The acoustics of a lined duct with flow

The present report describes a theory to calculate the sound propagation (including attenuation, reflection, radiation) through a three-sectioned cylindrical flow duct, modelling an aero-engine inlet. The flow is uniform apart from a thin boundary layer; two of the three sections are hardwalled, with an impedance-walled section in between. The...

Ongewone modes in een kanaal met impedantiewand

This paper describes and explains the appearance of certain acoustic modes of irregular behaviour in a duct with an impedance wall. Considered are the cases with and without a uniform mean flow. For high frequencies these modes become surface waves, exponentially confined to the wall region. The various regions of existence in impedance- and...

Voorstel tot modernisering kanaalakoestisch model voor de berekening van geluidvoortplanting in motorinlaten

Hydrodynamic instabilities and surface waves in a flow over an impedance wall

A 2-D analysis is made of the surface waves in a subsonic compressible uniform mean flow along an impedance wall. It is found that a maximum of four surface waves is possible. The regions of existence in complex impedance and wave number planes are given. One wave is found to travel upstream, while the others, one of which is an instability,...

Note on the Kutta condition in Glauert's series solution of the thin airfoil problem

In this note the classical Glauert's series solution of the thin airfoil problem is reconsidered. Glauert's solution involves a transformation of the independent variable, and a Fourier sine-series expansion. It is shown that, in contrast to what is frequently stated, the sine-series does not imply the Kutta condition. The Kutta condition is...

A study on the transmission of sound through flow ducts of varying cross section

A study is made of sound propagation through axially varying ducts with mean flow. Several analytical and numerical approaches are considered, and discussed with respect to their possibilities and limitations. Two new analytical theories, relevant for low and for high frequencies, are worked out in some detail. A fortuitously available *)...

Contributions to the theory of sound propagation in ducts with bulk-reacting lining

A theoretical analysis is presented of sound propagation in cylindrical ducts lined with porous material (bulk absorbers). Various configurations are discussed: (i) The porous material is homogeneous; then the sound field is built up of modes, (ii) The properties of the liner vary slowly in axial direction. A pure modal solution is in general...

Analysis of the near and far field of sound generated by propellers with or without the presence of a fuselage

A formal description is given of the sound field of a propeller due to surface pressure and blade displacement effects. The starting point of the analysis is the Ffowcs Williams and Hawkings equation, with the Lighthill stress tensor neglected. After (1) the introduction, (2) a general formula is given to describe the frequency components of the...

Acoustic radiation from a semi-infinite annular duct in a uniform subsonic mean flow

Using a Wiener-Hopf approach, ain analytical description is derived of the scattered field of a harmonic sound wave coming out of an open ended annular duct (a semi-infinite cylinder inside of which, coaxially, a doubly infinite hub), submerged in a subsonic, coaxial, uniform mean flow. The possibility of vortex shedding from the pipe exit edge...

On the acoustical implications of vortex shedding from an exhaust pipe

Asymptotic approximations for small Strouhal number are derived for the solution of the problem of the interaction between an acoustic wave and a subsonic jet flow issuing from a semi-infinite pipe. Density and sound speed differences between the jet flow and the (slowly moving) ambient medium, and a general edge condition are included. The...

A small strouhal number analysis for acoustic wave - jet flow - pipe interaction

Asymptotic expansions for small Strouhal number, valid for arbitrary subsonic Mach number, are derived for the solution of a simple problem of the interaction between an acoustic wave, a jet flow and a pipe, based on Munt's (1977) exact formal solution. These expansions relate to the pressure and velocity fluctuations in the jet flow and in the...

Sound diffraction at a trailing edge

The diffraction of externally generated sound in a uniformly moving flow at the trailing edge of a flat plate is studied, with some emphasis on the role of the Kutta condition. The pulse from a line source, a plane incident pulse and a plane harmonic incident wave are considered. The harmonic case is extended to include viscosity, using results...