Аэроакустика: Ыңғайсыздау ағындардың шу тарататын қасиеттері

Aeroacoustics is a branch of acoustics that studies noise generation via either turbulent fluid motion or aerodynamic forces interacting with surfaces. Noise generation can also be associated with periodically varying flows. A notable example of this phenomenon is the Aeolian tones produced by wind blowing over fixed objects. Although no complete scientific theory of the generation of noise by aerodynamic flows has been established, most practical aeroacoustic analysis relies upon the so called aeroacoustic analogy, derive an aeroacoustic equation analogous to Lighthill's (i. e., an equation for sound generated by "turbulent" fluid motion), but for the incompressible flow of an inviscid fluid. The inhomogeneous wave equation that they obtain is for the pressure rather than for the density of the fluid. Furthermore, unlike Lighthill's equation, Landau and Lifshitz's equation is not exact; it is an approximation. If one is to allow for approximations to be made, a simpler way (without necessarily assuming the fluid is incompressible) to obtain an approximation to Lighthill's equation is to assume that , where and are the (characteristic) density and pressure of the fluid in its equilibrium state. Then, upon substitution the assumed relation between pressure and density into we obtain the equation (for an inviscid fluid, σ = 0)

And for the case when the fluid is indeed incompressible, i. e. (for some positive constant ) everywhere, then we obtain exactly the equation given in Landau and Lifshitz, and Hamilton and Morfey.