Home / How to Set Body Attribute, Material Property and Boundary Condition / Boundary Condition Tabs / Fluid Tab (Fluid Thermal tab)

Fluid Tab (Fluid Thermal tab)

Boundary conditions relating to the fluid are set on this tab. In the case of fluid-thermal coupled analysis, the fluid thermal tab is displayed.

It is in the [Edit Boundary Condition] dialog box. See [How to Set Boundary Condition].

For the general explanations of the boundary condition setting, refer to [Boundary Condition of Fluid Analysis] of Technical Note.

Setting Item

Notes

Solid Wall
Slip Wall

Sets to the wall face where there are no inflow or outflow of the fluid.

Solid Wall: Flow velocity is zero on the wall face.

Slip Wall: Flow velocity in the normal direction to the wall face is zero.

The difference between the solid wall and the slip wall is explained in [Boundary Condition of Fluid Analysis] of Technical Note.

Solid wall type is selectable.

The moving wall specifies the boundary that moves at a constant velocity or rotates at a constant angular velocity.

Click The [Moving Wall Setting] dialog box will appear.

Layer mesh of the wall surface can be set for each boundary condition.

Select [Specify for each boundary condition] and click . The [Layer Mesh Setting] dialog box will appear.

For the boundary condition in the diffusion analysis, the diffusion value must be set to the wall face.

Click to show the [Diffusion Analysis Setting [Wall Face]] dialog box.

For the free surface analysis, the contact angle on the solid surface must be set.

Click to show the [Multiphase Flow Setting [Wall Face]] dialog box.

For the fluid-thermal analysis, thermal boundary condition must be set to the wall face.

Specifying Method

Notes

Adiabatic

Be specified for the case where the heat is not lost or gained (heat flux: 0 [W/m2]).

Temperature

Sets the temperature of the wall face.

Specifying Method

Notes

Use ambient temperature

Uses the ambient temperature set on the Fluid-thermal analysis tab].

Direct Entry

Specifies temperature.

* You may set the time dependency with the weight function for transient analysis.

Select Time Dependency and click Weight Function. [Time-Weight] table will appear.
Fill in the table to set the change over time.

Heat Flux

Specifies the heat flux given to the fluid from the wall face.

Heat Transfer: Convection

Sets the heat transfer between boundary and outer environment.

The heat flux due to the heat transfer is calculated by the surface temperature θ, room (ambient) temperature θroom, and the related coefficients.

The heat transfer to the outside beyond the solid wall and the heat transfer from the fluid surface to the gas can be taken into account.

Heat Transfer: Convection Type

Setting Item	Notes
Specify coefficient of heat transfer	Specifies the value (h) can be entered directly. The heat flux from boundary to environment is h(θ-θroom)
Natural Convection (Automatic Calculation)	Calculates the heat transfer to the environment by natural convection. The heat flux from boundary to environment is calculated as below. con(θ-θroom)^(5/4) where con is automatically calculated by con = 2.51 x C x (1/L)^(1/4) C and L are given by Table 1, which are "Vertically placed board", "Horizontally placed board with the hot face up" and "Horizontally placed board with the hot face down" To use this boundary condition, the model must be oriented so that the negative Z direction points to the ground. Please note that the direction is critical for the natural convection.
Natural Convection (Direct Entry)	Calculates the heat transfer caused by natural convection. However, the coefficient con is not calculated automatically. The heat flux from the boundary to the environment is calculated with the specified coefficient con as below. con(θ-θroom)^(5/4)

Ambient Temperature Setting

Specifying Method

Notes

Use ambient temperature

Uses the ambient temperature set on the [Fluid-thermal Analysis] tab.

Direct Entry

Specifies the ambient temperature.

For transient analysis, the change of ambient temperature over time can be set by selecting Time Dependency.

By clicking Weight Function, the [Time-Weight] table will appear.

Inlet

Applied to the face where the fluid flows in.

Natural Inflow

Takes the inflow from the environment into account.

Femtet executes calculation assuming that the pressure of the environment is 0 [Pa]. The flow velocity of the inflow and the static pressure are calculated so that the total pressure becomes 0 [Pa] on the boundary condition.
If the loss coefficient (loss coefficient K) is set, the pressure loss at the inlet is taken into account, which is given by the following equation where ρ is fluid density and V is flow velocity.

See Loss Coefficient at Inlet and Outlet for Natural Flow for more details.

Forced Inflow > Specify flow velocity

Specifies the flow velocity in the normal direction to the face.

If [Direction/Distribution Input] is set, [Specify direction vector] and [Specify velocity vector] are selectable in addition to velocity.

