February 10, 2021 at 11:03 amakbanSubscriber
I want to simulate open channel flows where flow velocity and waves on interface co-exist.
My 2D geometry is shown here:February 10, 2021 at 1:17 pmRobAnsys EmployeeThe surface Free surface needs to be away from the water free surface and set as a pressure boundary but not part of the open channel. Open channel is for where the waves enter and leave the domain.nFebruary 10, 2021 at 1:36 pmakbanSubscriberDear sir,nI did what you suggest. The free surface in my image is at z=0.5 m and water free surface is at z=0.2 m. Please check pressure outlet boundary condition.nFebruary 10, 2021 at 1:46 pmRobAnsys EmployeeWhat is pressure outlet set as? You need more spare height and if the domain is only a few metres long you may want to consider how big the waves should be and what the model was designed for. nFebruary 10, 2021 at 2:27 pmakbanSubscriberThe pressure outlet is se as pressure outlet. The domain dimension: length, L=5 m, water depth, d=0.2 m, domain height, H=0.5 m. Velocity of water, v=0.2 m/s.nnPlease suggest.nFebruary 10, 2021 at 3:11 pmRobAnsys EmployeeI'd make the height enough that the waves aren't anywhere near the top of the domain. With a shallow depth you'll need to choose the wave conditions carefully, you also need more mesh in the domain to track the free surface. nFebruary 10, 2021 at 3:24 pmakbanSubscriberThanks.nFew points:nI provided a wave of zero amplitude to check if I get water flow velocity contour properly. I thought upon getting that, I would introduce waves of non-zero amplitude for future simulations. But the velocity contour came to be weird -- my main issue is with simulating the water flow.nIf my way of producing open channel flow (without wave) is wrong, please suggest the better way.nnRegards,nAyannFebruary 10, 2021 at 4:26 pmRobAnsys EmployeeDid you patch in the water? We do use the model without waves regularly for various applications. nFebruary 10, 2021 at 7:57 pmakbanSubscriberHi,nnI did try patching the water. Even with this my velocity came to be unreal. nFor example, I used only open channel option (leaving open channel wave BC) :nI used water density as compressible:nI did patch the domain of water. nBoundary conditions:nInlet- velocity inlet, noutlet & top of the domain- pressure outletnbottom- wallnnThe solution I got after 24 seconds is:nPlease suggest.nnFebruary 10, 2021 at 10:17 pmYasserSelimaSubscriberYou can ignore the compresability of water ... I am not sure is your inlet 0.5 m height or 0.2 m height (Whole domain height, or just water height)nSecond with the dimension you mention and the mesh on the first post, you will not get the free surface. You need fine mesh around the interface ...nFinally, if you simulated 24 seconds between your comments ... you are using a super super fast HPC or you are using very large time step. And most probably you don't do enough iterations to convergenFebruary 10, 2021 at 11:24 pmFebruary 10, 2021 at 11:59 pmYasserSelimaSubscriberI think you should have the inlet velocity inlet of a height of 0.2 m, not 0.5 m. If you keep it 0.5 m, you will have flow rate more than you want. Also. it might be source of instability of the free surface.nFebruary 11, 2021 at 12:08 amakbanSubscriberHi,nI tried to do so. In that case, the problem is what condition should I use for top 0.3 m? If I use pressure inlet for top 0.3 m, then it takes secondary phase by default. That's the problem.nFebruary 11, 2021 at 12:57 amYasserSelimaSubscriberYou are right, It should take the secondary phase. But you should check the open channel wave BC to be able to put the free surface at the inletnFebruary 11, 2021 at 1:01 amakbanSubscriberBut if it takes secondary phase in the top 0.3 m, where secondary phase (water) does not exist, won't it give wrong results? nFebruary 11, 2021 at 1:12 amYasserSelimaSubscriberNo, it will take airnFebruary 11, 2021 at 1:15 amakbanSubscriberThanks. I will try and inform again.nnRegards,nAyannFebruary 11, 2021 at 1:19 amakbanSubscriberOne point:nI am using velocity inlet in the water inlet. I have clicked open channel wave BC & Segregated velocity inputs, where I have provided velocity for the incoming water. Primary phase has no velocity. Please refer the image in the first message. Is it okay ?.February 11, 2021 at 9:43 amakbanSubscriberHi,nIf I use height of 0.2 m to be the inlet, then the problem is what condition should I use for top 0.3 m ? If I take pressure inlet, it takes secondary phase by default.nThat's the problem.nnFebruary 11, 2021 at 12:00 pmRobAnsys EmployeeIf you pick waves then the velocity boundary gives nnSo you specify inlet velocity for both phases. Note, you need sufficient resolution to do this. If you don't have waves we'd tend to use a velocity inlet for the water & pressure for air that's above it. nFebruary 16, 2021 at 2:39 pmakbanSubscriberHi,nI have followed all the suggestions.nMy domain height is 0.5 m, water height is 0.2 m. I have two inlets- one water inlet , and another is air inlet. Water flows in the channel and air remains stationary. I am using velocity inlet for the water & pressure inlet for air that's above it. I am using open channel wave BC option along with segregated velocity input (water velocity -0.15 m/s, air vel- 0 m/s).nMy resolution is high, time step is 0.001 (initially) and 0.01 later on.nBut velocity contour is not acceptable.nKindly suggest.nnRegards,nAyaFebruary 16, 2021 at 4:17 pmRobAnsys EmployeeIs it converged, and is the mesh resolution sufficient? nFebruary 16, 2021 at 4:31 pmakbanSubscriberYes, it is converged and the resolution is pretty highnFebruary 16, 2021 at 4:53 pmRobAnsys EmployeePictures pleasenFebruary 16, 2021 at 5:26 pmFebruary 17, 2021 at 4:08 pmRobAnsys EmployeeAnd convergence? nFebruary 17, 2021 at 5:01 pmakbanSubscriberSimulation did converge at every step.nI ran in transient. nViewing 26 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
- 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
- Difference between K-epsilon and K-omega Turbulence Model
- The solver failed with a non-zero exit code of : 2
- Time Step Size and Courant Number
- Mesh Interfaces in ANSYS FLUENT
- error: Received signal SIGSEGV
Top Rated Tags
© 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.