Aeroacoustic Flow Source Coupling
The Aeroacoustic Flow Source Coupling () is a unidirectional multiphysics coupling between a Fluid Flow interface or imported CGNS data and the Aeroacoustic Flow Source feature in the Pressure Acoustics, Frequency Domain interface. The fluid flow model has to be set up either as a Large Eddy Simulations (LES), a Detached Eddy Simulation (DES), or a RANS-EVM model using the SST turbulence model with the scale-adaptive simulations (SAS) option. The data can also originate from The Imported Fluid Flow Interface interface and be based on imported CGNS flow data.
When coupled to a Fluid Flow 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.
When coupled to an Imported Fluid Flow interface (imported CGNS data), the physics interface sets up the dependent variables and the equations that are solved for in the Transient Mapping () study.
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. The coupling feature sets up the variables that are picked up by the Aeroacoustic Flow Source feature when finally, 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 (the flow source) 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. If the Aeroacoustic Flow Source is not selected in the full acoustics domain, make sure to select the interior boundaries to the acoustic domain, as they will contribute.
Coupled Interfaces
Select the Source and Destination physics. The source can only be a Fluid Flow physics interface with the LES, DES or RANS-EVM with SST-SAS as turbulence models, or it can be the Imported Fluid Flow physics interface. The destination is 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.
•
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.
•
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.
•
If the Imported Fluid Flow physics is selected as Source, only the Lighthill option exists and excess pressure as well as viscous stress effects cannot be included.
Smoothing
When coupled to a Fluid Flow interface, 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.