Interior Fan
The Interior Fan condition represents interior boundaries where a fan condition is set using a fan pressure curve to avoid an explicit representation of the fan. The Interior Fan defines a boundary condition on a slit for laminar flow. That means that the pressure and the velocity can be discontinuous across this boundary.
One side represents a flow inlet; the other side represents the fan outlet. The fan boundary condition ensures that the mass flow rate is conserved between its inlet and outlet:
This boundary condition acts like a Pressure Conditions boundary condition on each side of the fan. When a pressure curve is used, the pressure at the fan outlet is fixed so that the mass flow rate is conserved. On the fan inlet the pressure is set to the pressure at the fan outlet minus the pressure drop induced by the fan. The pressure drop is defined from the static pressure curve, and is usually a function of the flux. When the flux is prescribed the pressure at the inlet and at the outlet are set so that the flux obtains the desired value.
To define a fan boundary condition on an exterior boundary, the Fan condition should be used instead.
Flow Direction
The Flow direction can be defined by selecting Along normal vector or Opposite to normal vector. This defines which side of the boundary is the fan’s inlet and which side is the fan’s outlet.
Select Prescribe flow direction, to enforce the flow direction of the fluid when it enters the domain located at the fan outlet.
•
For Normal flow it sets the tangential velocity component to zero.
•
For Swirl flow (which is available for 3D or 2D axisymmetric when the Swirl flow check box in the Physical Model section is selected) it specifies a swirl flow on the downstream side of the fan based on the Rotation axis base point rbp, Revolutions per time f, Rotational direction and Swirl ratio csf.
•
For User defined an Inflow velocity direction du (dimensionless) should be specified. The magnitude of du does not matter, only the direction. du must point into the domain.
Parameters
All the settings for this section except Prescribe flux are the same as for the Fan node. See Static pressure curve, linear and Static pressure curve, data for details.
When Prescribe flux is selected, define the Prescribed flux V0,pf (SI unit m3/s, default value 0.01 m3/s).
Turbulence Conditions on Fan Outlet
When the Turbulence model has transport equations for the turbulent kinetic energy, k, and turbulent dissipation rate, ε, specific dissipation rate, ω, or turbulent relative fluctuations, ζ, the values of the Turbulent kinetic energy, Turbulent relative fluctuations (for the v2-f turbulence model) and the Turbulent dissipation rate or Specific dissipation rate on the downstream side of the fan should be specified. If Include transition modeling is active for the SST turbulence model, the option to specify Intermittency is also available. Alternatively, the Reference velocity scale can be used to specify default values.
After a boundary has been selected, an arrow displays in the Graphics window to indicate the selected flow direction. If the selection changes, the arrow can be updated by clicking any node in the Model Builder and then clicking the Interior fan node again to update the Graphics window.
Fan Defined on an Interior Boundary
The Interior Fan feature uses the flux across the boundary selection. This feature is not designed to be used on disjoint selections. If the model includes several fans on boundaries that are not connected, it is good practice to use different Fan or Interior Fan features with connected boundaries.