Acoustic damping of an annular tail-pipe under mean flow conditions
Regular paper
KULeuven
Wednesday 3 june, 2015, 11:20 - 11:40
0.3 Copenhagen (49)
Abstract:
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.