CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS

Vof dpm

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   June 14, 2024, 00:48
Smile Vof dpm
  #1
New Member
 
Alejandro
Join Date: Jun 2024
Posts: 4
Rep Power: 2
Labsim is on a distinguished road
New Member

Alejandro
Join Date: Jun 2024
Posts: 1
Rep Power: 0
Labsim is on a distinguished road
Hi,
I have a problem in a simulation in which I use a vof-dpm coupling. I have a bubble that rises through a phase of the vof and reaches the surface, I use a udf that expands the bubble based on the y coordinate of the particle, but at the same time the particle gets a Lot of velocity.
Labsim is offline   Reply With Quote

Old   June 28, 2024, 17:01
Default
  #2
Senior Member
 
Martin_Sz's Avatar
 
Marcin
Join Date: May 2014
Location: Poland, Swiebodzin
Posts: 313
Rep Power: 13
Martin_Sz is on a distinguished road
It sounds like you're encountering an unphysical increase in velocity for your bubble as it reaches the surface in your VOF-DPM coupled simulation. Here are some potential causes and solutions to consider:
* Unbalanced Forces: During bubble expansion, an imbalance between the buoyancy force, drag force, and the force applied by the UDF might be causing the velocity spike. Try reviewing your UDF to ensure it introduces a smooth and balanced force based on the y-coordinate.
* Mesh Resolution: A coarse mesh near the surface could be capturing the bubble expansion inaccurately, leading to numerical instability and velocity spikes. Refine the mesh around the bubble's trajectory to improve accuracy.
* UDF Implementation: Double-check your UDF implementation for any errors that might be causing the force to be applied incorrectly. Consider simplifying the UDF logic to isolate any potential issues.
* Drag Calculation: Ensure your drag force calculation considers the bubble's deformation and velocity accurately. Explore drag models suitable for spherical or ellipsoidal bubbles depending on how your UDF expands the bubble.
* Time Stepping: If the velocity increase is instantaneous, it might be related to the time step. Try reducing the time step to capture the bubble's motion more accurately.
If these suggestions don't resolve the issue, consider consulting Ansys resources or user forums for more specific guidance related to your UDF implementation and CFD software.
__________________
Quick Tips and Tricks, Tutorials FLuent/ CFX (CFD)
https://howtooansys.blogspot.com/
Martin_Sz is offline   Reply With Quote

Old   September 26, 2024, 18:55
Default
  #3
New Member
 
Alejandro
Join Date: Jun 2024
Posts: 4
Rep Power: 2
Labsim is on a distinguished road
Quote:
Originally Posted by Martin_Sz View Post
It sounds like you're encountering an unphysical increase in velocity for your bubble as it reaches the surface in your VOF-DPM coupled simulation. Here are some potential causes and solutions to consider:
* Unbalanced Forces: During bubble expansion, an imbalance between the buoyancy force, drag force, and the force applied by the UDF might be causing the velocity spike. Try reviewing your UDF to ensure it introduces a smooth and balanced force based on the y-coordinate.
* Mesh Resolution: A coarse mesh near the surface could be capturing the bubble expansion inaccurately, leading to numerical instability and velocity spikes. Refine the mesh around the bubble's trajectory to improve accuracy.
* UDF Implementation: Double-check your UDF implementation for any errors that might be causing the force to be applied incorrectly. Consider simplifying the UDF logic to isolate any potential issues.
* Drag Calculation: Ensure your drag force calculation considers the bubble's deformation and velocity accurately. Explore drag models suitable for spherical or ellipsoidal bubbles depending on how your UDF expands the bubble.
* Time Stepping: If the velocity increase is instantaneous, it might be related to the time step. Try reducing the time step to capture the bubble's motion more accurately.
If these suggestions don't resolve the issue, consider consulting Ansys resources or user forums for more specific guidance related to your UDF implementation and CFD software.
Hello, thank you for your attention. I have been working on the model but have not been able to correct the issue. Below, I am sharing another forum where the same situation was discussed; I worked in the same way, and it generated the same problem for me. The mesh resolution and UDF-related issues have already been solved and tested on several occasions. As the particle approaches the interface, it accelerates and expands (which is how it should behave), but the continuous phase of the VOF still disperses in an unrealistic manner. I am considering interfacial tension forces through the CSF model. Another topic to consider is the turbulent dispersion constant
Labsim is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
how to couple VOF and DPM ?? cfdiscool FLUENT 7 July 18, 2024 04:02
DPM to VoF in FLUENT Cooper24 FLUENT 0 June 3, 2024 03:33
What to use- VOF or DPM for liquid spray from an injector? amoli123 Fluent Multiphase 4 December 16, 2020 06:15
Volume fraction of dispersed phase to determine DPM, VOF, Mixture model Mohsin FLUENT 5 March 5, 2018 08:47
Possibility of combining DPM and VOF Kelly FLUENT 0 September 24, 2007 17:12


All times are GMT -4. The time now is 06:27.