Interior noise field of a viscoelastic cylindrical shell excited by the TBL pressure fluctuations:Ⅰ. production mechanism of the noise

Applying the wavenumber frequency transfer function to describe the whole system including the elastic cylindrical shell and the fluid loading, a general expression of the cross spectrum of the interior noise induced by the TBL (Turbulent Boundary Layer) pressure fluctuations is derived. There are two production mechanisms of the noise: direct transfer of the convective ridge of the pressure fluctuations through the shell, and reradiation of resonance modes excited by pressure fluctuations. At low frequencies the noise produced by the latter mechanism is dominant. Solving the frequency equation of the cylindrical shell with liquid loading, the two Stoneley-type poles in the complex K plane are presented. They are major sources of the reradiation of shell at low frequencies. Finally, effects of the shell radius, shell thickness, material absorption and flow speeds on the noise reduction are computed by numerical integration.