How to select properly ac-zeta?

[Giulio Ortali]

Hello everyone,

I am still running the case I was mentioning in the last 2 post on this mailing list, i.e. high reynolds (3e6) 2D incompressible flow over the ls417.

I have problems since the results, in particular the k coming out of the results, are quite different from the one computed using the RANS, almost two orders of magnitude higher.

I was thinking about the possible reasons for this and I was thinking that maybe using a ac-zeta lower than the standard 2.5 would give different results, maybe similar to the RANS. Could this be the case? What is the rationale behing the choice of zeta? I understood that lower zeta bring to "more incompressible" flows, but what are the downsides of chosing a low zeta? Also, what could be other trials to do in order to obtain k similar to the RANS?

I attach the ini file and the mesh.

Thank you in advance,

Giulio

[Niki Loppi]

Hi Giulio,

Thanks for your interest.

There are multiple suggestions in literature for selection of ac-zeta. I suggest using ac-zeta=3*Umax, where Umax is  approximately the maximum local velocity magnitude in the domain. Selection of ac-zeta shouldn't have big effect on the results but it can considerably affect the convergence rates.

Turbulence at high Re is highly three dimensional and hence cannot be resolved in 2D. That may be one of the reasons for the result mismatch.

Cheers,

Niki

On 22/01/20 15:20, Giulio Ortali wrote:

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