On the effect of external flow on sound transmission into a thin cylindrical shell

Abstract

In the context of the transmission of airborne noise into an aircraft fuselage, a mathematical model is presented for the transmission of an oblique plane sound wave into a thin cylinder, including the effects of external air flow, internal pressurization, and different fluid properties outside and inside the cylinder. Numerical results are presented for different incidence angles at flow Mach numbers varying from M=0 to M=1.0 with acoustic properties taken at standard atmospheric conditions. It is shown that at M=0, the cylinder transmission loss has dips at fR (cylinder ring frequency) and fc (critical frequency for a flat panel of same material and thickness as shell). Below fR, cylinder resonances affect TL. Between fR and fc, cylinder TL follows a mass-law behavior. Flow provides a modest increase in TL in the mass-law region, and strongly interacts with the cylinder resonances below fR. At normal incidence, TL is unaffected by flow. Although internal pressure does affect cylinder modal resonances, its effect on sound transmission into the cylinder appears to be small. [Work supported by NASA Langley Research Center.]