The acoustic Green's function for swirling flow in a lined duct

An Analytic Green’s Function for a Lined Circular Duct Containing Uniform Mean Flow (corr.)

An analytic Green’s function is derived for a lined circular duct, both hollow and annular, containing uniform mean flow, from first principles by Fourier transformation. The derived result takes the form of a common mode series. All modes are assumed to decay in their respective direction of propagation. A more comprehensive causality analysis suggests the possibility of upstream modes being r...

Sound Radiation from a Lined Exhaust Duct with Lined Afterbody

AFT fan noise radiating from the bypass exhaust duct is usually attenuated by acoustic lining along the inside of the duct only. The unconventional treatment of the afterbody, recently proposed by Tester et al. [1–3] has been shown to provide an additional potential of damping of the order of 1 to 4 dB. This is remarkable, given the fact that most of the sound is supposed to radiate away from, ...

A Difference Theory for Noise Propagation in an Acoustically Lined Duct with Mean Flow

Acoustic Instabilities on Swirling Flames

The POD makes possible to reduce the complete highdimensional acoustic field to a low-dimensional subspace where different modes are identified and let reconstruct in a simple way a high percentage of the variance of the field. Rotating modes are instabilities which are commonly observed in swirling flows. Such modes can appear under both cold and reacting conditions but that they have differen...

On acoustic instability phenomena in the vicinity of a lined wall exposed to a grazing flow

An experimental investigation of the acoustical behaviour of a liner in a rectangular channel with grazing flow has been conducted. The liner consists of a ceramic structure of parallel square channels: 1mm by 1 mm in cross section, 65 mm in length, and a surface density of 400 channels/inch square. The channels are rigidly terminated, thus constituting a locally reacting structure. In the abse...