January 30, 2018 at 7:27 amMara25Subscriber
i'm trying to simulate a two-phase flow (water(99%) +air(1%)) inside a centrifugal pump. I'm using CFX.
I set up air as a dispersed fluid(mean diamter 0.5mm) and water as the continuous one. My inlet condition is the BulkMassFlow and the values of the volume fraction (air=0.01 and water=0.99). At the outlet i set the static pressure.
When the simulation is over in post-processing it looks like that CFX "loosing" the air fraction directly after the inlet. Therefore I have only a two phase flow at the inlet and in the rest of the pump the air is vanished. (See the attatched picture)
CFX set the default value for minimum volume fraction of 1.0E-15.
But if i choose in CFX-Pre to set up a value for the minimum volume fraction the simulation diverged and i get a "fatal overflow" error...
Does somebody know how i can fix it? I would be very grateful!
January 30, 2018 at 4:01 pmRaef.KobeissiSubscriberHi
Can you please attach the case file. Someone in the forum who uses CFX will hopefully assist you.
January 31, 2018 at 7:27 amMara25Subscriber
Thank you so much for your response!
I attached the case file.
January 31, 2018 at 4:57 pm
February 1, 2018 at 8:25 amMara25Subscriber
I tried but the file is too big to upload it, even if i don't archive the result/ solution files.
February 1, 2018 at 12:35 pmpeteroznewmanSubscriber
Go into Mesh and Clear Generated Data, then save and Archive. That will reduce the file size significantly if the Mesh was included before.
February 1, 2018 at 12:56 pmMara25Subscriber
Now it worked out.
February 1, 2018 at 5:42 pmraul.raghavSubscriber
A quick look at your simulation setup, I don't see the "Initialization" tab. Did you initialize your problem before running it?
And is there a reason why you chose "Auto Timescale: 0.001". That's too small of a timestep value than required for the problem, in my opinion. Since your rotation speed is 540 rpm, your angular velocity would be approx. 57 rad/s and CFX suggests you use (1/angular velocity) as the Physical Timestep for your simulation, which would be 0.0175 s.
Can you fix these problems and let us know how it goes?
February 2, 2018 at 11:56 amMara25Subscriber
Thank you for your answer Rahul!
I did initialize the problem before running it, but it didn't work.
I set the Auto Timescale with 0.001 that small, because when i set it to 1.0 the simulation will return an error(fatal overflow in linear solver). I also read that a smaller Auto Timescale should be chosen for multiphase flow. I tried a few different Auto Timescales and get the "best" results with 0.001.
Do you know what other reasons there could be why the air is "vanished"?
February 2, 2018 at 2:21 pmraul.raghavSubscriber
Could you possibly zip your entire workbench folder and share it through a onedrive or gdrive link? I'd like to make some changes, run it and see if I can figure something out.
- The topic ‘two-phase-flow in a centrifugal pump’ is closed to new replies.
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.
- 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.