[huangxianbei]

Originally Posted by sbaffini

Dear Huang,

a very rough estimate for your case leads me to 14 GBytes of memory required when using the typical number N=16 for the local polynomial degree (or number of points, i don't remember now but it is ininfluential). Indeed, roughly speaking:

N=16 -> E = (192/16)*(128/16)*(160/16)

you have to compare the same case with the same number of degrees of freedom.

Yes,you are right. So this degree of memory require can be easily reached. However, I found the user-manual is quite poor as said on the official site
I want to do a channel flow DNS using Nek5000, if you have more documents or something helpful to learn this code, I'll be very very thankful

[sbaffini]

Unfortunately, that's all i got to learn Nek5000. However, at least one of the manuals is not that bad and you can use the examples to start using it. For example, there is a channel flow example which should be perfect for you. Obviously, as i said, this i snothing close to a commercial code anymore, and you have to look at the code to know what the subroutines do. However, compared to large codes like OpenFOAM, i found it very simple to understand, considering that you don't need to manage the core part of the code.

[huangxianbei]

Originally Posted by sbaffini

Unfortunately, that's all i got to learn Nek5000. However, at least one of the manuals is not that bad and you can use the examples to start using it. For example, there is a channel flow example which should be perfect for you. Obviously, as i said, this i snothing close to a commercial code anymore, and you have to look at the code to know what the subroutines do. However, compared to large codes like OpenFOAM, i found it very simple to understand, considering that you don't need to manage the core part of the code.

Thank you. There exactly exists a channel flow example. Although the code is much smaller than OF, it's not so easy to learn for me I think I need more time to go through the code.

[sbaffini]

Originally Posted by cfdnewbie

I would say at least a factor of 6 or so. From dissipation / dispersion analysis, I seem to remember that O1 or O2 FV schemes took somewhere between 10 and 20 cells to resolve a wave properly, where spectral codes need 2....
We are running spectral element codes with high N (8th order and above), and with that you can get down to 4 PPW, so that would be a factor of 2 compared to spectral. Low order FV is a totally different game....

I am not sure about that, at least not in practice. My experience is that with Fluent, and the same number of DOF as in a spectral code, the FV solution affects only the upper third of the resolved wavenumbers. However, i'm talking about the channel flow at Re_tau = 180, hence the energy transfer (toward the smallest scales) at such low Re number might be not enough vigorous to evidence all the numerical artifacts.

[lovecraft22]

Also PowerFLOW can do DNS.
https://www.exa.com