[FLASH-USERS] Question regarding velocity update in Stir.F90

[Christoph Federrath]

Dear Shadab,

I implemented this. The reason for subtracting the bulk momentum is that we normally use continuous turbulence driving in periodic box simulations, such that the gas remains in the zero-momentum rest frame. It is usually a tiny correction, so switching this off mostly likely wouldn’t matter, but I chose to do it to make the momentum perfectly zero in x, y, z. If you have a different application in mind that would require you to keep the momentum, I’d be happy to chat further or make this a user parameter, for instance. Btw: the most recent TurbGen code is available here (which includes some extra features, such as automatic amplitude adjustment, etc.):
https://www.mso.anu.edu.au/~chfeder/codes/turbgen/turbgen.html

Best regards,
Christoph

—
Professor Christoph Federrath
Research School of Astronomy & Astrophysics
Australian National University, Canberra, ACT, Australia
Tel: +61-2-6125-0217 <tel:+61-2-6125-0217>
Web: https://www.mso.anu.edu.au/~chfeder

> On 13 May 2024, at 10:08 PM, Alam Shadab TU Ilmenau <shadab.alam at tu-ilmenau.de> wrote:
> 
> Hi,
> 
> I have a query about why the 'momentum/mass' is subtracted during the velocity update in the forcing unit. Here's the snippet from Stir.F90 for reference.
> 
> <Screenshot from 2024-05-13 13-51-41.png>
> Could anyone please clarify this?
> 
> Best regards,
> Shadab
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