The Linearized Navier–Stokes, Boundary Mode (lnsbm) interface (), found under the Acoustics>Aeroacoustics branch () when adding a physics interface, is used to compute and identify propagating and nonpropagating modes in waveguides and ducts in the presence of any stationary isothermal or nonisothermal background mean-flow. The interface performs a boundary mode analysis on a boundary, inlet, or cross section of the waveguide. The interface considers all thermal and viscous loss effects and the interaction with the background flow. This includes the acoustic boundary layer losses, if necessary. The interface exists in 3D and 2D axisymmetric geometries and applies to boundaries.

When this physics interface is added, these default nodes are also added to the Model Builder — Linearized Navier–Stokes Model, Wall, and Initial Values. For axisymmetric components, an Axial Symmetry node is also added. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions and sources. You can also right-click Linearized Navier–Stokes, Boundary Mode to select physics features from the context menu.

The Label is the default physics interface name.

The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.

The default Name (for the first physics interface in the model) is lnsbm.