# Error with the calculation of boundary cell face area magnitude in axisymmetric solve

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

January 22, 2021, 06:50
Error with the calculation of boundary cell face area magnitude in axisymmetric solve
#1
New Member

Join Date: Jan 2021
Posts: 14
Rep Power: 5
Dear colleagues and seniors, Good Day. It is my first post about a very simple error, which i recently encountered during my udf modelling.

I am currently solving a 2D axisymmetric model with hemispherical (quater Circle) boundary at which i want to calculate the magnitude of face area by using the following Macros:

F_AREA(A,f,t);
Area=NV_MAG(A);

However, the area magnitude does not agree to the grid, which i have manually designed using fixed divisions at boundary. However, when i changed my solver setting from axisymmetric space to 2D Planer, the problem is solved and i can get the required area magnitude corresponding to my grid design. So problem is with the axisymmetric consideration.

I further dig out the UDF manual and found the following solution:
"For axisymmetric models in ANSYS FLUENT are made on a 1 radian
basis. Therefore, when you are utilizing certain data access macros (e.g., F AREA or F FLUX) for axisymmetric flows, your UDF will need to multiply the result by 2*PI (utilizing the macro M PI) to get the desired value."

You can also find in the picture from CFD post, for axisymmetric solver, there is a non uniform thickness slice considered.
I modify it as:
Area = NV_MAG(A)*2.0*M_PI;

However, following this does not make any change to my results and only solution seems to solve the problem in Planer space, which i do not want.

Please give me some handy solution to solve this problem, while using axisymmetric solver setting. I am indebted to you for reviewing my error.

Danny
Attached Images
 axisymetric.JPG (36.5 KB, 11 views)

Last edited by Danny_cfd; January 22, 2021 at 07:29. Reason: Adding pic

 April 15, 2021, 07:37 #2 Member   Join Date: Nov 2017 Posts: 54 Rep Power: 8 hello Danny I Have a same problem. I couldn't calculate the area of a boundary in my axisymmetric model. when i changed the model to planar, fluent accurately calculate the area. can I ask you to help me for this problem?

April 15, 2021, 10:01
#3
Senior Member

Join Date: Nov 2013
Posts: 1,965
Rep Power: 26
Quote:
 this does not make any change to my results
I don't follow this part... How does multiplying by 2Pi not change your result?
__________________
"The UDF library you are trying to load (libudf) is not compiled for parallel use on the current platform" is NOT the error after compiling. It is the error after loading. To see compiler errors, look at your screen after you click "build".

May 11, 2021, 03:10
#4
Member

xingangzheng
Join Date: Jul 2009
Posts: 39
Rep Power: 17
Your modification for the axisymmetric problems are right. It's likely that you are using this area to calculate the mass flow through certain face. The problem may be in programming it.

Quote:
 Originally Posted by Danny_cfd Dear colleagues and seniors, Good Day. It is my first post about a very simple error, which i recently encountered during my udf modelling. I am currently solving a 2D axisymmetric model with hemispherical (quater Circle) boundary at which i want to calculate the magnitude of face area by using the following Macros: F_AREA(A,f,t); Area=NV_MAG(A); However, the area magnitude does not agree to the grid, which i have manually designed using fixed divisions at boundary. However, when i changed my solver setting from axisymmetric space to 2D Planer, the problem is solved and i can get the required area magnitude corresponding to my grid design. So problem is with the axisymmetric consideration. I further dig out the UDF manual and found the following solution: "For axisymmetric models in ANSYS FLUENT are made on a 1 radian basis. Therefore, when you are utilizing certain data access macros (e.g., F AREA or F FLUX) for axisymmetric flows, your UDF will need to multiply the result by 2*PI (utilizing the macro M PI) to get the desired value." You can also find in the picture from CFD post, for axisymmetric solver, there is a non uniform thickness slice considered. I modify it as: Area = NV_MAG(A)*2.0*M_PI; However, following this does not make any change to my results and only solution seems to solve the problem in Planer space, which i do not want. Please give me some handy solution to solve this problem, while using axisymmetric solver setting. I am indebted to you for reviewing my error. Danny

 Tags face area magnitude