Engine Part Surface

A velocity inlet boundary represents an inflow boundary that allows you to set a specific velocity magnitude. The flow direction is normal to the boundary face. For more information, see Velocity Inlet.

Fuel/Oxidizer Mixing State Specification (only if the ECFM-3Z or the ECFM-CLEH engine model is selected)

Specifies whether the fuel and oxidizer at the flow boundary are Unmixed or Premixed at the subgrid level.

Turbulence Specification (for RANS simulations)

Controls how you define the turbulence profile at the flow boundary. The following options are available:

• K + Epsilon
• Intensity + Length Scale
• Intensity + Viscosita Ratio

For more information on these options and their corresponding value nodes, see K-Epsilon Boundaries Reference.

Static Temperature

Specifies the static temperature of the inflowing fluid.

The following options are available:

• Constant: Sets the temperature to the specified value. The default setting $DefaultAmbientTemperature equals the specified Default Wall Temperature, see Solvers Reference—Operating Conditions.
• Table: Specifies the temperature in the form of a table that defines the temperature as a function of crank angle.

  Simcenter STAR-CCM+ In-cylinder uses linear interpolation between the data points.

  • File: Sets the file that contains the temperature data.

    Import allows you to import a table of one of the following file formats: *.csv, *.txt, or *.dat.

  • Crank Angle Column: Sets the header of the column that contains the crank angle values.
  • Temperature Column: Sets the header of the column that contains the temperature values.
  • Crank Angle Units: Sets the units of the imported crank angle values—deg or radian.
  • Temperature Units: Sets the units of the imported temperature values— C, F, K, or R.

  If no table headers are available, Simcenter STAR-CCM+ In-cylinder numbers the columns starting from zero, such as column0.

Velocity Magnitude

Specifies the constant magnitude of the inflow velocity. The flow direction is normal to the boundary face.

Species Mass Fraction

When Automatic Composition Initialization is On, displays the calculated mass weighting of air, exhaust, and fuel vapor in the inflowing gas mixture. For more information, see In-cylinder Formulation—Gas Initialization and Boundary Conditions

When Automatic Composition Initialization is Off, allows you to specify the mass weighting.

Simcenter STAR-CCM+ In-cylinder calculates a given material property, such as density, of the gas mixture as:

$${\varphi }_{\mathrm{mix}}={Y_{air}\varphi }_{air}+{Y_{exhaust}\varphi }_{exhaust}+{Y_{fuel}\varphi }_{fuel}$$

(587)

with:

$$Y_{air}=\frac{W_{air}}{W_{air}+W_{exhaust}+W_{fuel}}$$

(588)

$$Y_{exhaust}=\frac{W_{exhaust}}{W_{air}+W_{exhaust}+W_{fuel}}$$

(589)

$$Y_{fuel}=\frac{W_{fuel}}{W_{air}+W_{exhaust}+W_{fuel}}$$

(590)

where:

• $W_{air}$, $W_{exhaust}$, and $W_{fuel}$ are the specified Air Mass Weighting, Exhaust Mass Weighting, and Fuel Mass Weighting, respectively.
• ${\varphi }_{air}$, ${\varphi }_{exhaust}$, and ${\varphi }_{fuel}$ are the material property values of air, exhaust and fuel vapor, respectively, as defined in Materials.

A pressure outlet boundary represents an outflow boundary that requires the specification of the pressure across the outlet. In Simcenter STAR-CCM+ In-cylinder, the pressure outlet boundary is also used for inlets. For more information, see Pressure Outlet.

Backflow Specification

Pressure

Specifies how the pressure is computed.

The following options are available:

• Environmental: Subtracts the dynamic head at the pressure outlet boundary.
• Static: Does not use dynamic head in the case of inflow. Pressure is maintained at the specified pressure.

Direction

Specifies the direction of the incoming flow.

The following options are available:

• Extrapolated: Extrapolates the flow direction from the interior of the domain. In most situations, this is less stable than the Boundary Normal option. However, it is recommended for situations where the flow is known to be parallel to the pressure boundary.
• Boundary Normal: Assumes that the incoming flow enters the simulation along a vector that is orthogonal to the boundary surface. This option generally provides the most robust convergence. If the flow is largely parallel to the boundary, the Extrapolated option should be used instead.
• Components: Allows you to explicitly define an inflow direction vector. You specify the vector in the Simulation object tree under Regions > Gases > Boundaries > [flow boundary] > Physics Values > Flow Direction > By Surface Subgroup > FlowDirectionProfile_subgroup 1.

