Aeroacoustic Flow Source
The Aeroacoustic Flow Source feature is used to set up aeroacoustic flow-induced noise sources in the pressure acoustics model. The feature is best used when coupling to a Fluid Flow model (LES, DES, or RANS-EVM SST-SAS) or to The Imported Fluid Flow Interface, using the Aeroacoustic Flow Source Coupling and the dedicated Transient Mapping study. The feature only exists in 3D. The feature can also be used with user-defined expressions for a Lighthill like source expressed in terms of a stress tensor Tij (SI unit: N/m2). Add this node from the More submenu.
The required Fluid Flow turbulence models to use are:
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Large Eddy Simulation (LES),
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Detached Eddy Simulation (DES), or
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The RANS-EVM SST model with scale-adaptive simulation (SAS)
Aeroacoustic Flow Source
Select the Acoustic analogy as Lighthill (the default) or Aeroacoustic wave equation. The Domain Section and the Boundary Selection should match the corresponding selections made in the Aeroacoustic Flow Source Coupling multiphysics node.
When the multiphysics coupling is used, the Stress tensor (T), Normal mass flow on exterior boundaries (mn), or the Flow pressure variation, second time derivative () field are automatically coupled (appear grayed out).
If no multiphysics coupling is used, then enter user-defined expressions for the fields. The user-defined expressions correspond to the Fourier components of the different flow sources terms.
Window Function
When the aeroacoustic flow source region is compact, that is, it is not selected in the entire acoustic domain, it can be necessary to use a window function to truncate the aeroacoustic source terms in a consistent manner. This can often be the case as it is computationally expensive to resolve the flow source in its full spatial extent.
To use a window function click and select Use window function, the default expression is 1 which corresponds to not having a window. When selected enter an expression for the Window function w(x). The function should be a spatially varying expression that smoothly truncates the computational domain. Example of window or truncation functions are given in Ref. 76 and Ref. 77.
Cavity Flow Noise tutorial available in the COMSOL Application Gallery at: www.comsol.com/model/cavity-flow-noise-105021
Best practices for modeling with the Aeroacoustic Flow Source and the associated multiphysics functionality is presented in the Modeling with the Aeroacoustic Flow Source: Flow-Induced Noise section.