The Acoustic Streaming Domain Coupling () is a multiphysics coupling from an acoustic interface to a fluid flow (CFD) model, used to add the domain source contributions necessary to model an acoustic streaming flow. The multiphysics coupling should be used in combination with the Acoustic Streaming Boundary Coupling to ensure that all sources are modeled.

See Settings for further details about Label and Name.

The default Name (for the first multiphysics coupling feature in the model) is asdc1.

This section defines the physics involved in the multiphysics coupling. The multiphysics interface couples a Source acoustic interface to a Destination single-phase fluid flow interface. The acoustic interface can be either Pressure Acoustics, Frequency Domain or Thermoviscous Acoustics, Frequency Domain. In the Pressure Acoustics, Frequency Domain interface it cannot couple to a Poroacoustics, Narrow Region Acoustics, or Anisotropic Acoustics domain. The fluid flow interface should be a Single-Phase Flow interface, but it cannot couple to a Porous Medium domain. The interface can couple to a turbulent flow interface but it is advised to take extra caution since the derivation of the source terms does not take turbulent flow into consideration. For a mathematically consistent formulation, the coupling is typically to the Creeping Flow or the Laminar Flow interface.

Choose to select the Subtract Lagrangian energy density options (selected per default) to subtract the Lagrangian energy density from the momentum flux tensor. The Lagrangian energy density does not induce streaming flow u2 since it results in a pure gradient force; however, it does induce a gradient in the streaming (time averaged) pressure field p2. Subtracting the Lagrangian energy density can make the simulation converge more easily on a coarser numerical mesh. The Lagrangian energy density has a large numerical value compared to the other terms even though it does not induce streaming. Note that because the Lagrangian energy density is subtracted, the resulting pressure calculated in the flow module is not the correct physical pressure, but the velocity field is correct. The Lagrangian energy variable asdc1.Lac can be added to the pressure p2 in postprocessing to get the correct pressure.

The forces applied on the fluid flow depends on the derivatives of the acoustic fields. Therefore, it is recommended to use quadratic element order for the acoustic pressure, and when coupling to Thermoviscous Acoustics, Frequency Domain use cubic element order for the acoustic velocity and temperature.