Scalars

Specifies how scalars are computed.

The following options are available:

• Specified: When the flow reverses, the scalar conditions that you specify at the boundary are used. Otherwise, the scalar conditions are extrapolated.
• Extrapolated: Regardless of the flow direction, the scalar conditions at the boundary are set to be equal to the scalar conditions of the immediate interior.

Pressure Outlet Option

Controls the pressure conditions at the outlet.

The following options are available:

• None: Applies the default conditions.
• Pressure Jump: Imposes a pressure jump on the outlet. The available Pressure Jump Options are:
  • None: Does not apply a pressure jump on the boundary.
  • Fan: Imposes a pressure jump that is obtained from a fan performance curve that you specify. A fan performance curve describes the pressure rise across the fan—that is the static pressure measured downstream of the fan minus the total pressure that is measured upstream of the fan—as a function of the volumetric flow rate. The following Fan Curve Type options are available:
    • Polynomial: Defines the fan curve as a linear function. The pressure rise across the boundary is calculated as

      $p\left(\dot{v}\right)=-\frac{p_{\max }}{{\dot{v}}_{\max }}\dot{v}+p_{\max }$

      where $p_{\max }$ and ${\dot{v}}_{\max }$ are the specified Maximum Pressure and Maximum Flow, respectively.
    • Table: Defines the fan curve as a table of pressure rise versus volumetric flow rate as indicated by the imported Fan Curve File (*.csv). After the import, select the appropriate Pressure Units and Volume Flow Units. The pressure rise is calculated by linear interpolation between the data points in the table. Outside the intervals, the nearest limit is used.

    The specified fan performance curve must correspond to the actual fan operating rotation rate and temperature. If your data correspond to some standard rotation rate and temperature, scale the fan performance curve as required using the following established fan laws:

    $$\Delta P_2=\Delta P_1\times {({\omega }_2/{\omega }_1)}^2\times (T_1/T_2)$$
    $${\psi }_2={\psi }_1({\omega }_2/{\omega }_1)$$

    where $\omega$ is the fan rotation rate (rpm), T is the fluid temperature (K), and $\psi$ is the volumetric flow rate.

Fuel/Oxidizer Mixing State Specification (only if the ECFM-3Z or the ECFM-CLEH engine model is selected)

As for Velocity Inlet.

Turbulence Specification (for RANS simulations)

As for Velocity Inlet.

Absolute Total Pressure (for Inlet) / Absolute Static Pressure (for Outlet)

Specifies the absolute total pressure or absolute static pressure at the flow boundary in the form of a Table.

The table must define the pressure as a function of crank angle.

Simcenter STAR-CCM+ In-cylinder uses linear interpolation between the data points.

• File: Sets the file that contains the pressure data.

  Import allows you to import a table of one of the following file formats: *.csv, *.txt, or *.dat.

• Crank Angle Column: Sets the header of the column that contains the crank angle values.
• Absolute Total Pressure Column / Absolute Static Pressure Column: Sets the header of the column that contains the pressure values.
• Crank Angle Units: Sets the units of the imported crank angle values—deg or radian.
• Absolute Total Pressure Units / Absolute Static Pressure Units: Sets the units of the imported pressure values— Pa, bar, or psi.

If no table headers are available, Simcenter STAR-CCM+ In-cylinder numbers the columns starting from zero, such as column0.

Static Temperature (only when Scalars is set to Specified)

As for Velocity Inlet.

Species Mass Fraction (only when Scalars is set to Specified)

As for Velocity Inlet.

Mass Flow Option

Controls the specification of the mass flow.

The following options are available:

• Mass Flux: Sets the mass flow rate per unit area. For the Mass Flux value, the following options are available:
  • Constant: Sets the mass flux to the specified value.
  • Table: Defines the mass flux as a function of crank angle in the form of a table. For the table properties, see Pressure at Pressure Outlet using Mass Flux Column and Mass Flux Units (kg/m^2-s or lb/ft^2-s), respectively.
• Mass Flow Rate: Sets the total mass per unit time for the whole boundary. For the Mass Flow Rate value, the following options are available:
  • Constant: Sets the mass flow rate to the specified value.
  • Table: Defines the mass flow rate as a function of crank angle in the form of a table. For the table properties, see Pressure at Pressure Outlet using Mass Flow Rate Column and Mass Flow Rate Units (kg/s or lb/s), respectively.

