ANSYS FLUENT 12.0 UDF Manual - 3.2.7 Model-Specific Macros

3.2.7 Model-Specific Macros

DPM Macros

The macros listed in Tables 3.2.26- 3.2.31 can be used to return real variables associated with the Discrete Phase Model (DPM), in SI units. They are typically used in DPM UDFs that are described in Section 2.5. The variables are available in both the pressure-based and the density-based solver. The macros are defined in the dpm.h header file, which is included in udf.h.

The variable p indicates a pointer to the Tracked_Particle structure ( Tracked_Particle *p) which gives you the value for the particle at the current position.

Refer to the following sections for examples of UDFs that utilize some of these macros: Section 2.5.7, Section 2.5.1, Section 2.5.6, Section 2.5.13, and Section 2.5.9.

**Table 3.2.26:** Macros for Particles at Current Position Defined in `dpm.h`
Macro	Argument Types	Returns
`P_POS(p)[i]`	`Tracked_Particle *p` `int i`	position `i`= `0`, `1`, `2`
`P_VEL(p)[i]`	`Tracked_Particle *p` `int i`	velocity `i`= `0`, `1`, `2`
`P_DIAM(p)`	`Tracked_Particle *p`	diameter
`P_T(p)`	`Tracked_Particle *p`	temperature
`P_RHO(p)`	`Tracked_Particle *p`	density
`P_MASS(p)`	`Tracked_Particle *p`	mass
`P_TIME(p)`	`Tracked_Particle *p`	current particle time
`P_DT(p)`	`Tracked_Particle *p`	time step
`P_FLOW_RATE(p)`	`Tracked_Particle *p`	flow rate of particles in a stream in kg/s (see below for details)
`P_LF(p)`	`Tracked_Particle *p`	liquid fraction (wet combusting particles only)
`P_VFF(p)`	`Tracked_Particle *p`	volatile fraction (combusting particles only)

P_FLOW_RATE(p)

Each particle in a steady flow calculation represents a "stream'' of many particles that follow the same path. The number of particles in this stream that passes a particular point in a second is the "strength'' of the stream. P_FLOW_RATE returns the strength multiplied by P_MASS(p) at the current particle position.

**Table 3.2.27:** Macros for Particles at Entry to Current Cell Defined in `dpm.h`
Macro	Argument Types	Returns
`P_POS0(p)[i]`	`Tracked_Particle *p` `int i`	position `i`= `0`, `1`, `2`
`P_VEL0(p)[i]`	`Tracked_Particle *p` `int i`	velocity `i`= `0`, `1`, `2`
`P_DIAM0(p)`	`Tracked_Particle *p`	diameter
`P_T0(p)`	`Tracked_Particle *p`	temperature
`P_RHO0(p)`	`Tracked_Particle *p`	density
`P_MASS0(p)`	`Tracked_Particle *p`	mass
`P_TIME0(p)`	`Tracked_Particle *p`	particle time at entry
`P_LF0(p)`	`Tracked_Particle *p`	liquid fraction (wet combusting particles only)

Note that when you are the using the macros listed in Table 3.2.27 to track transient particles, the particle state is the beginning of the fluid flow time step only if the particle does not cross a cell boundary.

**Table 3.2.28:** Macros for Particle Cell Index and Thread Pointer Defined in `dpm.h`
Name(Arguments)	Argument Types	Returns
`P_CELL(p)`	`Tracked_Particle *p`	cell index of the cell that the particle is currently in
`P_CELL_THREAD(p)`	`Tracked_Particle *p`	pointer to the thread of the cell that the particle is currently in

**Table 3.2.29:** Macros for Particles at Injection into Domain Defined in `dpm.h`
Macro	Argument Types	Returns
`P_INIT_POS(p)[i]`	`Tracked_Particle *p` `int i`	position `i`= `0`, `1`, `2`
`P_INIT_VEL(p)[i]`	`Tracked_Particle *p` `int i`	velocity `i`= `0`, `1`, `2`
`P_INIT_DIAM(p)`	`Tracked_Particle *p`	diameter
`P_INIT_TEMP(p)`	`Tracked_Particle *p`	temperature
`P_INIT_RHO(p)`	`Tracked_Particle *p`	density
`P_INIT_MASS(p)`	`Tracked_Particle *p`	mass
`P_INIT_LF(p)`	`Tracked_Particle *p`	liquid fraction (wet combusting particles only)

**Table 3.2.30:** Macros for Particle Species, Laws, and User Scalars Defined in `dpm.h`
Macro	Argument Types	Returns
`P_EVAP_SPECIES_INDEX(p)`	`Tracked_Particle *p`	evaporating species index in mixture
`P_DEVOL_SPECIES_INDEX(p)`	`Tracked_Particle *p`	devolatilizing species index in mixture.
`P_OXID_SPECIES_INDEX(p)`	`Tracked_Particle *p`	oxidizing species index in mixture
`P_PROD_SPECIES_INDEX(p)`	`Tracked_Particle *p`	combustion products species index in mixture
`P_CURRENT_LAW(p)`	`Tracked_Particle *p`	current particle law index
`P_NEXT_LAW(p)`	`Tracked_Particle *p`	next particle law index
`P_USER_REAL(p,i)`	`Tracked_Particle *p`	storage array for user-defined values (indexed by `i`)

