[Nek5000-users] RB convection with high Rayleigh numbers

[nek5000-users at lists.mcs.anl.gov]

Hi Mani,

I've not tried to go this high yet, but there are several std
techniques to pushing the envelope.

First, you should try to get an estimate of your expected resolution
requirements at the target Ra.   Then, guess that you might want to
run that simulation at say, lx1=10 or 12; and build the corresponding
mesh (number of elements in x and y); but start the compuation at
much lower Ra, with lx1=4, say.

Then work your way up in Ra, say by a factor of 10 in each successive
run, while also increasing lx1 as needed.

Note that for the flow in a box, you might find it faster to use
the fast tensor-product solver for the pressure, if using the Pn-Pn-2
method --- this is not always the case, but for some very difficult
problems (e.g., highly refined meshes), it does work better.

Paul


On Sat, 15 May 2010, nek5000-users at lists.mcs.anl.gov wrote:

> Hi,
>
>    I'm trying to simulate RB convection in a 2D box of aspect ratio 2:1. I'd 
> like to simulate cases with Rayleigh numbers of the order of 10^7 - 10^8. But 
> I'm barely able to do 10^5 and that too with a time step of 10^-6. For the 
> mesh I took 8 spectral elements in the x direction and 4 spectral elements in 
> the y direction with 48 points within each of them. Is there any way one can 
> reach higher Ra numbers?
>
> Regards,
> Mani chandra
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