DAMPING OF SOUND AND VIBRATION BY FLOW NONLINEARITY IN THE APERTURES OF A PERFORATED ELASTIC SCREEN

An analysis is made of the influence of flow nonlinearity in the apert ures of a perforated elastic plate on the damping of sound and flexura l vibrations. Fluid is forced through the perforations by the pressure differential established across the plate by the incident disturbance . The Reynolds number is assumed to be sufficiently large that separat ion occurs, and the reciprocating aperture hows form 'jets' on alterna te sides of the plate. The growth of these jets is modelled by means o f a nonlinear equation proposed by Cummings (1986). This equation is s olved simultaneously with a generalized bending wave equation derived by the author (Howe, 1995a) which governs motions of a perforated elas tic plate whose lengths scales are large compared to the aperture spac ing. It is shown that significant attenuations of large amplitude acou stic waves can occur except when the frequency is so small that the pl ate is acoustically transparent. Bending waves are also damped provide d the amplitude of the plate surface velocity is not too large and the frequency is small enough to ensure the formation of substantial jets in the apertures. Numerical results are given for large amplitude sou nd waves incident on a perforated screen in air, and for bending waves propagating over aluminium and steel screens immersed in either air o r water.