On some fundamental flaws in present aeroacoustic theory

A critical analysis of the main theoretical approaches to the theory of aerodynamic sound is presented for the case of inviscid gas flow. Various systems of acoustic equations are considered, with and without externally assigned source terms. Decomposition of flow variables into acoustic and non-acoustic components is discussed as a complex problem which is crucial for studying many aeroacoustic phenomena, and a new concept is suggested for this problem. A time-averaging procedure, which is usually applied for such a decomposition, is examined, and its essential flaws are revealed. The general formulation of Lighthill's acoustic analogy is analyzed as well as various subsequent approaches to the theory of sound generation. This analysis shows that in all these the definitions of aerodynamic sound sources are featured by evident defects, and so these models cannot be adopted as physically or mathematically accurate. The relevant problems of experimental and computational research are considered in connection with the theoretical models under discussion. (C) 2000 Academic Press.