CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS > FLUENT

Reflection Free Boundary Condition

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

LinkBack Thread Tools Search this Thread Display Modes
Old   April 14, 2021, 04:02
Question Reflection Free Boundary Condition
New Member
Join Date: Apr 2021
Posts: 4
Rep Power: 2
Sanda is on a distinguished road
I am conducting pressure based transient incompressible fluid flow in viscoelastic tube in ANSYS fluent and I would like to create an absorbing boundary condition in the outlet of the tube.
ANSYS Fluent already include non-reflecting outlet boundary conditions (NRBC) but only applies for ideal gas (compressible) flow.
With Pressure Far Field BC, it is available only when density is calculated using ideal gas law.
With Outflow BC, it cannot be used for unsteady flow with variable density.
So, the last option is using UDF in the outlet of the tube and I have difficulty applying it.

I found a thesis that similar to my research approach. (
And I would like to create such boundary condition in ANSYS fluent.
In page 27 of the thesis, under Section 3.2 Boundary Conditions, in Subsection 3.2.1, the author applied reflection free boundary condition at the outlet of the vessel. I have short knowledge of how to apply the boundary condition at the outlet of a vessel.

I am learning UDF in ANSYS Fluent, but I am not sure how to apply boundary equation (Eq 106, page 28) at the outlet. I assume it will require to use UDM but the equation require to use the volume flow rate value from previous space step.
I manage to calculate in numerical analysis but Is there a tutorial to put an equation in UDF of ANSYS fluent?

Equation 106 requires to use data from the previous space exported from ANSYS so How to input a variable that need to read from the analysis?
Using UDM is one of the idea but not sure how to load the data.
Attached Images
File Type: jpg Reflection free Boundary Condition-page-001.jpg (99.4 KB, 5 views)
File Type: png Tube with fluid flow.png (55.4 KB, 3 views)
Sanda is offline   Reply With Quote

Old   October 19, 2021, 13:36
Senior Member
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 4,575
Rep Power: 53
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
I don't get it. You are incompressible. You don't have waves and you don't have wave reflections. Why are you looking into BC's for removing unwanted waves?
LuckyTran is offline   Reply With Quote


boundary condition, fluent - udf, fluid structure interface, udf and programming

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
Boundary condition setting for free surface in water tank haiteng FLUENT 1 April 6, 2020 08:55
Shear stress boundary condition at free surface yummigummi OpenFOAM Programming & Development 0 September 2, 2019 07:34
Problem in setting Boundary Condition Madhatter92 CFX 12 January 12, 2016 05:39
Question about heat transfer coefficient setting for CFX Anna Tian CFX 1 June 16, 2013 07:28
Low Mixing time Problem Mavier CFX 5 April 29, 2013 01:00

All times are GMT -4. The time now is 21:48.