Boundary conditions

Once the geometry of the control domain is defined, we have to proceed with setting the boundary conditions of the problem (access the conditions menu as shown in example 1). The conditions to be applied in this example are:

a)      Velocity field [line]

b)      Pressure field [line]

a) Velocity field [line]

The Velocity Field condition is used to fix the velocity in a surface to the velocity field given in the Data > Initial Data >RANSOL menu (fields Initial_Velocity_X, Initial_Velocity_Y and Initial_
Velocity_Z
). Those fields can define a space-time-variable dependant function and thus the Velocity Field condition can be used to specify a variable inflow. In order to do this, the corresponding Fix_Field flag has to be marked.

It is also possible to fix the Velocity (during the run) to the initial value of the function given in the above mentioned entries. In order to do this, the corresponding Fix_Initial flag has to be marked.

This condition is now going to be assigned to the inflow and lateral lines of the channel. In our case, all the velocity components have to be fixed (i.e. mark Fix_Field_X and Fix_Field_Y) for the inflow lines and only the vertical component (i.e. mark Fix_Field_Y) for the lateral lines (see Figure 84). Then, the corresponding components will be fixed to its initial value.


Figure 84 Velocity Field Line conditions

b) Fix Pressure [Line]

As mentioned in example 1, in order to solve the problem, the pressure must be fixed at least in one point of the control domain (taken as reference). Here we will apply the Fix Pressure [Line] condition to the outflow lines of the domain (see Figure 85). By imposing this condition, the value of the dynamic pressure defined in the corresponding Material (Fluid) (p = p- rgz = 0 in our case) will be then assigned to this line.

Figure 85 Overview of the applied conditions