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RANS Grid Sensitivity Divergence on LES Grid

Posted August 31, 2020 at 17:29 by MikeBravo

Reference on not changing y+ while doing a grid sensitivity study:

Quote:
Originally Posted by sbaffini View Post
Indeed, if y+ =4 is relative to the finest grid, it is confirmed to be a wall function problem. I can't double check now, but I'm pretty sure that the k-omega sst model in CFX uses an all y+ wall function, which means that a wall function is always active. While, in theory, such wall functions should be insensitive to the specific y+ value, they are not perfect and your case is very far from the typical wall function
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Old

Y+ value for Large Eddy Simulation

Posted August 31, 2020 at 15:35 by MikeBravo

Explanation of Y+ as it relates to viscous sublayer and advection scheme:

Quote:
Originally Posted by cfdnewbie View Post
yes, at least in the viscous sublayer. The size of your grid cell (or the number of points per unit length) determine the smallest scale you can catch on a given grid. From information theory, the Nyquist theorem tells us that we need at least 2 points per wavelength to represent a frequency (we need to be able to detect the sign change). However, 2 points per wavelength is just for Fourier-type approximations.
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Old

Rans

Posted August 31, 2020 at 15:08 by MikeBravo

Quote:
Originally Posted by vinerm View Post
That's a wrong notion that RANS or EVM models are introduced to get faster results or are expected to be used with coarse mesh. There is no such assumption behind development of these models. The only assumption in EVM is that the turbulence is isotropic and non-EVM RANS, such as, RSM don't even have that assumption.

And when it comes to wall treatment, it is not directly linked with turbulence model; even LES requires wall treatment. y^+ is a non-dimensional (Reynolds) number and
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Rating: 2 votes, 5.00 average.

What I've done in the past years and may need someone else to pick it back up

Posted August 18, 2020 at 17:11 by wyldckat
Updated August 22, 2020 at 06:13 by wyldckat

This is a blog post aimed to pass on the baton of the work I've done in the past to anyone who wants to pick it back up partially or completely, which I was still doing (or trying to do) until Hanging my volunteer gloves and moving to a new phase of my life.


This blog post could potentially be edited as time goes on and I remember about things I've done in the past and which should be picked up by someone else:
  1. Generating version template pages and logos for said versions
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Rating: 2 votes, 5.00 average.

Hanging my volunteer gloves and moving to a new phase of my life

Posted August 18, 2020 at 17:10 by wyldckat
Updated August 19, 2020 at 06:47 by wyldckat

TL;DR: As of 2020, I can only help during office hours, at work, if paid and/or affects our projects, namely what we use in OpenFOAM itself and blueCFD-Core.

Full post:
So nearly 2 years after my blog post Why I contribute to the OpenFOAM forum(s), wiki(s) and the public community, I'm writing this blog post you are reading now.

My last 3 thread posts at the forums in CFD-Online this year, were on May 7th, February 27th and January 20th. And before that, it was 10...
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