Acoustic damping of an annular tail-pipe under mean flow conditions
Wednesday 3 june, 2015, 11:20 - 11:40
0.3 Copenhagen (49)
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. 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 experiences 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 damping mechanism will be investigated qualitatively. The resulting slit resistance consists of a linear part depending on the air viscosity, and a non- linear part, the loss of kinetic energy of the fluidum through the slit. The presence of a laminar mean flow does not effect the acoustic performance of the annular tailpipe, only some minor effects are observed in the low frequency range. Even with a mean turbulent flow, the acoustic damping mechanism still remains intact.
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