**Table 3.2.31:** Macros for Particle Material Properties Defined in `dpm.h`
Macro	Argument Types	Returns
`P_MATERIAL(p)`	`Tracked_Particle *p`	material pointer
`DPM_BOILING_TEMPERATURE` `(p,m)`	`Tracked_Particle p`, `Material m`	boiling temperature
`DPM_CHAR_FRACTION(p)`	`Tracked_Particle *p`	char fraction
`DPM_DIFFUSION_COEFF(p,t)`	`Tracked_Particle *p`, `particle temperature t`	diffusion coefficient to be used the gaseous boundary layer around particle
`DPM_EMISSIVITY(p,m)`	`Tracked_Particle p`, `Material m`	emissivity for the radiation model
`DPM_EVAPORATION_`	`Tracked_Particle *p`, `TEMPERATURE(p,m)`	evaporation temperature
`DPM_HEAT_OF_PYROLYSIS(p)`	`Tracked_Particle *p`	heat of pyrolysis
`DPM_HEAT_OF_REACTION(p)`	`Tracked_Particle *p`	heat of reaction
`DPM_LATENT_HEAT(p)`	`Tracked_Particle *p`	latent heat
`DPM_LIQUID_SPECIFIC_HEAT` `(p,t)`	`Tracked_Particle *p`, `particle temperature t` Note: particle temp. typically determined by `P_T(p)`	specific heat of material used for liquid associated with particle
`DPM_MU(p)`	`Tracked_Particle *p`	dynamic viscosity of droplets
`DPM_SCATT_FACTOR(p,m)`	`Tracked_Particle p`, `Material m`	scattering factor for radiation model
`DPM_SPECIFIC_HEAT(p,t)`	`Tracked_Particle *p`, `particle temperature t` Note: particle tem- perature is typically determined by `P_T(p)`	specific heat at temperature `t`
`DPM_SWELLING_COEFF(p)`	`Tracked_Particle *p`	swelling coefficient for devolatilization
`DPM_SURFTEN(p)`	`Tracked_Particle *p`	surface tension of droplets
`DPM_VAPOR_PRESSURE(p,m)`	`Tracked_Particle p`, `Material m`	vapor pressure of liquid part of particle
`DPM_VAPOR_TEMP(p,m)`	`Tracked_Particle p`, `Material m`	vaporization temperature used to switch to vaporization law
`DPM_VOLATILE_FRACTION(p)`	`Tracked_Particle *p`	volatile fraction

NOx Macros

The following macros can be used in NOx model UDFs in the calculation of pollutant rates. These macros are defined in the header file sg_nox.h, which is included in udf.h. They can be used to return real NOx variables in SI units, and are available in both the pressure-based and the density-based solver. See Section 2.3.12 for examples of DEFINE_NOX_RATE UDFs that utilize these macros.

**Table 3.2.32:** Macros for NOx UDFs Defined in `sg_nox.h`
Macro	Returns
`POLLUT_EQN(Pollut_Par)`	index of pollutant equation being solved (see below)
`MOLECON(Pollut,SPE)`	molar concentration of species specified by `SPE` (see below)
`NULLIDX(Pollut_Par,SPE)`	TRUE if the species specified by `SPE` doesn't exist in ANSYS FLUENT case (i.e., in the Species dialog box)
`ARRH(Pollut,K)`	Arrhenius rate calculated from the constants specified by `K` (see below)
`POLLUT_FRATE(Pollut)`	production rate of the pollutant species being solved
`POLLUT_RRATE(Pollut)`	reduction rate of the pollutant species being solved
`POLLUT_QRATE(Pollut)`	quasi-steady rate of N O formation (if the quasi-steady model is used)
`POLLUT_FLUCTDEN(Pollut)`	fluctuating density value (or, if no PDF model is used, mean density at a given cell
`POLLUT_FLUCTTEM(Pollut)`	fluctuating temperature value (or, if no PDF model is used, mean temperature at a given cell)
`POLLUT_FLUCTYI(Pollut,SPE)`	fluctuating mass fraction value (or, if no PDF model is used, mean mass fraction at a given cell) of the species given by index `SPE`
`POLLUT_CTMAX(Pollut_Par)`	upper limit for the temperature PDF integration (see below)

Pollut_Par is a pointer to the Pollut_Parameter data structure that contains auxiliary data common to all pollutant species and NOx is a pointer to the NOx_Parameter data structure that contains data specific to the NOx model.

