Numerical study of finite-amplitude source reconstruction in one-dimension.

Abstract

Since its inception in the 1980s, near-field acoustic holography (NAH) has been widely used to determine structural source properties. More recently, it has also been used to determine aeroacoustic source behavior. Although several alternate forms of NAH have been developed, all are based on the (linear) Helmholtz equation and would presumably not function correctly for a finite-amplitude pressure wave propagating nonlinearly. However, when nonlinear effects or reconstruction distances are small, NAH may still be a useful tool for determining radiation characteristics of finite-amplitude sources such as jets and rockets. A one-dimensional numerical propagation scheme has been used to propagate broadband noise with various spectral shapes and amplitudes. A simple NAH-based magnitude reconstruction is used to determine frequency-, amplitude-, and propagation distance-dependent errors indicating in what regions linear NAH methods may produce large errors. The results indicate that the presence of shock coalescence causes relatively large errors in linear sound field reconstructions of broadband noise sources.