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Search took 0.00 seconds. Search: Posts Made By: triple_r
Forum: Main CFD Forum December 15, 2013, 10:51
Replies: 32
Views: 4,232
Posted By triple_r
I see. So you are not using a spectral code to...

I see. So you are not using a spectral code to solve the problem, and just need an initial velocity for your non-sectral method? If that is the case, then you can use the sine relation I gave above...
Forum: Main CFD Forum December 15, 2013, 10:44
Replies: 32
Views: 4,232
Posted By triple_r
That is a work-around though. And it just...

That is a work-around though. And it just converts your spectral code to a central finite difference code.
Forum: Main CFD Forum December 15, 2013, 10:16
Replies: 32
Views: 4,232
Posted By triple_r
They are mathematically equal. So divergence...

They are mathematically equal. So divergence free-ness in physical space, means kx ux+ky uy+kz uz = 0 in the Fourier space. But this doesn't mean they are numerically the same. For example, if you...
Forum: Main CFD Forum October 24, 2013, 22:14
Replies: 32
Views: 4,232
Posted By triple_r
I don't remember such a difference. How are you...

I don't remember such a difference. How are you calculating the spectrum? At higher frequencies because of aliasing you might get a bit higher energy, but can't think of a reason for a difference in...
Forum: Main CFD Forum October 18, 2013, 10:44
Replies: 32
Views: 4,232
Posted By triple_r
Yeah, as I mentioned, you need to make sure the...

Yeah, as I mentioned, you need to make sure the frequency-domain field that you are generating is as MATLAB describes it "conjugate symmetric". Here is an octave code that I was able to dig from my...
Forum: Main CFD Forum October 18, 2013, 10:07
Replies: 32
Views: 4,232
Posted By triple_r
Hi, Multi-dimensional IFFT can be a real...

Hi,

Multi-dimensional IFFT can be a real headache sometimes, specially when you are generating values in frequency domain and you are hoping to get a real-valued function in physical space.

I'm...
Forum: Main CFD Forum October 16, 2013, 09:53
Replies: 32
Views: 4,232
Posted By triple_r
Why two-dimensional? Turbulence is intrinsically...

Why two-dimensional? Turbulence is intrinsically three-dimensional.

Anyhow, if you want a 2D initial field, you can either generate a 3D field and apply any averaging operator on the third...
Forum: Main CFD Forum May 7, 2013, 10:36
Replies: 32
Views: 4,232
Posted By triple_r
I don't know if you are still interested in this...

I don't know if you are still interested in this or not, but you can find an initial velocity field for homogenous turbulence in the following paper:

Numerical Experiments in Homogeneous...
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