Linearized Potential Flow Model
The Linearized Potential Flow Model node adds the equations for frequency domain aeroacoustics modeling. You here need to enter the material properties as well as the background mean flow information.
Model Inputs
In order to model the influence of the background mean flow on the propagation of the acoustic waves in the fluid, the background mean flow temperature T0, absolute pressure p0, and velocity field u0 need to be defined.
Select User defined (the default), Common model input, or a variable defined by a flow simulation performed using the CFD Module. By default, they are set to the quiescent background conditions of air. All the background flow parameters can also be constants or analytical expressions functions of space. When the Background Potential Flow Coupling multiphysics is used to couple The Compressible Potential Flow Interface to the acoustics domain, the required input field will appear locked (grayed out).
Details about the Model Input and the Default Model Inputs are found in the Global and Local Definitions chapter of the COMSOL Multiphysics Reference Manual.
It is important that the velocity field is a solution to a compressible potential flow simulation. It has to be an irrotational and inviscid flow, for example, a constant flow field u0 or a solution modeled with The Compressible Potential Flow Interface. Any other type of flow yields unphysical solutions for this formulation of the governing equations.
Enter User defined values for the Background mean flow temperature T0 (SI unit: K), Background mean flow pressure p0 (SI unit: Pa), and Background mean flow velocity u0 (SI unit: m/s). The defaults are 293.15 K, 1 atm, and 0 m/s, respectively.
Note that the Background mean flow density and Speed of Sound also need to be defined or entered in the Fluid Properties section below.
Fluid Properties
The default values for the Density ρ0 (SI unit: kg/m3) and the Mean flow speed of sound c0 (SI unit: m/s) are taken From material. For User defined, enter other values or expressions.
Coupling the flow from The Compressible Potential Flow Interface interface to the linearized potential flow model can be set up using the Background Potential Flow Coupling found under the Multiphysics Couplings node. The feature appears when both physics interfaces are present in a model.
Material discontinuities, that is jumps in the material properties, are not handled by the interface. A jump due to the presence of a shear layer that separates a stream from the free velocity field is handled using the Vortex Sheet condition.