[Nek5000-users] turbChannel: Questions about targetCFL and dealiasing

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

if you use the characteristic scheme that is. In the other case (i.e. 
ifchar turned off), it is a classic IMEX scheme with target CFL of 0.5.

I wonder, have there been any comparisons between the two schemes for 
standard cases like turbulent channel flow?

On 2018-02-11 11:49, nek5000-users at lists.mcs.anl.gov wrote:
> The code implements OIFS (operator integrator splitting factor) not an 
> implicit fractional step method! A convection problem is integrated in 
> substeps with RK4. For a targetCFL of 3.5 you need at least two substeps 
> to be stable. You can increase the targetCFL even further depending on 
> the desired accuracy.  If this helps to lower time to solution depends 
> on the cost of the pressure solve.
> 
> If you want to run the solver as fast as possible turn off dealiasing. 
> In all other cases turn it on (lxd has to have the right size e.g. 3/2 
> rule).
> 
> On 10 Feb 2018, at 18:28, "nek5000-users at lists.mcs.anl.gov 
> <mailto:nek5000-users at lists.mcs.anl.gov>" 
> <nek5000-users at lists.mcs.anl.gov 
> <mailto:nek5000-users at lists.mcs.anl.gov>> wrote:
>>
>> Dear Nek users,
>>
>> I have some fundamental questions in terms of CFL and dealiasing in 
>> the example of turbChannel. In the .par file, I noticed that the 
>> default setting of targetCFL is as high as 3.5, which really makes the 
>> code run very fast. But, typically, this CFL value is around 0.5 using 
>> implicit fractional time-step approach based on the FV method. Why CFL 
>> could be this high here while not compromising the stability? Is it 
>> because of the spectral element method?
>>
>> And Could you also please tell me when shall I turn on or off dealiasing?
>>
>> Regards,
>>
>> Emily
>>
>> _______________________________________________
>>
>> Nek5000-users mailing list
>>
>> Nek5000-users at lists.mcs.anl.gov <mailto:Nek5000-users at lists.mcs.anl.gov>
>>
>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>>
> 
> 
> _______________________________________________
> Nek5000-users mailing list
> Nek5000-users at lists.mcs.anl.gov
> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>