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This section contains macros that you can use when defining scalar transport UDFs in ANSYS FLUENT. Note that if you try to use the macros listed below (e.g., F_UDSI, C_UDSI) before you have specified user-defined scalars in your ANSYS FLUENT model (in the User-Defined Scalars dialog box), then an error will result.
Set_User_Scalar_Name
ANSYS FLUENT assigns a default name for every user-defined scalar that you allocate in the graphical user-interface. For example, if you specify 2 as the Number of User-Defined Scalars, then two variables with default names User Scalar 0 and User Scalar 1 will be defined and the variables with these default names will appear in setup and postprocessing dialog boxes. You can change the default names if you wish, using Set_User_Scalar_Name as described below.
The default name that appears in the graphical user interface and on plots in ANSYS FLUENT for user-defined scalars (e.g., User Scalar 0) can now be changed using the function Set_User_Scalar_Name.
void Set_User_Scalar_Name(int i,char *name); |
i is the index of the scalar and name is a string containing the name you wish to assign. It is defined in sg_udms.h.
Set_User_Scalar_Name should be used only once and is best used in an EXECUTE_ON_LOADING UDF (see Section 2.2.6). Due to the mechanism used, UDS variables cannot be renamed after they have been set, so if the name is changed in a UDF, for example, and the UDF library is reloaded, then the old name could remain. In this case, restart ANSYS FLUENT and load the library again.
F_UDSI
You can use F_UDSI when you want to access face variables that are computed for user-defined scalar transport equations (Table 3.2.35). See Section 3.2.9 for an example of F_UDSI usage.
| Macro | Argument Types | Returns |
| F_UDSI(f,t,i) |
face_t f,
Thread *t,
int i
Note: i is index of scalar |
UDS face variables |
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Note that
F_UDSI is available for wall and flow boundary faces, only. If a UDS attempts to access any other face zone, then an error will result.
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C_UDSI
You can use C_UDSI when you want to access cell variables that are computed for user-defined scalar transport equations. Macros for accessing UDS cell variables are listed in Table 3.2.36. Some examples of usage for these macros include defining non-constant source terms for UDS transport equations and initializing equations. See Section 3.2.9 for an example of C_UDSI usage.
| Macro | Argument Types | Returns |
| C_UDSI(c,t,i) | cell_t c, Thread *t, int i | UDS cell variables |
| C_UDSI_G(c,t,i) | cell_t c, Thread *t, int i | UDS gradient |
| C_UDSI_M1(c,t,i) | cell_t c, Thread *t, int i | UDS previous time step |
| C_UDSI_M2(c,t,i) | cell_t c, Thread *t, int i | UDS second previous time step |
| C_UDSI_DIFF(c,t,i) |
cell_t c,
Thread *t,
int i
Note: i is index of scalar |
UDS diffusivity |
Reserving UDS Variables
Reserve_User_Scalar_Vars
The new capability of loading more than one UDF library into ANSYS FLUENT raises the possibility of user-defined scalar (UDS) clashes. To avoid data contention between multiple UDF libraries using the same user-defined scalars, ANSYS FLUENT has provided the macro Reserve_User_Scalar_Vars that allows you to reserve scalars prior to use.
int Reserve_User_Scalar_Vars(int num) |
int num is the number of user-defined scalars that the library uses. The integer returned is the lowest UDS index that the library may use. After calling:
offset = Reserve_User_Scalar_Vars(int num); |
the library may safely use C_UDSI(c,t,offset) to C_UDSI(c,t,offset+num-1). See Section 2.2.6 for an example of macro usage. Note that there are other methods you can use within UDFs to hardcode the offset to prevent data contention.
Reserve_User_Scalar_Vars (defined in sg_udms.h) is designed to be called from an EXECUTE_ON_LOADING UDF (Section 2.2.6). An on-loading UDF, as its name implies, executes as soon as the shared library is loaded into ANSYS FLUENT. The macro can also be called from an INIT or ON_DEMAND UDF. After a user scalar has bee reserved, it can be set to unique names for the particular library using Set_User_Memory_Name (see below for details on Set_User_Memory_Name). After the number of UDS that are needed by a particular library is set in the GUI and the variables are successfully reserved for the loaded library, the other functions in the library can safely use C_UDMI(c,t,offset) up to C_UDMI(c,t,offset+num-1) to store values in user scalars without interference.
Unreserving UDS Variables
ANSYS FLUENT does not currently provide the capability to unreserve UDS variables using a macro. Unreserve macros will be available in future versions of ANSYS FLUENT.
N_UDS
You can use N_UDS to access the number of user-defined scalar (UDS) transport equations that have been specified in ANSYS FLUENT. The macro takes no arguments and returns the integer number of equations. It is defined in models.h.
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3.2.7 Model-Specific Macros
