PyFR setup and error

54 views
Skip to first unread message

Amir Hossein Jafari Matin

unread,
Nov 19, 2020, 7:39:15 AM11/19/20
to PyFR Mailing List
Dear PyFR developers,

I am writing my master thesis using pyfr to simulate the flow over a turbine cascade similar to T106c test case used in "F. D. Witherden and A. Jameson Impact of Number Representation for High-Order Implicit Large-Eddy Simulations" paper. However I have some questions about the setup and an error I am facing at:

1.       The Error “Minimum sized time step rejected”, does it mean, that the simulation diverges?  Sometimes the simulation goes on, when I just restart the simulation from the last solution, however sometimes I get the error at one specific time. I also tried to limit the time step using dt-max, but it did not work. If I turn off the PI controller, I get NaN values instead. I should mention that I have relatively fine mesh (comparing with your T106c test case). Do you have any suggestions, how I can prevent this error?

2.       Do I need to use anti-ailiasing just for Polynomial orders higher than 2? Did you use it for the T106c case at P2 and Re=80000?

3.       In my understanding the reference Reynolds number is not defined in pyfr in case of non-dimensionalaizing, therefore we have to eliminate it by choosing a specific reference dynamic viscosity, namely Mu_t0 = rho_t0 * a_t0 * Lc (Mu_t0 : Reference dynamic viscosity, rho_t0 : Reference density, Lc : Reference Lenght). So that the reference Reynolds-number would be 1. Is that correct?


Regards,

Amir Matin


 

Freddie Witherden

unread,
Nov 19, 2020, 9:48:15 AM11/19/20
to pyfrmai...@googlegroups.com
Hi Amir,

On 19/11/2020 06:39, Amir Hossein Jafari Matin wrote:
> 1. The Error “Minimum sized time step rejected”, does it mean, that the
> simulation diverges?  Sometimes the simulation goes on, when I just
> restart the simulation from the last solution, however sometimes I get
> the error at one specific time. I also tried to limit the time step
> using dt-max, but it did not work. If I turn off the PI controller, I
> get NaN values instead. I should mention that I have relatively fine
> mesh (comparing with your T106c test case). Do you have any suggestions,
> how I can prevent this error?

This typically means that the simulation is diverging. There are many
possible reasons for this; including your mesh and start-up procedure.

> 2. Do I need to use anti-ailiasing just for Polynomial orders higher
> than 2? Did you use it for the T106c case at P2 and Re=80000?

Here it very much depends on the mesh, polynomial order, and Reynolds
number. For this particular case I did not run with anti-aliasing,
however I did need to be careful with how I started the simulation
(running at p = 1 for a period of time before restarting at p = 2).

> 3. In my understanding the reference Reynolds number is not defined in
> pyfr in case of non-dimensionalaizing, therefore we have to eliminate it
> by choosing a specific reference dynamic viscosity, namely Mu_t0 =
> rho_t0 * a_t0 * Lc (Mu_t0 : Reference dynamic viscosity, rho_t0 :
> Reference density, Lc : Reference Lenght). So that the reference
> Reynolds-number would be 1. Is that correct?

The Reynolds number is typically fixed by changing the viscosity, yes.

Regards, Freddie.

Amir Hossein Jafari Matin

unread,
Nov 19, 2020, 3:55:29 PM11/19/20
to PyFR Mailing List
Hi Freddie,

thanks for your kind reply.

Regards
Amir

Reply all
Reply to author
Forward
0 new messages