Inlet
The Inlet node adds a selection of boundary conditions that describe inlets in fluid-flow simulations.
Liquid Boundary Condition
Select a Liquid boundary conditionVelocity (the default), Pressure, or Fully developed flow.
Velocity
For Velocity click the Normal inflow velocity (the default) or Velocity field buttons.
For Normal inflow velocity enter a value or expression for U0 (SI unit: m/s).
For Velocity field specify that the velocity at the boundary is equal to a given u0 (SI unit: m/s) and enter the components in the matrix:
Pressure
This condition specifies the normal stress which in most cases is approximately equal to the pressure. Enter the Pressure p0 (SI unit: Pa) at the boundary. The default is 0 Pa. Enter a relative pressure value in p0 (SI unit: Pa). Or if the reference pressure pref defined at the physics interface level is equal to 0 Pa, enter an absolute pressure in p0.
The Suppress backflow check box is selected by default. This option adjusts the inlet pressure, , locally in order to reduce the amount of fluid exiting the domain through the boundary. If suppress backflow is deselected, the inlet boundary can become an outlet depending on the pressure field in the rest of the domain.
Flow direction controls in which direction the fluid enters the domain.
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For Normal flow (the default) it prescribes zero tangential velocity component.
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For User defined define an Inflow velocity direction, du (dimensionless). The magnitude of du does not matter, only the direction. du must point into the domain.
Fully Developed Flow
The Fully developed flow option adds contributions to the inflow boundary, which force the flow toward the solution for a fully developed channel flow. The channel can be thought of as a virtual extrusion of the inlet cross section. The velocity is defined by the boundary condition of the adjacent boundary in the model.
The boundary conditions for the virtual inlet channel are inherited from the boundaries adjacent to the inlet channel. Virtual boundaries adjacent to walls (except slip walls) are treated as no-slip walls. Virtual boundaries adjacent to any other type of boundary are treated as slip-walls (or equivalently as symmetry boundaries).
Select a Fully developed flow option — Average velocity (the default), Flow rate, or Average pressure.
The Fully developed flow option adds contributions to the inflow boundary, which force the flow toward the solution for a fully developed channel flow.
Select an option to control the flow rate at the inlet:
For Average velocity enter Uav.
Flow rate, V0. Two-dimensional models also require an Entrance thickness, Dz, which is the out-of-plane thickness of the extruded entrance channel.
Average pressure, Pav. Observe that Pav is the average pressure on the inflow boundary.
Fully developed inflow can be used in conjunction with the turbulence models. No additional inputs are required for the turbulence variables. They are instead solved for on the inlet boundary to be consistent with the fully developed flow profile.
A fully developed flow boundary cannot be adjacent to any Interior Wall feature
Gas Boundary Condition
These settings are the same as for Wall. See Gas Boundary Condition. The only difference is that Gas concentration is the default.
Turbulence Conditions
This section is available for Bubbly Flow, Turbulent Flow interfaces. No additional inputs are required for Fully developed flow.
No additional inlet conditions are required for the algebraic turbulence models: Algebraic yPlus and L-VEL.
For the Bubbly Flow, Spalart-Allmaras interface, a value or expression for the Undamped turbulent kinematic viscosity υ0 should be specified. The default value is 3*bf.nul.
For transport-equation turbulence models, apart from Spalart–Allmaras, the following settings are available under the Specify turbulence length scale and intensity option (see Table 3-3 for the default values):
For the v2-f turbulence model, the additional choice between Isotropic turbulence and Specify turbulence anisotropy appears. For Specify turbulence anisotropy, a value for the turbulent relative fluctuations at the inlet, ζ0, may be specified. When Specify turbulence variables is selected, values or expressions for the dependent turbulence variables should be defined. Availability is based on the physics interface and the boundary condition chosen.
The turbulent length scale LT and turbulence intensity IT are related to the turbulence variables, see Theory for the Turbulent Flow Interfaces.
See Inlet in the Single-Phase Flow interfaces