The Fluid Flow branch ()has a number of subbranches to describe momentum transport. The main focus of this physics area is to model fluids transported in pipe networks in 2D and 3D space, calculating velocity, flow rate, and pressure drops. Pipe flow including heat and mass transfer can also be modeled.

The Pipe Flow Interface (), found under the Single-Phase Flow branch () when adding a physics interface, is used to model incompressible and weakly compressible fluid flow in piping systems. The equations that are solved are 1D equations that live on 2D boundary segments or 3D edge segments.

The Nonisothermal Pipe Flow Interface (), found under the Nonisothermal Flow branch () when adding a physics interface, solves a temperature equation together with the equations for compressible flow.

The Water Hammer Interface (), found under the Fluid Flow > Single-Phase Flow branch () when adding a physics interface, has the equations and boundary conditions for modeling rapid pressure transients in a pipe systems.