Surface parts can also be used as distributed resistance regions. Applications include very thin baffles, perforated plates, and any type of very thin obstruction that would be very cumbersome and computationally expensive to model as a volume.
Unlike volumes, Surface parts cannot be used to simulate pressure drop within the plane of the object (secondary losses). All pressure loss will be in the direction normal to the plane, and the flow will be constrained to be normal to the surface. To allow for secondary-direction flow through a resistance, a volume must be used for the resistance region.
A nodal reorganization is performed during startup processing to ensure connectivity between the distributed resistance region and the surrounding mesh. This means that it is not possible to change the mesh and continue the analysis from a saved iteration. If the mesh is changed in a model containing a distributed resistance surface part, the analysis must be started back at the beginning (iteration 0).
It is very important that the fluid mesh between the edge of a floating resistance surface and the neighboring wall have at least a single row of nodes between them. If no nodes exist in this region, an error will be issued:
Distributed resistance surface parts can be planar or arbitrarily shaped. The flow direction will always be locally normal to the surface part. Note that there are limitations to the shape of a surface part. Very high curvature surfaces are not suitable for use as distributed resistances, and an error may be given.
Multiple resistance surface parts cannot be joined together to form a “composite” resistance region, and cannot touch other surface parts. A resistance must be composed of a single surface part. Surface parts that share an edge will cause an error in the analysis processing: