Vibroacoustics of Stiffened Structures in Mean Flow

Abstract

AbstractThis chapter is organized as two parts: in the first part, a theoretical modeling approach is proposed for noise radiated from aeroelastic skin plates of aircraft fuselage stiffened by orthogonally distributed rib-stiffeners and subjected to external jet noise in the presence of convected mean flow. The focus is placed upon quantifying the effects of external mean flow on the aeroelastic-acoustic characteristics of the rib-stiffened plate. The Euler-Bernoulli beam equation and the torsional wave equation governing separately the flexural and torsional motions of the rib-stiffeners are employed to accurately describe the force-moment coupling between the stiffeners and the plate. The external mean flow fluid is modeled using the convected wave equation. Given the periodicity of the considered structure, the resulting governing equations of the system are solved by applying the Poisson summation formula and the Fourier transformation technique. The radiated sound pressure is closely related to the plate displacement by means of the Helmholtz equation and the fluid-structure boundary conditions. To highlight the radiation characteristics of the periodically stiffened structure as well as the mean flow effects, the final radiated sound pressure is presented in the form of decibels with reference to that of a bare plate immersed in mean flow. Systematic parametric studies are conducted to evaluate the effects of external mean flow speed, noise incident angle, and periodic spacings on the aeroelastic-acoustic performance of the rib-stiffened plate.In the second part, this chapter investigates the sound transmission loss of aeroelastic plates reinforced by two sets of orthogonal rib-stiffeners in the presence of external mean flow. Built upon the periodicity of the structure, a comprehensive theoretical model is developed by considering the convection effect of mean flow. The rib-stiffeners are modeled by employing the Euler-Bernoulli beam theory and the torsional wave equation. While the solution for the transmission loss of the structure based on plate displacement and acoustic pressures is given in the form of space-harmonic series, the corresponding coefficients are obtained from the solution of a system of linear equations derived from the plate-beam coupling vibration governing equation and Helmholtz equation. The model predictions are validated by comparing with existing theoretical and experimental results in the absence of mean flow. A parametric study is subsequently performed to quantify the effects of mean flow as well as structure geometrical parameters upon the transmission loss. It is demonstrated that the transmission loss of periodically rib-stiffened structure is increased significantly with increasing Mach number of mean flow over a wide frequency range. The STL value for the case of sound wave incident downstream is pronouncedly larger than that associated with sound wave incident upstream.KeywordsExternal Mean FlowSound Transmission Loss (STL)Sound Power RadiationConvected Wave EquationBare PlateThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.