Question

Hello! In the MANUAL of user guide or theory guide of ANSYS FLUENT 20.0, where can I see how to use the New Expression instead of writing UDF code? Because I want to add 1 species into the inlet boundary with the concentration (kg/m^3) instead of mass fraction or mole fraction, and this is because I do not know how to write UDF codes as well. Therefore, I want to learn how to write the expression for my problem. Thank you in advance! I will thumb you up!

Answer 1

It is better to learn expression instead of UDF (used in older version). The new expression is introduced in the ANSYS to make the addition of expression or boundary conditions easier (UDF is a difficult one). Expression syntax: Data types Boolean Single value parameter Field parameter Number Note: Numbers must be assigned units using [] Eg: 5 [m/s] Single value parameter: It return a single value like time (t), iteration count (inte) and constants (PI,g) Field parameter: It return a value for each cell like pressure (p).

Main operators: + - / ** (for power) > < * For example: y=4x² + 2x Expression: (4* ***2)+(2* x) For species concentration: Mass fraction = molar weight of the component * (concentration / mixture density) mass fraction = Kg kmol/m? =no unit kmol kg/m Expression: molar weight of the component * (concentration / mixture density)