Fuel/Oxidizer Mixing State Specification (only if the ECFM-3Z or the ECFM-CLEH engine model is selected)

As for Velocity Inlet.

Turbulence Specification (for RANS simulations)

As for Velocity Inlet.

Supersonic Static Pressure

Specifies the pressure for Supersonic Flow in the form of a Table. For subsonic flow, the pressure is extrapolated from the adjacent cell using reconstruction gradients.

For the table properties, see Pressure at Pressure Outlet.

Total Temperature

Specifies the total temperature of the upstream plenum. For the available options, see Static Temperature at Velocity Inlet using a default value of 300. 0 K for the Constant option.

Species Mass Fraction

As for Velocity Inlet.

A stagnation inlet boundary represents an inflow boundary that enables you to set the conditions of an imaginary plenum, far upstream, in which the flow is completely at rest. For more information, see Stagnation Inlet.

Stagnation Inlet Option

Controls the pressure conditions at the inlet.

The following options are available:

• None: Applies the default conditions.
• Pressure Jump: Imposes a pressure jump on the inlet. The available Pressure Jump Options are:
  • None: As for Pressure Outlet Option at Pressure Outlet.
  • Fan: As for Pressure Outlet Option at Pressure Outlet.
  • Loss Coefficient: Computes the pressure loss as $0.5K\rho {\left|v\right|}^2$ where $K$ is the specified Pressure Loss Coefficient value.

Fuel/Oxidizer Mixing State Specification (only if the ECFM-3Z or the ECFM-CLEH engine model is selected)

As for Velocity Inlet.

Turbulence Specification (for RANS simulations)

As for Velocity Inlet.

Total Pressure

Specifies the total pressure upstream of the simulation domain in the form of a Table.

For the table properties, see Pressure at Pressure Outlet.

Supersonic Static Pressure

As for Mass Flow Inlet.

Total Temperature

As for Mass Flow Inlet.

Species Mass Fraction

As for Velocity Inlet.

A symmetry plane boundary represents an imaginary plane of symmetry in the simulation. The solution that is obtained with a symmetry plane boundary is identical to the solution that would be obtained by mirroring the mesh about the symmetry plane (in half the resulting domain). For more information, see Symmetry Plane.

A wall boundary represents a flow impermeable boundary. For more information, see Wall.

Shear Stress Specification

Controls how the wall surface acts on the gas passing along it. The following options are available:

• No-Slip—with this method, the fluid sticks to the wall and moves with the same velocity as the wall. Thus, for a stationary wall, the fluid has zero velocity at the wall.
• Slip—with this method, the wall represents an impenetrable but traction-free surface.

Thermal Specification

Controls the thermal conditions at the wall. The following options are available:

• Temperature: Sets the boundary temperature to the specified Static Temperature value. The default setting $DefaultAmbientTemperature equals the specified Default Wall Temperature, see Solvers Reference—Operating Conditions.
• Adiabatic: Does not permit heat transfer across the boundary.

Wall Surface Specification (if Shear Stress Specification is set to No-Slip)

Controls the finish of the surface. The following options are available:

• Smooth: Regular wall treatment for an even wall.
• Rough: Modifies the wall treatment to incorporate roughness as indicated by the specified Roughness Height.

Static Temperature

Specifies the static temperature of the wall.

The following options are available:

• Constant: as for Velocity Inlet
• Table: as for Velocity Inlet.
• Table XYZ: specifies the temperature in the form of a Table(x,y,z) that defines the temperature as a function of location.

  The table must have three columns that specify the ’X’, ’Y’, and ’Z’ values of the location in the Laboratory coordinate system. A fourth column specifies the temperature value to be mapped at that location. The column headers can contain units, which are specified within a set of parentheses as part of the variable name, such as ’X (mm)’. If no units are specified, Simcenter STAR-CCM+ In-cylinder uses SI units.

  Note	The table must provide coordinates and temperature data for the engine with all valves closed and the piston at BDC.

  To map the tabular data to the mesh, Simcenter STAR-CCM+ In-cylinder uses nearest-neighbor interpolation.

  • File: Sets the file that contains the coordinates and temperature data.

    Import allows you to import a table of one of the following file formats: *.csv, *.txt, or *.dat.

  • Temperature Column: Sets the header of the column that contains the temperature values.

Roughness Height

Specifies the equivalent sand-grain roughness height. You obtain the value that is appropriate for your model either from the literature or empirically.

For more information, see Wall Treatment for Rough Walls.

A wall boundary represents a flow impermeable boundary. For more information, see Wall.