Understanding Wind Noise
Aeroacoustic (airflow-induced) noise is a difficult topic, and its theory is still under development.
Understanding aeroacoustic noise requires accounting for the physics of both unsteady flow and sound waves simultaneously. Although no complete scientific theory of the generation of noise by aeroacoustic flows has been established, most practical analysis relies on the so-called 'aeroacoustic analogy'*, proposed by Sir James Lighthill.
Simply stated, a vortical field (turbulent wind) impinging on a solid body (outer ear) can create unsteady surface pressure fluctuations. These surface pressure fluctuations can produce weak acoustic sound waves (wind noise). The shape of the outer ear adds considerable complexity to these surface pressure fluctuations and sound waves.
Measuring aeroacoustic noise with both external and in-canal microphones.
Measuring source region aeroacoustic noise at different locations and velocities.
Measuring turbulent pressure fluctuations and correlating to in ear wind noise measurements.
Smoke flow visualization / laser light imagery and fluorescein dye visualization / laser light imagery.
Constructive testing and analysis. Adding and subtracting different parts of the ear using modeling clay.
Hot wire and static / dynamic pressure probe anemometers. Measuring and mapping flow / velocity patterns.
* "Lighthill's theory of aerodynamic noise consists in drawing an analogy between the full nonlinear flow problem and the linear theory of classical acoustics." - Principles of Aerodynamic Noise Generation, D. G. Crighton, Department of Applied Mathematical Studies, University of Leeds, Leeds, England (1975)
Understanding wind noise helps us develop the most effective products.