[Specify direction vector] sets the inflow direction for the specified flow velocity on the orthogonal coordinates or cylindrical coordinates.

In this setting, unit vector is not required for the input. Normalization will be executed automatically.

[Specify velocity vector] sets the inflow velocity vector directly on the orthogonal coordinates or cylindrical coordinates.

In this setting, if cylindrical coordinates are selected, angular velocity with gravity center of the specified face can be specified.

See [How to Set Distributed Boundary Condition and Body Attribute] for the detail.

*If the direction vector and the velocity vector are in the outflow direction in relation to the normal vector of the inlet, where the inner product with normal vector is negative,

the error message [Failed to create the boundary condition data for the fluid analysis] will show up.

*The orthogonal coordinates specify vector by X, Y, Z directions in the global coordinates.

The cylindrical coordinates specify vector by radius direction, tangential direction, and axial direction with gravity center

*In the 2D axisymmetric analysis, setting of direction vector and velocity vector by the cylindrical coordinates is not allowed.

* You may set the time dependency with the weight function for transient analysis.

Select Time Dependency and click Weight Function. [Time-Weight] table will appear.
Fill in the table to set the change over time.
By setting the negative weight, the inflow can be switched to the outflow.

Forced Inflow > Specify flow rate

Specifies the volumetric flow rate in the normal direction to the face.

If [Direction/Distribution Input] is set, [Specify direction vector] is selectable in addition to the volumetric flow rate.

[Specify direction vector] sets the inflow direction for the specified volumetric flow rate on the orthogonal coordinates or cylindrical coordinates.

In this setting, unit vector is not required for the input. Normalization will be executed automatically.

*If the direction vector and the velocity vector are in the outflow direction in relation to the normal vector of the inlet, where the inner product with normal vector is negative,

the error message [Failed to create the boundary condition data for the fluid analysis] will show up.

*In the 2D axisymmetric analysis, setting of direction vector and velocity vector by the cylindrical coordinates is not allowed.

* You may set the time dependency with the weight function for transient analysis.

Forced Inflow > Specify pressure

Specifies the pressure difference with the environment.

The flow velocity of the inflow and the static pressure are calculated to specify the pressure by the total pressure.

If Use static pressure is selected, the inflow velocity is calculated to specify the pressure by the static pressure.

If the static pressure is used, the calculation may become unstable in some cases.

* You may set the time dependency with the weight function for transient analysis.

Select Time Dependency and click Weight Function. [Time-Weight] table will appear.
Fill in the table to set the change over time.

Forced Inflow > Fan

Sets the relationship of the volumetric flow rate and the differential pressure (P-Q characteristics) in the table.

, if clicked, opens [Volumetric Flow Rate Q - Differential Pressure P] Curve.

The volumetric flow rate and the differential pressure are entered in the table.

When setting, the first data must have the volumetric flow rate of 0[m3/s], and the last data must have the differential pressure of 0[Pa].

The analysis is executed with the volumetric flow rate where the rising pressure and the pressure loss in the analysis domain become almost equal.

To take the swirl in the downstream of the axial flow fan into account, teh number of rotations and the slip factor are required to set.

See Boundary Condition of Fluid Analysis of Technical Note for more details.

Fluid Temperature

Sets the fluid temperature for the incoming fluid in the fluid-thermal analysis.

Specifying Method

Notes

Use ambient temperature

Uses the ambient temperature set on the [Fluid-thermal Analysis] tab.

Direct Entry

Specifies temperature.

* You may set the time dependency with the weight function for transient analysis.

Select Time Dependency and click Weight Function. [Time-Weight] table will appear.
Fill in the table to set the change over time.

Turbulent Flow Setting

Sets the turbulent flow energy and the energy dissipation rate if turbulent flow is selected in the analysis condition.

, if clicked, opens the [Turbulent Flow Setting] dialog box.

Diffusion Analysis Setting

Sets the diffusion value for the incoming fluid if the diffusion analysis is selected in the analysis condition.

, if clicked, opens the [Diffusion Analysis Setting] dialog box.

Multi-Phase Flow Setting

Sets the phase for the incoming fluid if the free surface analysis is selected in the analysis condition.

, if-clicked, open the [Multiphase Flow Setting[Inflow]] dialog box.

Outlet

Applied to the face where the fluid flows out.

Natural Outflow

Takes the outflow to the environment into account.

Femtet executes calculation assuming that the pressure of the environment is 0 [Pa]. The outflow velocity is calculated so that the static pressure becomes 0 [Pa] on the boundary condition.

