instability. However, I believe that only happens when there's a
planet/object orbiting the (proto)star (what happens is that multiple gaps
in the disk appear despite there being only one object, implying that HLL
Tau's many gaps don't necessarily mean it has that many planets). I only
remember seeing movies of density but I would think the low density region
would also be low pressure).

Speaking of which, it might be useful to see density and temperature plots
as well to understand in which (or both) variable causes the low pressure
you're seeing.

Other thoughts:
Is there an analytic solution to your problem (or a simplified version of
it) to compare to? Absent that, you could try a different EOS solver. You
could also experiment with the hydro solver (if you're doing hydro, trying
the (un)split solver; different Riemann solver).

If all those look the same then I would think it's something physical. If
you have checkpoint files at 34,50 kyr then you can look at ACCX, ACCY,
ACCZ (check Flash.h if I spelled them right; I'm traveling currently) to
see if your low pressure region is in force balance, explaining it's
persistence. It may also help to consider the centrifugal, gravitational,
and pressure gradient forces individually.

I'm assuming SinkRotatingCloudCore uses self-gravity; is that in fact the
case? Does it use radiative cooling? If so, you might want to also try
turning cooling off to simplify things a bit.

Best,
Ryan



Sent from my iPhone
On May 25, 2019, at 11:59 AM, Lewis,Sean <scl63 at drexel.edu> wrote:

Hello all,



In my work towards modeling a protoplanetary disk, I have consistently
encountered an interesting behavior in gas pressure. Specifically, a region
of low pressure around the collapsed cold gas cloud that is generally about
10x lower than the pressure of the outer regions of the cloud as well as
the surrounding less-dense gas. I have attached a few .png files from the
out-of-the-box SinkRotatingCloudCore test problem to illustrate what I
mean. The images are taken at 34kyr and 50kyr taken looking down the
z-axis, and another 50kyr snapshot looking down the x-axis to see the
side-view of the forming disk.



How can this effect be interpreted? Something physical that’s expected?
Something numerical that is (un)expected? Initially, I thought that the
dense gas cloud was contracting towards its center of mass faster than the
surrounding halo gas, creating a vacuum of sorts. However, I have seen the
same effect in other simulations of mine where the dense gas is nearly
relaxed into a disk though to a lesser degree and the same effect is not
seen in plots of the gas density. This makes me think this could be an
artifact of the equation of state solver in some way.



With appreciation,



Sean Lewis

Drexel University





<pres34k.png>

<pres50k.png>

<pres50k_x.png>
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