
You can define volumetric sources of mass (for single or multiple species), momentum, energy, turbulence, and other scalar quantities in a fluid zone, or a source of energy for a solid zone. This feature is useful when you want to input a known value for these sources. (For more complicated sources with functional dependency, you can create a userdefined function as described in the separate UDF Manual.) To add source terms to a cell or group of cells, you must place the cell(s) in a separate zone. The sources are then applied to that cell zone. Typical uses for this feature are listed below:

Note that if you define a mass source for a cell zone, you should also define a momentum source and, if appropriate for your model, energy and turbulence sources. If you define only a mass source, that mass enters the domain with no momentum or thermal heat. The mass will therefore have to be accelerated and heated by the flow and, consequently, there may be a drop in velocity or temperature. This drop may or may not be perceptible, depending on the size of the source. (Note that defining only a momentum, energy, or turbulence source is acceptable.)

Sign Conventions and Units
All positive source terms indicate sources, and all negative source terms indicate sinks. All sources must be specified in SI units.
Procedure for Defining Sources
To define one or more source terms for a zone, follow these steps (remembering to use only SI units):
Mass Sources
If you have only one species in your problem, you can simply define a Mass source for that species. The units for the mass source are kg/m s. In the continuity equation ( this equation in the separate Theory Guide), the defined mass source will appear in the term.
If you have more than one species, you can specify mass sources for each individual species. There will be a total Mass source term as well as a source term listed explicitly for each species (e.g., h2, o2) except the last one you defined. If the total of all species mass sources (including the last one) is 0, then you should specify a value of 0 for the Mass source, and also specify the values of the nonzero individual species mass sources. Since you cannot specify the mass source for the last species explicitly, ANSYS FLUENT will compute it by subtracting the sum of all other species mass sources from the specified total Mass source.
For example, if the mass source for hydrogen in a hydrogenair mixture is 0.01, the mass source for oxygen is 0.02, and the mass source for nitrogen (the last species) is 0.015, you will specify a value of 0.01 in the h2 field, a value of 0.02 in the o2 field, and a value of 0.045 in the Mass field. This concept also applies within each cell if you use userdefined functions for species mass sources.
The units for the species mass sources are kg/m s. In the conservation equation for a chemical species ( this equation in the separate Theory Guide), the defined mass source will appear in the term.
Momentum Sources
To define a source of momentum, specify the X Momentum, Y Momentum, and/or Z Momentum term. The units for the momentum source are N/m . In the momentum equation ( this equation in the separate Theory Guide), the defined momentum source will appear in the term.
Energy Sources
To define a source of energy, specify an Energy term. The units for the energy source are W/m . In the energy equation ( this equation in the separate Theory Guide), the defined energy source will appear in the term.
Turbulence Sources
Turbulence Sources for the  Model
To define a source of or in the  equations, specify the Turbulent Kinetic Energy or Turbulent Dissipation Rate term. The units for the source are kg/ms and those for are kg/ms .
The defined source will appear in the term on the righthand side of the turbulent kinetic energy equation (e.g., this equation in the separate Theory Guide).
The defined source will appear in the term on the righthand side of the turbulent dissipation rate equation (e.g., this equation in the separate Theory Guide).
Turbulence Sources for the SpalartAllmaras Model
To define a source of modified turbulent viscosity, specify the Modified Turbulent Viscosity term. The units for the modified turbulent viscosity source are kg/ms . In the transport equation for the SpalartAllmaras model ( this equation in the separate Theory Guide), the defined modified turbulent viscosity source will appear in the term.
Turbulence Sources for the  Model
To define a source of or in the  equations, specify the Turbulent Kinetic Energy or Specific Dissipation Rate term. The units for the source are kg/ms and those for are kg/m s .
The defined source will appear in the term on the righthand side of the turbulent kinetic energy equation ( this equation in the separate Theory Guide).
The defined source will appear in the term on the righthand side of the specific turbulent dissipation rate equation ( this equation in the separate Theory Guide).
Turbulence Sources for the Reynolds Stress Model
To define a source of , , or the Reynolds stresses in the RSM transport equations, specify the Turbulence Kinetic Energy, Turbulence Dissipation Rate, UU Reynolds Stress, VV Reynolds Stress, WW Reynolds Stress, UV Reynolds Stress, VW Reynolds Stress, and/or UW Reynolds Stress terms. The units for the source and the sources of Reynolds stress are kg/ms , and those for are kg/ms .
The defined Reynolds stress sources will appear in the term on the righthand side of the Reynolds stress transport equation ( this equation in the separate Theory Guide).
The defined source will appear in the term on the righthand side of this equation in the separate Theory Guide.
The defined will appear in the term on the righthand side of this equation in the separate Theory Guide.
Mean Mixture Fraction and Variance Sources
To define a source of the mean mixture fraction or its variance for the nonpremixed combustion model, specify the Mean Mixture Fraction or Mixture Fraction Variance term. The units for the mean mixture fraction source are kg/m s, and those for the mixture fraction variance source are kg/m s.
The defined mean mixture fraction source will appear in the term in the transport equation for the mixture fraction ( this equation in the separate Theory Guide).
The defined mixture fraction variance source will appear in the term in the transport equation for the mixture fraction variance ( this equation in the separate Theory Guide).
If you are using the twomixturefraction approach, you can also specify sources of the Secondary Mean Mixture Fraction and Secondary Mixture Fraction Variance.
P1 Radiation Sources
To define a source for the P1 radiation model, specify the P1 term. The units for the radiation source are W/m , and the defined source will appear in the term in this equation in the separate Theory Guide.
Note that, if the source term you are defining represents a transfer from internal energy to radiative energy (e.g., absorption or emission), you will need to specify an Energy source of the same magnitude as the P1 source, but with the opposite sign, in order to ensure overall energy conservation.
Progress Variable Sources
To define a source of the progress variable for the premixed combustion model, specify the Progress Variable term. The units for the progress variable source are kg/m s, and the defined source will appear in the term in this equation in the separate Theory Guide.
NO, HCN, and NH Sources for the NOx Model
To define a source of NO, HCN, or NH for the NOx model, specify the no, hcn, or nh3 term. The units for these sources are kg/m s, and the defined sources will appear in the , , and terms of this equation in the separate Theory Guide , this equation in the separate Theory Guide , and this equation in the separate Theory Guide.
UserDefined Scalar (UDS) Sources
You can specify source term(s) for each UDS transport equation you have defined in your model. See Section 9.1.3 for details.