UDF to simulate one-way valves in ANSYS Fluent to prevent backflow

viliam_kacerik · August 2, 2021, 18:30

Hello,

I am trying to simulate a transient simulation of a system in which fluid flows in tubes. The tubes include one-way valves (=check valves), which prevent backflow in the real life. Yet, I've been having issues with defining the boundary condition to prevent backflow. It is pretty clear to me that I have to apply a custom boundary condition (UDF) on an interior wall where the check valve would sit. Yet, being new to UDFs and programming in C, I do not know how to write such a UDF, even after referring to the Fluent UDF manual: http://www.pmt.usp.br/academic/marto...F%20Manual.pdf

For example, if the one-way valve should prevent backflow in the negative-Y direction (meaning allow flow in the positive-Y direction), the algorithm should resemble such:

For every time step;
If velocity_y < 0;
then velocity_y = 0;

A more refined version would be:

For every time step;
If pressure just before the check valve < pressure just after the check valve;
then velocity_y = 0;

Could you please help me write a UDF which I could apply onto an interior wall to act as a one-way valve to prevent backflow?

I will appreciate your help,

Kind regards,

Viliam

Sun · August 26, 2021, 15:05

Hi,
I would say first check the outlet boundary conditions. Usually the backflow is caused by the BCs. If you are certain that the problem can only be resolved by an UDF. I'd suggest you start writing a very first version of it, and then you can post it here to get more help on improving it.

August 2, 2021, 18:30	UDF to simulate one-way valves in ANSYS Fluent to prevent backflow	#1
viliam_kacerik New Member Viliam Kacerik Join Date: Aug 2021 Posts: 1 Rep Power: 0	Hello, I am trying to simulate a transient simulation of a system in which fluid flows in tubes. The tubes include one-way valves (=check valves), which prevent backflow in the real life. Yet, I've been having issues with defining the boundary condition to prevent backflow. It is pretty clear to me that I have to apply a custom boundary condition (UDF) on an interior wall where the check valve would sit. Yet, being new to UDFs and programming in C, I do not know how to write such a UDF, even after referring to the Fluent UDF manual: http://www.pmt.usp.br/academic/marto...F%20Manual.pdf For example, if the one-way valve should prevent backflow in the negative-Y direction (meaning allow flow in the positive-Y direction), the algorithm should resemble such: For every time step; If velocity_y < 0; then velocity_y = 0; A more refined version would be: For every time step; If pressure just before the check valve < pressure just after the check valve; then velocity_y = 0; Could you please help me write a UDF which I could apply onto an interior wall to act as a one-way valve to prevent backflow? I will appreciate your help, Kind regards, Viliam

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August 26, 2021, 15:05		#2
Sun Senior Member Join Date: Nov 2010 Posts: 103 Rep Power: 16	Hi, I would say first check the outlet boundary conditions. Usually the backflow is caused by the BCs. If you are certain that the problem can only be resolved by an UDF. I'd suggest you start writing a very first version of it, and then you can post it here to get more help on improving it.