The Interior Normal Velocity sets up an interior source that can be used to model a thin vibrating structure, for example, a loudspeaker diaphragm. Add this node from the Interior Conditions submenu. This condition is only available when the Stabilized formulation, in the Stabilization section, is turned off.

The pressure is discontinuous across this boundary. Use the up and down version of the postprocessing variables to visualize quantities on the two sides of the boundary, for example, the up side total pressure is pabe.p_t_up.

Select a Type: Velocity (the default) or Normal velocity.

Select Show physics symbols to show the normal direction as a symbol (red arrow) in the Graphics window (selected per default).