Background
Sound emission occurs whenever a
fluid or other compressible media experiences a compression or rarefaction.
Common sources of sound are moving surfaces or diaphragms which act directly on the
media and also sheared fluid-flow, in which vortices create localized disturbances in
the pressure field. Acoustic disturbances audible to human ears can be generated
from tiny amounts of energy, yet are capable of propagating over large distances
with little attenuation. Simulating such phenomena with traditional time-dependent CFD
methods is usually impractical or impossible.
The CAA++ suite contains a range of products which incorporate a number of recent
advances in computational aeroacoustics technology. CAA++
enables users to tailor a cost-effective solution to
the problem of noise prediction. The simplest methods available require little
more effort than the calculation of a statistically-steady flow field - a
subject that is common practice in fluid dynamics through the use of Reynolds-averaged
Navier-Stokes equations with turbulence closures. Realizable turbulence closures
in CFD++ can be used to directly generate and export the necessary acoustics information (mean
flow and statistics) for CAA++.
Using the CAA++ tools, users can directly visualize noise-sources
or compute total output power metrics, in order to rapidly assess and compare one
design configuration with another. Analytic methods are available to simulate the
acoustic propagation from a set of modeled noise sources, enabling
a rapid prediction of full noise-spectra for a small number of
user-defined probes.
For problems involving near-field solid surfaces, sound blocking, refraction or reflection
from solid surfaces, including problems involving resonance, the CAA++ suite also
contains the NLAS acoustics solver, which uses perturbation equations to
numerically model the acoustic-wave transmission. The NLAS method provides
a general-purpose noise-prediction tool, able to account for both broadband,
fine-scale turbulence-related noise, as well as discrete tones
arising from coherent structures or resonance.