Boundary conditions

Once we have defined the geometry of the control volume, it is necessary to set the boundary conditions of the problem (see Figure 2). The only conditions to specify here is Fix Velocity.

 

Figure 2 Open condition assignment window and icon

Fix Velocity condition is used to impose the velocity. Available entry fields store the velocity components given in global axes and the flags Fix_X, Fix_Y and Fix_Z allows to indicate if the corresponding components have to be fixed or not.

Remark:

Entry fields will only be available in the corresponding Fix field is on.

For this example this condition is going to be assigned to the surface swept by the flow (see Figure 3). In our case, the X-component of the velocity vector will be set to 1.0 m/s, and the Y and Z component to zero. Then, all the velocity components have to be fixed to the specified value (i.e. mark Fix_X, Fix_Y and Fix_Z, see Figure 3).

Figure 3 Fixed velocity surface

 

Remark:

Note that in most of the cases it is strongly necessary to fix the pressure in at least one point of the domain (taken as reference). However, if this is not done (as in this example) Tdyn performs some controls that allow obtaining a solution of the problem.

If no reference for the pressure is given, node 0 will be used as reference (null pressure).