Species Composition: The composition of a species source can be specified by defining a gas phase mixture. If the source involves only one species, create a single-component mixture and set the species mass fraction to 1. Only gas phase species contained in the chemistry mechanism can be used in species source. The production rate of a source mixture at a given time will be distributed among its components based on the mass fractions.

Production Rate: Four options are provided to specify the production rate of the species source mixture:

If the Per Unit Volume option is selected, the same rate will be used to modify the mass density of all fluid cells involved in the species source. If Entire Source Domain is selected, the production rate will first be converted to a Per-Unit-Volume value based on the total volume of fluid cells involved in the species source, and then the same Per-Unit-Volume rate is applied to all cells.

When the Time Varying option is selected, you should supply a Rate Profile and its Time Frame. For reciprocating engine cases, the first column of the Rate Profile must use crank angle, and the range is expected to be [0°, 360°] for a two-stroke engine and [0°, 720°] for a four-stroke engine. For non-engine cases, the first column of the profile should use time. See Profile Editor for the description of how to define the cyclic feature of the profile. For the second column of the profile, select MassFlowRate for the Per Unit Volume option, and select MassROP for the Entire Source Domain option. The Time Frame is used to define the time/crank angle delay relative to the global time/crank angle, which is useful in multi-cylinder engine simulation. For example, by defining an appropriate time-frame value for each cylinder based on the firing order, the same Rate Profile can be used for all cylinders.

Temperature Option: This input is used to specify the temperature associated with the source mixture coming into or going out of the computational domain. The source temperature is used to calculate the enthalpy of the species source. Three options are available:

If option Same As Cell Temperature is selected, the local temperature of the source mixture is assumed to be the same as the temperature in the cell interacting with the species source. For the other two options, the source temperature is prescribed and independent of the local cell temperature. For the User Specified, Time Varying option, see Profile Editor for the description of how to define the cyclic feature of the time-varying profile.

Source Location: This input is used to populate all the fluid cells involved in a species source at any given time. The following options are available:

Bounding Sphere uses a Source Center and a Source Radius to define a spherical volume. Fluid cells whose cell centers reside inside this volume are included in the source domain.

Bounding Box uses a Local Coordinate System to define the center and orientation of the box. The origin of the Local Coordinate System serves as the center of the box. The side lengths of the box are specified by Side Length X, Y, Z. In the Local Coordinate System, the lower-left and upper-right corners of the box correspond to (-X/2, -Y/2, -Z/2) and (X/2, Y/2, Z/2), respectively.

Bounding Cylinder also uses a Local Coordinate System to define its center and orientation. The origin of the Local Coordinate System serves as the center of the cylinder. The Z-axis of the Local Coordinate System will be aligned with the axis of the cylinder. Source Height and Source Radius define the height and radius of the cylinder, respectively.

Bounding Cone defines a cone or truncated cone shape. It uses two points to define the ends of the cone axis. On each end, a radius is used to define the size of the circular end surface. The end surfaces are perpendicular to the cone axis.

Bounding Annulus uses two points to define the two ends of the annulus axis. On each end of the annulus axis, an inner radius and an outer radius are used to define a ring-shaped end surface. The end surfaces are perpendicular to the annulus axis.

Initialization Region allows you to associate the source to a region. At a given time, all fluid cells in the selected region are included in the source domain.

General Data Sampling can be used to identify fluid cells associated with the source indirectly through a point cloud. In the point cloud, you can specify a group of points in terms of their X, Y, Z coordinates. Fluid cells containing any of these points will be included in the source domain.

