Analysis of the acoustic damping of an annular tail-pipe

A damping device, consisting of an annular tail-pipe, has been developed. It is applicable in situations wherein acoustic damping is required in combination with low flow resistance. Examples are ventilation systems, turbo-engines, intake and exhaust systems for internal combustion engines. The device consists of a central tube surrounded by a narrow slit. The central tube has an acoustic mass which impedance increases with frequency while the slit resistance remains constant. When the frequency has been increased sufficiently, a considerable part of the acoustic flow passes through the slit where it will be damped. In this way, acoustic energy can be dissipated while the flow experiances a low flow resistance. The acoustic properties of the device will be investigated using an electrical equivalent circuit. The impedance will be measured using an impedance measurement duct. The slit resistance will be identified and the damping mechanism will be investigated qualitatively. As result, the slit resistance consists of a linear part, which depends on the air viscosity, and a non-linear part, wherein the loss of kinetic energy of the moving fluidum through the slit causes acoustic damping.