Surface Normal Fixed Value - Boundary Conditions

Surface Normal Fixed Value boundary condition is primarily used when a specific value needs to be assigned to a vector field variable (e.g., velocity) and only the component normal to the boundary surface is known. This condition sets a fixed value for the component of the field that is perpendicular to the boundary surface, while tangential components are set to zero.

The advantage of using Surface Normal Fixed Value instead of a Fixed Value is the fact that is independent of the local mesh boundary orientation.

For the user’s convenience in SimFlow, a positive value will indicate the inflow into the domain, which is opposite to the OpenFOAM notation. In OpenFOAM, the provided value just scales the surface normal vector, which by definition points outside the fluid domain.

Surface Normal Fixed Value boundary condition is one of the most often used, especially in aerodynamics simulations, where the user needs to specify the inlet velocity.

The definition of boundary conditions in SimFlow is both straightforward. To define Surface Normal Fixed Value boundary condition on the patch, the proper option must be selected from the drop-down menu in Boundary Conditions tab - Figure 1

The User needs to define:
Reference Value - mean value of the field, for example, mean velocity at the boundary [\(m/s\)]

In this section, we propose boundary conditions that are alternative to Surface Normal Fixed Value. While they may fulfill similar purposes, they might be better suited for a specific application and provide a better approximation of physical world conditions.