November 12, 2020 at 2:07 pmshehab GamrahSubscriber
I modelled a symmetric geometry with a velocity inlet and two identical pressure outlets, and my problem is I expected flow to be symmetric as model is symmetric but actually the flow becomes asymmetric and depends on Mesh size. In the 2 figures below when I altered the mesh size, the velocity pattern shifted from the upwards channel to the downwards channel hence I would like to know the mesh size shifts the flow pattern and also how can I obtain a symmetrical solutionNovember 12, 2020 at 4:22 pmRobForum ModeratorSimple answer is you can't. Read up on flow separation, Coanda effect, unconstrained jets and pitchfork bifurcation. You may also want to have a look at how fluidic devices work, mainly the switches. The above results look about as I'd expect, and if you ignore which outlet is used the flow looks pretty much identical in both cases. nNovember 12, 2020 at 5:29 pmshehab GamrahSubscriberThanks Mr RobnBut what seems confusing is that I modelled same geometry but just added a porous medium in the ellipse shaped part and the same boundary conditions and the flow became symmetrical for that case. So I have got 2 questions:n1) Would flow pattern be symmetrical in real life for the previously attached cases or does the coanda effect happen not in only for CFD but in real life.n2) Why is the same case with a porous medium behave in a syemmetric flow manner and the other cases attached above didn't nnNovember 12, 2020 at 5:57 pmDrAmineAnsys EmployeeCoanda is real and happens outside CFD too.nNovember 12, 2020 at 5:58 pmDrAmineAnsys EmployeeWith porous media you are adding resistance and so a sort of smoothing of velocity might happennNovember 13, 2020 at 2:05 pmRobForum ModeratorIn the porous case you don't have much (if any) flow in the chamber. Jet hits the surface and then spreads so there's nowhere for it to go to create the asymmetry. nNovember 18, 2020 at 1:44 amshehab GamrahSubscriberThanks for all the help. I just wanted to raise another question to close the topic. I modelled the same geometry in 3d and done the simulation with same boundary conditions but the flow seems to be symmetrical for the 3d model under the same inlet velocity. so does coanda not occur for 3d models or should I increase velocity for 3d case and the flow would become asymmetrical.nnNovember 18, 2020 at 9:27 amDrAmineAnsys EmployeeCoanda occurs in 3D, 2D and 1D. You can even run transient and create a mean of flow to check if it is chaning.nNovember 18, 2020 at 11:24 amRobForum ModeratorThat jet looks to diffuse quite quickly, how well resolved is it? Fluidic switches take advantage of this phenomena, and if you nudge the jet one way or the other you can control the outcome. In my opinion the best use of this was in the US:they had a rocket powered shopping trolley at (I think, it's been a while since I worked in this field) Harry Diamond Labs in the US. nNovember 18, 2020 at 3:55 pmshehab GamrahSubscriberDear Mr RobnSo i've done a mesh convergence study on the case and still the flow is symmetric and not similar to the 2d case. Is there any way I can resolve this issue to obtain an asymmetric flow similar to the 2d case.nNovember 18, 2020 at 4:04 pmRobForum ModeratorPlease can you post some images? Velocity & pressure on the mid plane same view as before. Zoom in around the expansion area. nNovember 18, 2020 at 4:13 pmNovember 18, 2020 at 4:26 pmRobForum ModeratorRun that on, I think you'll find it'll switch in a bit. If Fluent is hitting the convergence criterion turn off Checking in the Monitor-Residual panel. nNovember 18, 2020 at 6:02 pmDrAmineAnsys EmployeeThe velocity image is telling me that is still developing. Again in 3D you should quantify it from other planes as the might be in plane but deviated.nViewing 13 reply threads
Ansys Innovation Space
- 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.Trending discussions
- Floating point exception in Fluent
- What are the differences between CFX and Fluent?
- Difference between K-epsilon and K-omega Turbulence Model
- Getting graph and tabular data from result in workbench mechanical
- The solver failed with a non-zero exit code of : 2
- Time Step Size and Courant Number
- Mesh Interfaces in ANSYS FLUENT
- Suppress Fluent to open with GUI while performing in journal file
- error: Received signal SIGSEGV
- Using GPU in FLUENT
© 2023 Copyright ANSYS, Inc. All rights reserved.Ansys does not support the usage of unauthorized Ansys software. Please visit www.ansys.com to obtain an official distribution.