[FLASH-USERS] courant factor

[Ryan Farber]

Hi Riccardo,

In the directory you compiled the code (e.g., "object") try "ls -lh
*computeDt*"
That should show you all the possible timestep limitations (and note that
Driver_computeDt calls the other routines).

That may also help you understand why you need the cfl that low; diffusion
for example scales Delta_t as Delta_x**-2; I'm not sure about the
restrictions for some of the turbulence and other FLASH physics.

Best,
--------
Ryan

On Thu, Apr 27, 2017 at 5:57 AM, Riccardo Ciolfi <
riccardo.ciolfi at oapd.inaf.it> wrote:

>
>  Dear all,
>
> I am trying to understand the definition of the variable cfl. Does it
> correspond to the courant factor Delta_t/Delta_x * v_max?
> Is this the same at all levels, so that Delta_t is reduced by a facotor of
> 2 together with Delta_x when moving to the next refinement level? Is there
> a simple way to enforce it?
>
> I am using FLASH4.4 and for 1D hydro simulations I adopted the suggested
> clf=0.8 without any problem. When I move to 2D I cannot run unless I put
> cfl as low as 0.1. Is this expected? For coordinates with Delta_x=Delta_y,
> shouldn't be sufficient to reduce the courant factor by a factor of sqrt(2)?
>
> Thank you very much for the attention!
>
>  Best,
>  Riccardo Ciolfi
>
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