Aeroacoustics

Aeroacoustics is the branch of acoustics that studies the generation, propagation, and control of sound produced by aerodynamic flows and the interaction of sound with moving fluids and structures. It covers physical mechanisms, measurement techniques, and methods to predict and reduce noise in engineering systems.

The field originated with the aerodynamic noise theory of Sir James Lighthill in 1952, which cast turbulent flow as an equivalent distribution of acoustic sources. Ffowcs Williams and Hawkings extended the theory in 1969 to account for solid boundaries, enabling practical predictions for aircraft, turbines, and other machinery. Today, computational aeroacoustics combines CFD with acoustic analogies, classical theories, and hybrid methods to predict far-field noise.

Major noise sources include turbulent boundary-layer noise, particularly at trailing edges; jet and plenum noise; rotorcraft and fan noise; ducted and open-channel flows; wind turbine blade noise; and flow-induced vibration. In compressible flows, shock-related noise can also contribute.

Methods often involve wind-tunnel experiments or in-field measurements using microphone arrays and beamforming, along with flow diagnostics such as particle image velocimetry. On the modeling side, direct numerical simulation and large-eddy simulation coupled with acoustic solvers (CFD-based or FW-H approaches) constitute computational aeroacoustics.

Applications span aerospace, automotive, wind energy, and building systems. The goal is to design quieter engines, airframes, HVAC equipment, and blades, while meeting environmental regulations and community noise concerns. Ongoing research focuses on improving predictive accuracy, developing active and passive noise control techniques, and enhancing computational efficiency.