8.1.2 Step 1: Define Your Problem

The first step in creating a UDF and using it in your ANSYS FLUENT model involves defining your model equation(s).

Consider the elbow duct illustrated in Figure  8.1.1. The domain has a velocity inlet on the left side, and a pressure outlet at the top of the right side.

Figure 8.1.1: The Mesh for the Elbow Duct Example

A flow field in which a constant $x$ velocity is applied at the inlet will be compared with one where a parabolic $x$ velocity profile is applied. The results of a constant velocity (of 0.1 m/s) at the inlet are shown in Figures  8.1.2 and 8.1.3.

Figure 8.1.2: Velocity Magnitude Contours for a Constant Inlet $x$ Velocity

Figure 8.1.3: Velocity Vectors for a Constant Inlet $x$ Velocity

Now suppose that you want to impose a non-uniform $x$ velocity to the duct inlet, which has a parabolic shape. The velocity is 0 m/s at the walls of the inlet and 0.1 m/s at the center.

To solve this type of problem, you can write a custom profile UDF and apply it to your ANSYS FLUENT model.