Noise is becoming generally accepted as an environmental and even health hazard to the population. Many noise sources are man-made – especially transportation noise from road traffic, aircraft, and trains. Other technical noise sources can also be annoying such as wind turbines or cooling and climate systems. Governmental reactions to noise problems and loss of public acceptance are laws, regulations, decrees, and guidelines for the certification of noise-emitting vehicles and machines as well as temporal or spatial limitations of their use. Aircraft and jet engine manufacturers in particular face increasingly stringent noise requirements for near-airport operations worldwide.

Aerodynamic noise is one of the major contributors to external vehicle noise emission. It also contributes to internal vehicle noise owing to the transmission of the externally generated noise through structure and window surfaces into the cabin. Aerodynamic noise becomes dominant at driving speeds exceeding 100 km/h when compared with structure-borne, power train, and tire noise for which substantial noise reduction has been achieved. The interaction of the flow with the geometrical singularities of the vehicle body produces unsteady turbulent flows, often detached, resulting in an increased aerodynamic noise radiation.

To achieve these noise reductions, the European Commission, for example, has laid out a series of research objectives. In order to meet the challenging goals proclaimed, the design process needs to be supported by computer-based noise prediction tools.

Governing equations and acoustic analogies

In principle, the way to predict aerodynamic noise generation and propagation is straightforward.