POLLUT_EQN(Pollut_Par) returns the index of the pollutant equation currently being solved. The indices are EQ_NO for NO, EQ_HCN for HCN, EQ_N2O for N $_{2}$ O, and EQ_NH3 for NH $_{3}$ .
MOLECON(Pollut,SPE) returns the molar concentration of a species specified by SPE, which is either the name of the species or IDX(i) when the species is a pollutant (like NO). SPE must be replaced by one of the following identifiers: FUEL, O2, O, OH, H2O, N2, N, CH, CH2, CH3, IDX(NO), IDX(N2O), IDX(HCN), IDX(NH3). For example, for O molar concentration you should call MOLECON(Pollut, O2), whereas for NO molar concentration the call should be MOLECON(Pollut, IDX(NO)). The identifier FUEL represents the fuel species as specified in the Fuel Species drop-down list under Prompt NO Parameters in the NOx Model dialog box.
ARRH(Pollut,K) returns the Arrhenius rate calculated from the constants specified by K. K is defined using the Rate_Const data type and has three elements - , , and . The Arrhenius rate is given in the form of

$R = AT^B\exp(-C/T)$

where is the temperature.
Note that the units of must be in m-gmol-J-s.
POLLUT_CTMAX(Pollut_Par) can be used to modify the $T_{\rm max}$ value used as the upper limit for the integration of the temperature PDF (when temperature is accounted for in the turbulence interaction modeling). You must make sure not to put this macro under any conditions within the UDF (e.g., IN_PDF or OUT_PDF).

SOx Macros

The following macros can be used in SOx model UDFs in the calculation of pollutant rates. These macros are defined in the header file sg_nox.h, which is included in udf.h. They can be used to return real SOx variables in SI units and are available in both the pressure-based and the density-based solver. See Section 2.3.20 for examples of DEFINE_SOX_RATE UDFs that utilize these macros.

**Table 3.2.33:** Macros for SOx UDFs Defined in `sg_nox.h`
Macro	Returns
`POLLUT_EQN(Pollut_Par)`	index of pollutant equation being solved (see below)
`MOLECON(Pollut,SPE)`	molar concentration of species specified by `SPE` (see below)
`NULLIDX(Pollut_Par,SPE)`	TRUE if the species specified by `SPE` doesn't exist in ANSYS FLUENT case (i.e., in the Species dialog box)
`ARRH(Pollut,K)`	Arrhenius rate calculated from the constants specified by `K` (see below)
`POLLUT_FRATE(Pollut)`	production rate of the pollutant species being solved
`POLLUT_RRATE(Pollut)`	reduction rate of the pollutant species being solved
`POLLUT_FLUCTDEN(Pollut)`	fluctuating density value (or, if no PDF model is used, mean density at a given cell)
`POLLUT_FLUCTTEM(Pollut)`	fluctuating temperature value (or, if no PDF model is used, mean temperature at a given cell)
`POLLUT_FLUCTYI(Pollut,SPE)`	fluctuating mass fraction value (or, if no PDF model is used, mean mass fraction at a given cell) of the species given by index `SPE`
`POLLUT_CTMAX(Pollut_Par)`	upper limit for the temperature PDF integration (see below)

Pollut_Par is a pointer to the Pollut_Parameter data structure that contains auxiliary data common to all pollutant species and SOx is a pointer to the SOx_Parameter data structure that contains data specific to the SOx model.

POLLUT_EQN(Pollut_Par) returns the index of the pollutant equation currently being solved. The indices are EQ_SO2 for SO and EQ_SO3 for SO , etc.
MOLECON(Pollut, SPE) returns the molar concentration of a species specified by SPE. SPE is either the name of the species or IDX(i) when the species is a pollutant (like SO ). For example, for O molar concentration you should call MOLECON(Pollut, O2), whereas for SO molar concentration the call should be MOLECON(Pollut, IDX(SO2)).
ARRH(Pollut,K) returns the Arrhenius rate calculated from the constants specified by K. K is defined using the Rate_Const data type and has three elements - , , and . The Arrhenius rate is given in the form of

$R = AT^B\exp(-C/T)$

where is the temperature.
Note that the units of must be in m-gmol-J-s.
POLLUT_CTMAX(Pollut_Par) can be used to modify the $T_{\rm max}$ value used as the upper limit for the integration of the temperature PDF (when temperature is accounted for in the turbulence interaction modeling). You must make sure not to put this macro under any conditions within the UDF (e.g., IN_PDF or OUT_PDF).

Dynamic Mesh Macros

The macros listed in Table 3.2.34 are useful in dynamic mesh UDFs. The argument dt is a pointer to the dynamic thread structure, and time is a real value. These macros are defined in the dynamesh_tools.h.

**Table 3.2.34:** Macros for Dynamic Mesh Variables Defined in `dynamesh_tools.h`
Name(Arguments)	Argument Types	Returns
`DT_THREAD(dt)`	`Dynamic_Thread *dt`	pointer to a thread
`DT_CG(dt)`	`Dynamic_Thread *dt`	center of gravity vector
`DT_VEL_CG(dt)`	`Dynamic_Thread *dt`	cg velocity vector
`DT_OMEGA_CG(t)`	`Dynamic_Thread *dt`	angular velocity vector
`DT_THETA(dt)`	`Dynamic_Thread *dt`	orientation of body-fixed axis vector
`DYNAMESH_CURRENT_TIME`	N/A	current dynamic mesh time
`TIME_TO_ABSOLUTE_CRANK_ANGLE`( `time`)	`real time`	absolute value of the crank angle

See Section 2.6.4 for an example UDF that utilizes DT_THREAD.

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