The Linearized Euler, Transient Interface includes so-called
absorbing layers, also often referred to as
sponge layers. The layers work by combining three techniques: a scaling system, damping, and a simple nonreflecting conditions.
The layers are set up by adding the Absorbing Layer under the
Definitions node. This adds a special scaled system. The scaling effectively slows down the propagating waves and ensures that they “align up” (normal) toward the outer boundary. This means that the waves will hit the outer boundary in a closer to normal direction. Damping in the form of artificial numerical viscosity, is automatically applied in the layer in a matched manner (increasing from zero at the boundary to the physical domain). The artificial viscosity attenuates or damps high-frequency components of the wave in the layer. The amount of damping is controlled under the
Damping Parameters for Absorbing Layers section at the main physics level. Finally, at the outer boundary of the layer add a simple
Acoustic Impedance (Isentropic) boundary condition, which will work well to remove all remaining waves, as normal incidence has been ensured.
For the Absorbing Layers select the
Type (Cartesian, cylindrical, spherical, or user defined) under the
Geometry section. Enter values for the
Physical Width and
Pole Distance under the
Scaling section.