To study sound propagation of aerodynamically generated noise, Mechanical enables you to import an Aeroacoustic Source loading condition into either a Coupled Field Harmonics or Harmonic Acoustics analysis system. You create this loading condition in Ansys® Fluent®, and then import it into a supported downstream Mechanical system, to solve for sound propagation.
Go to a section topic:
Assumptions
Note the following:
You must assign the appropriate acoustics material to the bodies of model.
You are required to create the required source file.
This feature is only applicable for low Mach number flows.
There may be modelling errors due to the Lighthill aeroacoustics analogy of splitting the compressible flow variables into the two parts (flow and acoustics) and handling them separately with the two approximate mathematical models connection through a source term in the wave equation.
Activate Beta Options and Feature Flag
This procedure requires you to close the application in order to make the feature available.
Activate Beta Options. You need to select and then close the dialog for the next option to become available.
To activate the feature selection option highlighted below, select the Tools drop-down menu, and then Options. This displays the dialog shown below. Select the Mechanical option from the tree. Scroll to the Linear Dynamics group and select Aeroacoustic Source Load.
As prompted, close and reopen the Ansys® Workbench™ application.
Application
This procedure uses a Harmonic Acoustics analysis to illustrated the steps to import an Aeroacoustic Source loading condition.
Right-click the Environment object in the Outline and select Insert > Imported Load > Fluids Results (Beta).
Using the Result File property, navigate to and select your *.dat.h5 file created Fluent. The *.cas.h5 file must also be available in the same folder as the *.dat.h5.
Right-click the Imported Load (Fluids Results File (Beta)) object and select Aeroacoustic Source (Beta).
Select the desired acoustic bodies (only) using the Geometry property and click Apply.
Right-click the Aeroacoustic Source (Beta) object and select Import Load.
Complete any additional property specifications. Note that:
You apply this load using the using the data processing framework (DPF) to generate a binary file: the Mapped Data property set to To Binary File. See the Load Mapping Workflow Specification section for the steps to complete any required specifications.
This feature supports source frequency filtering and source frequency interpolation.
You can specify one or more CFD domains/zones using the CFD Domain property.
The divergence of the Lighthill tensor (a vector quantity) is transferred from the CFD cell center to the acoustic finite element node using the Point Cloud algorithm. Therefore, only the Triangulation and Distance Based Average mapping is supported.
Source Term Computation in Ansys Fluent
Aerodynamically generated noise for low Mach number flows can be predicted using the Lighthill’s analogy. This offers an efficient alternative for the direct method which is computationally expensive. Lighthill developed the following wave equation using the continuity and momentum equations of motions:
Where the Lighthill Tensor (
) is:
And the variables are:
 = Fluid density. |
 = Flow velocity. |
 = Destiny at rest. |
 = Speed of sound at rest. |
 = Lighthill tensor. |
 = Reynolds stress tensor. |
For low Mach number, incompressible flow, the Lighthill Tensor can be approximated as only the Reynolds stress term:
The divergence of this Lighthill Tensor also known as Aeroacoustic Source can be applied as the sound source term to solve for the sound propagation in Harmonic Acoustic wave equation in Mechanical. The divergence of this Lighthill Tensor can be obtained using the named expressions in Fluent. Then, a Discrete Fourier Transform is performed to transform the results in the frequency domain. These transformed results can be written to a Case and Data (extensions?) file that can be imported in to Mechanical.
See the following sections of the Fluent User’s Guide for more information: