[Nek5000-users] [*] Re: RB convection with high Rayleigh numbers

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

Hi Paul,

     Thanks for the reply. I have a doubt whether one should increase 
the polynomial order or the number of elements with a fixed order for 
this case. As I understand from your illustration of the rotating cone 
case, increasing the polynomial order leads to a much better solution 
than with the same number of points generated using more elements with a 
lower order polynomial.

Also how do I use the fast tensor-product solver? Is there some flag 
that I need to turn on?

Regards,
Mani chandra
On 05/15/2010 09:05 PM, nek5000-users at lists.mcs.anl.gov wrote:
>
> 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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