Aeroacoustic Flow Source Coupling
The Aeroacoustic Flow Source Coupling () is a unidirectional multiphysics coupling between an LES (large eddy simulations) or DES (detached eddy simulation) Fluid Flow interface and the Aeroacoustic Flow Source feature in the Pressure Acoustics, Frequency Domain interface.
The coupling feature should be solved for in a separate study using the dedicated Transient Mapping () study. This step will map necessary data from the CFD source mesh to an acoustics mesh. Following the Transient Mapping, a separate Time to Frequency FFT study has to be used to transform the flow source data from the time domain to the frequency domain. Then the Pressure Acoustics, Frequency Domain model is solved.
For more details about theory and setting up an aeroacoustic model with flow-induced noise, see Modeling with the Aeroacoustic Flow Source: Flow-Induced Noise.
Settings
See Settings for further details about Label and Name.
The default Name (for the first multiphysics coupling feature in the model) is afsc1.
Domain Selection
Select the domains where the Lighthill stress tensor is computed, mapped to the acoustic mesh, and used in the Aeroacoustic Flow Source feature as a source term.
Boundary Selection
If the Acoustic analogy option is set to Lighthill (see below), select boundaries where the normal mass flow is mapped. This corresponds to sources generated by moving/vibrating boundaries in the flow simulation. If all boundaries are rigid, no boundary selection is necessary.
Coupled Interfaces
Select the Source and Destination physics. The source can only be an LES or DES fluid-flow physics interface and the destination the Pressure Acoustics, Frequency Domain interface.
Aeroacoustic Flow Source
Select the Acoustic analogy, used for the computational aeroacoustics (CAA) simulation, as Lighthill (the default) or Aeroacoustic wave equation. For the coupling to work, the Acoustic analogy selection in the Aeroacoustic Flow Source has to match the options selected in the multiphysics coupling.
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For Lighthill, select Include excess pressure effects or Include viscous stress. The excess pressure option adds corrections to the Lighthill stress tensor that stem from nonlinear effects, that is, where the linear pressure-density constitutive relation does not hold. The viscous stress option adds the viscous stress components of the tensor. These are, for example, necessary for models with small dimensions where damping can be important. The data mapped/coupled to the Aeroacoustic Flow Source feature will contain the necessary 6 elements of the Lighthill stress tensor (as the tensor is symmetric). The full tensor is used in the subsequent acoustic simulation.
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For Aeroacoustic wave equation, only the scalar data associated with the second time derivative of the pressure is mapped/coupled to the Aeroacoustic Flow Source feature. This option includes neither viscous effects nor the effects of vibrating boundaries.
Smoothing
Select the Smoothing method as Isotropic diffusion (the default) or None. For the isotropic diffusion option, set the (numerical) Diffusion constant (the default: 1e-4). It is recommended to always use a small amount of smoothing to ensure smooth gradients of the background mean flow variables.