Acoustic-Thermoviscous Acoustic Boundary
The Acoustic-Thermoviscous Acoustic Boundary coupling () is used to couple a thermoviscous acoustics domain to a pressure acoustics domain (in both frequency and time domain). This includes both the FEM-based acoustics interfaces and the BEM-based acoustics interface. As it is only necessary to solve the full detailed thermally conducting and viscous model near walls in the boundary layer region, it makes sense to switch to classical pressure acoustics outside this region. This approach saves a lot of memory and solution time due to the reduced number of degrees of freedom.
Note that, when using the coupling at places where pressure acoustics and thermoviscous acoustics interact at a common wall, the coupling becomes unphysical if no-slip and isothermal conditions are used in the thermoviscous domain. The reason is that the conditions at the wall must match between the physics. The coupling assumes adiabatic behavior and normal-stress coupling only, which is not valid in the thermal and viscous boundary layers. The introduced error depends on the model size and the thickness of the acoustic boundary layer. If it makes physical sense then, use the slip and adiabatic options on that specific wall (add an extra wall boundary condition). In general using the coupling in a cross section of a waveguide will not be physically correct if the boundary layer effects are of importance.
The coupling prescribes continuity in the total normal stress (dynamic condition) and the total normal acceleration for the mechanical part (kinematic condition). An adiabatic condition is prescribed for the total temperature to match the physical assumptions of the pressure acoustics formulation. The coupling reads
The thermoviscous acoustic pressure variable is pt and the pressure acoustic pressure is here denoted for clarity.
Settings
See Settings for further details about Label and Name.
The default Name (for the first multiphysics coupling feature in the model) is atb1.
Coupled Interfaces
This section defines the physics involved in the multiphysics coupling. The Acoustics and Thermoviscous Acoustics lists include all applicable physics interfaces. See the Coupled Interfaces in Acoustic-Structure Boundary for details.