TAGGED: fluent, Sand-grain-Roughness, turbulent-flow, wall-roughness
January 28, 2023 at 11:28 amrodriguezSubscriber
I have to make two simulations of a 2D elbow. One with roughness and one smooth. I am told to make two meshes, one for smooth and one for the rough surface, which I don't understand.
I read about the logarithmic law shifting down in the u+ y+ chart due to the higher wall shear, and saw the problem with the connection of that logarithmic law with the buffer region and the viscous sublayer region.
Based on that, I understand the first cell should always be in the log region, right?. That makes the roughness not being available in the KE model with Enhance Wall Treatment understandable.
Now, if I use SSTkw or the RKE with Scalable Wall Function (recommended wall function), and I am in the log law region with the first cell in the smooth case, why might the mesh not be good enough for the rough case? The only possibility I see is that due to the wall shear increase the y+ will increase and go out of the chart, so to say, being away fromt the log law too. Is that thinking correct?
On top of that, I have seen the "virtual wall shifting" approach that states that y⁺=y⁺ + Kr⁺/2. Now, I don't understand what the difference between the y⁺ on the left side of the equation and the one on the right side is. Is the one at the left the one used by Fluent to calculate the wall shear at the wall and the other one the one with the real y of the mesh?? Also, using wall functions makes it more intuitive, but, what is in general going on in the SSTkw model, where no wall functions apply?
Any help would to help me understand. The Fluent help didn't really help...
Thanks and regards.
January 30, 2023 at 4:19 pmRobAnsys Employee
There are a couple of courses on turbulence and near wall effects, look under Learning on here.
The wall roughness models are there to work with the wall functions & turbulence models. You then have to balance the near wall cell height with the roughness: how valid is the assumption if the near wall cell is smaller than the roughness height? The manual may or may not clarify the settings, but as staff we're only able to point you at that. I think the topic is covered in more depth in the Ansys Learning Hub, but you'd need a subscription to access that - have you asked whoever set the exercise for more information?
- You must be logged in to reply to this topic.
Boost Ansys Fluent Simulations with AWS
Computational Fluid Dynamics (CFD) helps engineers design products in which the flow of fluid components is a significant challenge. These different use cases often require large complex models to solve on a traditional workstation. Click here to join this event to learn how to leverage Ansys Fluids on the cloud, thanks to Ansys Gateway powered by AWS.
Earth Rescue – An Ansys Online Series
The climate crisis is here. But so is the human ingenuity to fight it. Earth Rescue reveals what visionary companies are doing today to engineer radical new ideas in the fight against climate change. Click here to watch the first episode.
Subscribe to the Ansys Blog to get great new content about the power of simulation delivered right to your email on a weekly basis. With content from Ansys experts, partners and customers you will learn about product development advances, thought leadership and trends and tips to better use Ansys tools. Sign up here.
- Suppress Fluent to open with GUI while performing in journal file
- Floating point exception in Fluent
- What are the differences between CFX and Fluent?
- Heat transfer coefficient
- Getting graph and tabular data from result in workbench mechanical
- The solver failed with a non-zero exit code of : 2
- Difference between K-epsilon and K-omega Turbulence Model
- Time Step Size and Courant Number
- Mesh Interfaces in ANSYS FLUENT
- error: Received signal SIGSEGV
© 2023 Copyright ANSYS, Inc. All rights reserved.