Fluent UDF Training-2

2011

ANSYS FLUENT GUIDE Advanced FLUENT User-Defined Functions You can access and manipulate almost every solver data and fully control the solution process in UDF-s written in C programming Language.

Saeed Sadeghi (www.fluent.blogfa.com) Pardad Petro Danesh (www.petrodanesh.com) Pardad Petro Danesh (www.petrodanesh.com) | Confidential 1/12/2011

Introduction

2

Table of Contents 1

Introduction ........................................... ............................................................................................ ......................................................................................... ........................................ 4

2

User Access to the FLUENT Solver.......................................... ........................................................................................... ......................................................... ........ 4

3

C Programming ............................................... ................................................................................................ ................................................................................. ................................ 5

4

Cfd Programming in FLUENT ............................................... ............................................................................................... ............................................................ ............ 7

5

UDF Basics ........................................... ............................................................................................ ............................................................................................ ........................................... 7

6

Using UDFs in the Solvers ......................................... .......................................................................................... ....................................................................... ...................... 8

7

Data structure overview.......................................... .......................................................................................... ........................................................................ ........................ 8 7.1

The Domain .......................................... .......................................................................................... ................................................................................... ................................... 8

7.2

The Threads .......................................... .......................................................................................... ................................................................................... ................................... 9

7.3

Cell and Face Datatypes ............................................ ............................................................................................ .............................................................. .............. 9

7.4

Some Additional info on Faces ............................................. ............................................................................................. ................................................... ... 9

8

Fluent UDF Data Structure Summary ........................................... ........................................................................................... .................................................. 10

9

Geometry Macros ................................................ ................................................................................................. ......................................................................... ........................ 11

10

Cell Field Variable Macros ............................................ ............................................................................................. ............................................................. ............ 12

11

Face Field Variable Macros .......................................... ........................................................................................... ............................................................. ............ 13

12

Looping and Thread Macros......................................... .......................................................................................... ............................................................. ............ 14

13

Macros .......................................... .......................................................................................... ............................................................................................. ............................................. 15

13.1

DEFINE Macros .............................................. .............................................................................................. ........................................................................ ........................ 15

13.2

Othe UDF Applications ............................................ ............................................................................................. .............................................................. ............. 16

14

User Defined Memories ............................................. .............................................................................................. ............................................................... .............. 17

15

User Defined Scalars.................................................. Scalars.................................................................................................. ................................................................ ................ 18

16

Interpreted vs. Compiled UDF’s ............................................ ............................................................................................. .................................................... ... 19

17

UDF Technical Support .............................................. ............................................................................................... ................................................................ ............... 19

18

Example: Parabolic Inlet Velocity Profile .......................................... .................................................................................. ........................................ 20

18.1

Step 1: Prepare the Source Code ............................................... .......................................................................................... ........................................... 20

18.2

Step 3: Interpret or Compile the UDF .......................................... ................................................................................... ......................................... 20

18.3

Step 4: Activate the UDF ................................................. ................................................................................................. ...................................................... ...... 21

18.4

Steps 5 and 6: Run the Calculations ........................................... ...................................................................................... ........................................... 21

18.5

Numerical Solution of the Example............................................ ....................................................................................... ........................................... 21

19

Example: Checking Effect of Porous Zone on Momentum Equation ........................................ 22

19.1

Using Fluent Built-in Porous Zone ............................................. ......................................................................................... ............................................ 22

19.2

Using Momentum Source Terms.............................. Terms............................................................................... ............................................................. ............ 23

20

Example: Modeling Fuel Cell ............................................. .............................................................................................. ........................................................ ....... 24 Saeed Sadeghi (www.fluent.blogfa.com) Pardad Petro Danesh (www.petrodanesh.com)

Introduction

3

20.1

Preparation................................................ ................................................................................................ ............................................................................ ............................ 24

20.2

Mesh............................................... ............................................................................................... ....................................................................................... ....................................... 24

20.3

General Settings .......................................... .......................................................................................... .......................................................................... .......................... 24

20.4

Models ............................................. .............................................................................................. ...................................................................................... ..................................... 25

20.5

Materials .......................................... .......................................................................................... ..................................................................................... ..................................... 25

20.6

Boundary Conditions ............................................ ............................................................................................. ................................................................. ................ 26

20.6.1

Setting Velocity Inlet .............................................. .............................................................................................. ....................................................... ....... 29

20.6.2

Pressure Outlet............................................ ............................................................................................ .................................................................. .................. 29

20.7

Writing UDF ............................................. .............................................................................................. .............................................................................. ............................. 30

20.7.1 20.8 21

Compiling the UDF................................................ UDF................................................................................................ ......................................................... ......... 32

Checking Oxygen Mass Balance .............................................. ............................................................................................ .............................................. 37 Fluent Frequently Asked Questions ............................................. .......................................................................................... ............................................. 39

21.1

My UDF won't interpret or compile - what is wrong? ............................................ .......................................................... .............. 39

21.2

How to Set Environment Variables .......................................... ....................................................................................... ............................................. 39

21.2.1

On Windows 32 Bit ............................................... ............................................................................................... ......................................................... ......... 39

21.2.2

On Windows 64 Bit ............................................... ............................................................................................... ......................................................... ......... 39

Saeed Sadeghi (www.fluent.blogfa.com) Pardad Petro Danesh (www.petrodanesh.com)

Introduction

1 •

4

Introduction What is a User Defined Function? o

A UDF is a routine (programmed by the user) written in C which can be dynamically linked with the solver. 

Standard C functions •



Pre-Defined Macros •

•

e.g., trigonometric, exponential, control blocks, do-loops, file i/o, etc. Allows access to field variable, material property, and cell geometry data.

Why build UDF’s? o

Standard interface cannot be programmed to anticipate all needs. 

Customization of boundary conditions, source terms, reaction rates, material properties, etc.

2



Adjust functions (once per iteration)



Execute on Demand functions



Solution Initialization

User Access to the FLUENT Solver

Saeed Sadeghi (www.fluent.blogfa.com) Pardad Petro Danesh (www.petrodanesh.com)

C Programming

3

5

C Programming •

Basic syntax rules: o

Each statement must be terminated with a semicolon ;

o

Comments can be inserted anywhere between /* and */

o

Variables must be explicitly declared (unlike in FORTRAN)

o

Compound statements must be enclosed by {

o

Functions have the following format:

}

return-value-type function-name (parameter-list) { function body } o •

Macros are defined in the header files, they can be used just like functions

Built-in data types: int, float, double, enum, Boolean: int niter, a;

/* declaring ‘niter’ and ‘a’ as integers */

float dx[10];

/* ‘dx’ is a real array with 10 members, the array index always starts from dx[0] */

enum { X, Y, Z }; /* X, Y, Z are enumeration constants 0, 1, 2 */ •

pointer is a special kind of variable that contains the memory address, not content, of  another variable

•

Pointers are declared using the * notation:

int *ip; •

/* ip is declared as a pointer to integer */

We can make a pointer point to the address of predefined variable as follows: int a=1; int *ip; ip = &a; /* &a returns the address of variable a */ printf(“content of address pointed to by ip = %d\n”, *ip);

•

Pointers are also used to point to the beginning of an array o

•

Thus pointers are used to address arrays in C

Array variables can be defined using the notation name[size], where name is the variable name and size is an integer which defines the number of elements in the array (from 0 to size-1)

•

Operators =

(assignment)

+, -, *, /, % (modulus) , >=,