If the loss coefficient (loss coefficient K) is set, the pressure loss at the outlet is taken into account, which is given by the following equation where ρ is fluid density and V is flow velocity.

See Loss Coefficient at Inlet and Outlet for Natural Flow for more details.

Forced Outflow > Specify flow velocity

Specifies the flow velocity in the normal direction to the face.

* You may set the time dependency with the weight function for transient analysis.

Select Time Dependency and click Weight Function. [Time-Weight] table will appear.
Fill in the table to set the change over time.

Forced Outflow > Specify flow rate

Specifies the volumetric flow rate normal direction to the face.

* You may set the time dependency with the weight function for transient analysis.

Select Time Dependency and click Weight Function. [Time-Weight] table will appear.
Fill in the table to set the change over time.

Forced Outflow > Specify pressure

Specifies the pressure difference with the environment by the negative static pressure.

The outflow velocity is calculated so that the static pressure reaches the specified pressure on the boundary condition.

* You may set the time dependency with the weight function for transient analysis.

Select Time Dependency and click Weight Function. [Time-Weight] table will appear.
Fill in the table to set the change over time.

Forced Outflow Fan

Sets the relationship of the volumetric flow rate and the differential pressure (P-Q characteristics) in the table.

, if clicked, opens [Volumetric Flow Rate Q - Differential Pressure P] Curve.

The volumetric flow rate and the differential pressure are entered in the table.

When setting, the first data must have the volumetric flow rate of 0 [m3/s], and the last data must have the differential pressure of 0 [Pa].

The analysis is executed with the volumetric flow rate where the rising pressure and the pressure loss in the analysis domain become almost equal.

See Boundary Condition of Fluid Analysis of Technical Note for more details.

Inlet/Outlet

Applies to the face where it is not known if the fluid flows in or flows out.

Natural Inflow/Outflow

No items to set.
An inflow/outflow to the environment is taken into account.

Femtet executes calculation assuming that the pressure of the environment is 0 [Pa].

At the inflow, the flow velocity of the inflow and the static pressure are calculated so that the total pressure becomes 0 [Pa] on the boundary condition.

At the outflow, the fluid velocity of the outflow is calculated so that the static pressure becomes 0 [Pa] on the boundary condition.

Fluid Temperature

Sets the fluid temperature for the incoming fluid in the fluid-thermal analysis.

For details, see the explanations of the inflow above.

Turbulent Flow Setting

Sets the turbulent flow energy and the energy dissipation rate if turbulent flow is selected in the analysis condition.

, if clicked, opens [Turbulent Flow Setting] dialog box.

Diffusion Analysis Setting

Sets the value of diffusion for the incoming fluid if diffusion analysis is selected in the analysis condition.

, if clicked, opens [Diffusion Analysis Setting] dialog box.

Inlet/Outlet Pairing

Connects the inlet and the outlet of the distant faces.
The boundary flow velocity is given so as to have the same flow rate at the inflow and outflow faces.

The boundary temperature and the boundary turbulent flow rate are given so as to have the same outflow rate and inflow rate.

Pairing of inlet and outlet is required. See [Inlet/Outlet Pair Boundary] for the details.

Inflow Face/Outflow Face

Specifies the face either for inflow or outflow.

Inlet/Outlet Pair Type

Selectable when the inlet face is set.

Specify Flow Velocity

Specifies the flow velocity in the normal direction to the face.

If [Direction/Distribution Input] is set, [Specify direction vector] and [Specify velocity vector] are selectable in addition to velocity.

[Specify direction vector] sets the inflow direction for the specified flow velocity on the orthogonal coordinates or cylindrical coordinates.

In this setting, unit vector is not required for the input. Normalization will be executed automatically.

[Specify velocity vector] sets the inflow velocity vector directly on the orthogonal coordinates or cylindrical coordinates.

In this setting, if cylindrical coordinates are selected, angular velocity with gravity center of the specified face can be specified.

See [How to Set Distributed Boundary Condition and Body Attribute] for the detail.

*If the direction vector and the velocity vector are in the outflow direction in relation to the normal vector of the inlet, where the inner product with normal vector is negative,

the error message [Failed to create the boundary condition data for the fluid analysis] will show up.

*The orthogonal coordinates specify vector by X, Y, Z directions in the global coordinates.

The cylindrical coordinates specify vector by radius direction, tangential direction, and axial direction with gravity center

*In the 2D axisymmetric analysis, setting of direction vector and velocity vector by the cylindrical coordinates is not allowed.

* You may set the time dependency with the weight function for transient analysis.

Select Time Dependency and click Weight Function. [Time-Weight] table will appear.
Fill in the table to set the change over time.

Specify flow rate