Active: This input is used to specify when the species source will be activated and deactivated. Four options are provided:

The During Crank Angle Interval option can only be used in reciprocating engine cases. You can select the Crank Angle Option as Cyclic or Global. The Cyclic option is helpful in specifying source activation that is repetitive in a multi-engine-cycle simulation. In this case, both the Start angle and End angle will be converted to a value within the range of [0°, 360°) or [0°, 720°) for two-stroke or four-stroke engines, respectively. The CA-interval-based activation control will be treated as cyclic in engine simulations. The source activation time will then be treated as cyclic and repeated on a 720-degree schedule (4-stroke) or 360-degree schedule (2-stroke). User may choose to Use Global Crank Angle Limits to impose a global crank angle range for the cyclic repetition, beyond which the source is not active. If the Crank Angle Option is Global, no cyclic conversion is made on the user-supplied start and end crank angle value.

Momentum Direction: Specify the direction vector for the momentum source. The direction can be a uniform vector or an axisymmetric vector pattern, both can be specified as a constant or a time-varying profile. See Profile Editor for a detailed description of how to specify the axisymmetric vector pattern. The user-supplied X,Y, Z components of the uniform vector or the Radial, Tangential, Axial components of the axisymmetric vector will be normalized as a unit vector during run time, but it is recommended that you provide these input vectors as unit vectors. If a vector profile is used, the velocity direction vectors will not be interpolated between tabulated points, instead, the profile will be treated as a staircase function.

Production Rate: The options are similar as those for Species Source. Refer to the Species Source section for the list of options and general information. For a momentum source, the production rate will be applied to momentum cells instead of regular fluid cells. Note that in Forte’s staggered discretization scheme, a momentum cell’s center is a vertex and a momentum cell consists of fractions of all fluid cells surrounding this vertex.

When Entire-Source-Domain is selected, the rate value will first be converted to a Per-Unit-Volume value based on the total volume of momentum cells involved in the momentum source, and then the same Per-Unit-Volume rate is applied to all momentum cells.

When the Time-Varying option is selected, you should supply a Rate Profile. The first column of the Rate Profile (time or crank angle) should follow the same requirement described in Species Source. For the second column of the Rate Profile, select VolumetricMomentum for the Per-Unit-Volume option, and select Force for the Entire Source Domain option.

Source Location: This source location options for momentum source are the same as those for Species Source. Note that instead of collecting regular fluid cells, momentum source collects momentum cells, which center at vertices.

For the General Data Sampling option, the point cloud is first used to mark all fluid cells containing any sample point, and then all the eight vertices of the marked cells will be included in the momentum source domain.

Active: The activation control for momentum source is the same as that for Species Source.

: viscous resistance coefficient (inverse absolute permeability);

: inertial resistance coefficient.

Media Type: The porous media can be modeled as either Isotropic or Directional. For the Isotropic type, only one set of resistance coefficients is needed. For the Directional type, you can specify one streamwise direction and two transverse directions and assign different resistance coefficients for each direction. Since these three direction vectors are required to be mutually orthogonal, a convenient way to specify these vectors is to create a coordinate system. The Z axis of this coordinate system should be oriented to align with the streamwise direction of the porous medium. The X and Y axes of the coordinate system will be treated as transverse-1 and transverse-2 directions, respectively.

Source Location: The source domain/location specification for porous media is similar to those for Species Source and Momentum Source.

Active: The activation control for porous media source is the same as that for Species Source.

Production Rate: The production rate options for energy source are similar to those for Species Source. Refer to the Species Source section for general information.

When the Time Varying option is selected, the first column of the Rate Profile (time or crank angle) should follow the same requirement described in Species Source. For the second column of the Rate Profile, select HeatProductionRate for the Per-Unit-Volume option, and select Power for the Entire Source Domain option.

Energy Source also allows its production rate to be derived from a pressure curve. This is the last option on the drop-down list. When this option is used, the Source Location of the energy source must use the Initialization Region option and the region selected must be a cylinder or primary region. The energy release rate is calculated as

in which, may also be in engine cases. is the total volume of the selected cylinder/primary region, and is the averaged specific heat ratio in the region.

Source Location: The source location options for Energy Source are the same as those for Species Source.

Active: The activation control for Energy Source is the same as that for other sources, such as Species Source.