Home / Examples / Fluid Analysis [Bernoulli] / Example 4: Forced-outflow Fan

Example 4: Forced-outflow Fan

General

Fan boundary condition is applied to the model used in the tutorial.
See Boundary Condition of Fluid Analysis for the details of the fan boundary condition.
Unless specified in the list below, the default conditions will be applied.

Results will vary depending on Femtet version and the PC environment.

Analysis Space

Item	Settings
Analysis Space	3D
Model Unit	mm

Analysis Condition

Item	Tab	Settings
Solver	Solver Selection	Fluid Analysis [Bernoulli]
Analysis Type	Fluid Analysis	Steady-state Analysis
Meshing Setup	Mesh	General Mesh Size: 6 [mm]

Model

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
3/Solid	Flow_path	000_Air(*)
4/Solid		007_Fe *

* Available from the material DB

Boundary Condition

Boundary Condition Name/Topology

Tab

Boundary Condition Type

Settings

Inlet/Edge

Fluid

Inlet

Natural Inflow

Outlet/Face

Fluid

Outlet

Forced Outflow
Fan

PQ Characteristics

Number	Volumetric Flow Rate Q [m3/s]	Differential Pressure P [Pa]
1	0	0.2
2	2e-4	0

Results

The figure below is the contour of [total pressure] field.

The integration results at the inlet and outlet boundary faces are shown as well. (Selected faces are integrated by the right-click menu)

The total pressure is nearly zero under the natural inflow boundary. Under the forced-outflow fan boundary, it is -0.1034 [Pa] which is calculated from the PQ characteristics.

The tables of the volumetric flow rate and the pressure loss are as follows.

The differential pressure is calculated with PQ characteristics from the table of the volumetric flow rate of the outlet boundary as follows.
P = 0.2 - 0.2/2e-4 * 9.731e-5 = 0.1027

The calculation result matches with the values in the contour of the total pressure and in the table of the pressure loss.

The PQ characteristics and the working point (volumetric flow rate:Q and pressure loss: P) are plotted as below.

It is confirmed that the working point is on the PQ characteristics curve.

For reference, the flow-rate dependent curve of the pressure loss is also shown below.
The curve is calculated for the volumetric flow rate between 2.5e-5 and 1.5e-4 using the velocity fixed boundary. The two curves are crossing at the operating point.

The flow-rate dependent curve of the pressure loss is obtained in the attached project [analysis model_reference].
･Open the project file.
･Change to the analysis model of [analysis model_reference].
･Perform the parametric analysis.
･The results of the flow rate and the pressure loss are saved in a csv file.