[FLASH-USERS] [EXT] Internal energy is not reaching statistical steady state in StirTurb (homogeneous isotropic turbulence) problem

Fri May 10 08:44:16 EDT 2024

Thanks a lot.

________________________________
From: Reyes, Adam <adam.reyes at rochester.edu>
Sent: Friday, May 10, 2024 2:40 PM
To: Alam Shadab TU Ilmenau
Cc: flash-users at flash.rochester.edu
Subject: Re: [EXT] [FLASH-USERS] Internal energy is not reaching statistical steady state in StirTurb (homogeneous isotropic turbulence) problem

There is a direcory "source/physics/sourceTerms/Cool” that has some stub implementations one could use to implement some kind of cooling function. Currently there is nothing implemented there but you could copy some of those files, namely “Cool.F90”, into your Simulation directory and implement whatever method you think is appropriate for what you want.

You might find it helpful to look at one of the other sourceTerm implementations to reference how to loop over the blocks and reset some of the data. "source/physics/sourceTerms/Polytrope/PolytropeMain/Polytrope.F90” might be good, as this is also included in the stirring turbulence simulations.
*********************************************
Adam Reyes

[FLASH.jpg]
Code Group Leader, Flash Center for Computational Science
Research Scientist, Dept. of Physics and Astronomy
University of Rochester
River Campus: Bausch and Lomb Hall, 369
500 Wilson Blvd. PO Box 270171, Rochester, NY 14627
Email adam.reyes at rochester.edu
Web https://flash.rochester.edu
 (he / him / his)
[FLASH-pride-sml.png]

*********************************************

On May 10, 2024, at 2:29 PM, Alam Shadab TU Ilmenau <shadab.alam at tu-ilmenau.de> wrote:

Hi Adam,
Thank you very much.
Actually, my work requires the system to be in a stationary state. For that, there is a need for me to add some internal energy removing mechanism in order to maintain the steady state, as has been done in

J. Wang, L.-P. Wang, Z. Xiao, Y. Shi, and S. Chen, A hybrid numerical simulation of isotropic compressible

turbulence, J. Comp. Phys. 229, 5257 (2010).

Please refer to page 38. The energy removal has also been done in my more studies.

As I am new to Flash, could you please help me in adding the energy removing term.

Thank you

Best regards,
Shadab

________________________________
From: Reyes, Adam <adam.reyes at rochester.edu>
Sent: Friday, May 10, 2024 12:50:38 PM
To: Alam Shadab TU Ilmenau
Cc: flash-users at flash.rochester.edu
Subject: Re: [FLASH-USERS] Internal energy is not reaching statistical steady state in StirTurb (homogeneous isotropic turbulence) problem

Hi Shadab,

The stirring is injecting kinetic energy into the simulation constantly throughout the simulation. This gets dissipated to internal energy through viscosity and has nowhere to go with a periodic box.
*********************************************
Adam Reyes

<FLASH.jpg>
Code Group Leader, Flash Center for Computational Science
Research Scientist, Dept. of Physics and Astronomy
University of Rochester
River Campus: Bausch and Lomb Hall, 369
500 Wilson Blvd. PO Box 270171, Rochester, NY 14627
Email adam.reyes at rochester.edu
Web https://flash.rochester.edu
 (he / him / his)
<FLASH-pride-sml.png>

*********************************************

On May 10, 2024, at 12:42 PM, Alam Shadab TU Ilmenau <shadab.alam at tu-ilmenau.de> wrote:

Hi,
I am simulating homogeneous isotropic turbulence with stir forcing. I am facing a challenge that the internal energy is not reaching to statistical steady state no matter how small the energy supply rate is. On the other hand, the kinetic energy has reached steady state. Following are the plots of these quantities:
<int_energy.png>
<kinetic_energy.png>
input parameters for this run are:
energy input - 1e-4 per mode (around 100 modes are stirred)
kinematic viscosity: 0.1
diffusivity: 0.1
grid: 128^3

I simulated the Stirturb problem for many other input parameters using split and unsplit methods, but I am getting the similar trend for the energies.

What am I missing because of which the internal energy is keep on increasing? Could anyone please help me with this?

Best regards,
Shadab
Technische Universität Ilmenau, Germany

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