Without directly solving either the Lighthill or FW-H equation to predict the sound pressure levels or power at some distance from the source, it is still useful to analyze the four types of sources (monopole, dipole, rotating dipole, and quadrupole). Analysis of the various source terms allows comparative evaluations of different designs, as well as comparison of the relative strengths of the various types of source terms. The main objectives of analysis of the various noise sources are:
Comparison of the relative noise source strengths for a given configuration. This type of comparison will enable you to determine which type of noise source dominates in your problem (monopole, dipole, or quadrupole). Once the dominant noise source is known, this reduces the cost of far field noise predictions because less overall data can be written.
Designs can be compared against one another to determine which produces less noise.
The maximum noise source level can be deduced by postprocessing the noise sources.
The noise source strengths can be written to files and used for input into any far field noise prediction software (for example, LMS Sysnoise or Virtual Lab Acoustics, or your own model).
There are various approaches for analysis of noise sources in CFX discussed in the following sections. Near field noise can be analyzed using CEL expressions and flow solver monitor points to create plots of sound pressure levels within the computational domain. While far field noise cannot be directly predicted, the common sources can be post processed and can also be written as transient solution fields from the flow solver on selected boundary conditions. You can control the data export using the Export Results tab on the Output Control dialog box in CFX-Pre. All files are written in a binary format called CGNS (http://www.cgns.org). The CGNS exported data is described in a later section.