
Once the fan zone has been identified (in the Boundary Conditions panel), you will set all modeling inputs for the fan in the Fan panel (Figure 7.20.1), which is opened from the Boundary Conditions panel (as described in Section 7.1.4).
Inputs for a fan are as follows:
Identifying the Fan Zone
Since the fan is considered to be infinitely thin, it must be modeled as the interface between cells, rather than a cell zone. Thus the fan zone is a type of internal face zone (where the faces are line segments in 2D or triangles/quadrilaterals in 3D). If, when you read your grid into FLUENT, the fan zone is identified as an interior zone, use the Boundary Conditions panel (as described in Section 7.1.3) to change the appropriate interior zone to a fan zone.
Define Boundary Conditions...
Once the interior zone has been changed to a fan zone, you can open the Fan panel and specify the pressure jump and, optionally, the swirl velocity.
Defining the Pressure Jump
To define the pressure jump, you will specify a polynomial, piecewiselinear, or piecewisepolynomial function of velocity, a userdefined function, or a constant value. You should also check the Zone Average Direction vector to be sure that a pressure rise occurs for forward flow through the fan. The Zone Average Direction, calculated by the solver, is the faceaveraged direction vector for the fan zone. If this vector is pointing in the direction you want the fan to blow, do not select Reverse Fan Direction; if it is pointing in the opposite direction, select Reverse Fan Direction.
Polynomial, PiecewiseLinear, or PiecewisePolynomial Function
Follow these steps to set a polynomial, piecewiselinear, or piecewisepolynomial function for the pressure jump:
When you define the pressure jump using any of these types of functions, you can choose to limit the minimum and maximum velocity magnitudes used to calculate the pressure jump. Enabling the Limit Polynomial Velocity Range option limits the pressure jump when a Min Velocity Magnitude and a Max Velocity Magnitude are specified.

The values corresponding to the
Min Velocity Magnitude and the
Max Velocity Magnitude do not limit the flow field velocity to this range. However, this range does limit the value of the pressure jump, which is a polynomial and a function of velocity, as seen in Equation
7.201. If the calculated normal velocity magnitude exceeds the
Max Velocity Magnitude that has been specified, then the pressure jump at the
Max Velocity Magnitude value will be used. Similarly, if the calculated velocity is less than the specified
Min Velocity Magnitude, the pressure jump at the
Min Velocity Magnitude will be substituted for the pressure jump corresponding to the calculated velocity.

You also have the option to use the massaveraged velocity normal to the fan to determine a single pressurejump value for all faces in the fan zone. Turning on Calculate PressureJump from Average Conditions enables this option.
Constant Value
To define a constant pressure jump, follow these steps:
You can follow the procedure below, if it is more convenient:
UserDefined Function or Boundary Profile
For a userdefined pressurejump function or a function defined in a boundary profile file, you will follow these steps:
See the separate UDF Manual for information about userdefined functions, and Section 7.26 for details about boundary profile files.
Example: Determining the Pressure Jump Function
This example shows you how to determine the function for the pressure jump. Consider the simple twodimensional duct flow illustrated in Figure 7.20.3. Air at constant density enters the 2.0 m 0.4 m duct with a velocity of 15 m/s. Centered in the duct is a fan.
Assume that the fan characteristics are as follows when the fan is operating at 2000 rpm:
(m /s)  (Pa) 
25  0.0 
20  175 
15  350 
10  525 
5  700 
0  875 
where is the flow through the fan and is the pressure rise across the fan. The fan characteristics in this example follow a simple linear relationship between pressure rise and flow rate. To convert this into a relationship between pressure rise and velocity, the crosssectional area of the fan must be known. In this example, assuming that the duct is 1.0 m deep, this area is 0.4 m , so that the corresponding velocity values are as follows:
(m/s)  (Pa) 
62.5  0.0 
50.0  175 
37.5  350 
25.0  525 
12.5  700 
0  875 
The polynomial form of this relationship is the following equation for a line:
(7.204) 
Defining Discrete Phase Boundary Conditions for the Fan
If you are modeling a discrete phase of particles, you can set the fate of particle trajectories at the fan. See Section 22.13 for details.
Defining the Fan Swirl Velocity
If you want to set tangential and radial velocity fields on the fan surface to generate swirl in a 3D problem, follow these steps:

You must use SI units for all fan swirl velocity inputs.

Polynomial Function
To define a polynomial function for tangential or radial velocity, follow the steps below:
Constant Value
To define a constant tangential or radial velocity, the steps are as follows:
You can follow the procedure below, if it is more convenient:
UserDefined Function or Boundary Profile
For a userdefined tangential or radial velocity function or a function contained in a boundary profile file, follow the procedure below:
See the separate UDF Manual for information about userdefined functions, and Section 7.26 for details about boundary profile files.