Experimental investigation on the influence of liner non-uniformities on prevailing modes

From the in-flight measured circumferential modal spectra of the Rolls-Royce Tay 650 engine mounted on the Fokker 100, it was found that the sound field propagating upstream in the inlet is strongly modulated by intercostal hard-walled strips in the lined area, the non-cylindrical geometry of the duct, and the non-axisjnmnetric flow velocity...

Theory of sound propagation in a flow duct lined with annular segments of porous material

A theory is presented to calculate acoustic modes in a circular flow duct lined with porous material. The porous material is divided into annular segments by a rigid structure, which prevents axial sound propagation from one segment into the other. Single modes cannot exist in such a configuration, but it is shown that approximate solutions of...

Evaluation of the applicability of Helmholtz resonators for low frequency acoustic liners

A literature study has been carried out on the acoustic behaviour of those Helmholtz resonator type liners which are most promising for low frequency sound absorption in aero-engine applications. The equations for the acoustic impedance of various types of Helmholtz resonators have been analyzed as well as the conditions for the validity of...

Meetfouten bij intensiteitsmetingen, toegepast op de bepaling van geluidsisolatie

A study has been carried out on the errors, connected with acoustic intensity measurements, measuring the sound transmission loss of panels with the intensity method. The magnitude of some measuring errors can be estimated from available publications. From measurements in a standing wave tube and on a flat plate the measuring errors have been...

Experimental investigation of rotor/stator interaction noise generation, acoustic mode measurements

An experimental investigation was carried out in the low speed wind tunnel LST to study aircraft engine noise generation by rotor/stator interaction. Reported is a follow-up experiment including detailed acoustic measurements in the duct downstream of a rotor with cylindrical pins to complement earlier tests whereby rotor wake velocities and...

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...

Sensors for a system to control the liquid flow into an evaporative cold plate of a two-phase heat transport system for large spacecraft

Two-phase flow heat transport systems (thermal busses) for the Columbus Space Platform and the Space Station are expected to incorporate systems to control the liquid flow rates into the evaporative cold plates. Such a control system consists of a sensor that monitors the cold plate (performance), a control algorithm and an actuator i.e. a valve...

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 *)...

The NLR/NGTE joint programme on the measurement of attenuation and impedance in acoustic flow duct facilities.

The National Aerospace Laboratory NLR in the Netherlands and the National Gas Turbine Establishment NOTE operate similar acoustic flow duct facilities but with differences in their respective approaches to the measurement of attenuation and impedance of duct linings. A joint exercise was arranged with the object of comparing methods and results,...

Calculation of sound suppression in a circular three - sectioned uniform flow duct

It is concluded from this limited analytic study of pure tone sound suppression in a cylindrical duct with uniform flow, based on the mode matching technique, that the optimum of the liner impedance heavily depends on the source distribution and also on the length of the duct.

Calculation procedure for soimd propagation in a multisectional duct with uniform flow

A set of equations is presented for the sound propagation in an axisymmetric multisectional duct. For each side of a source section the combined duct effects of transmission, reflection and absorption are reduced to one matrix of coefficients. The procedure is compatible with a source description which takes the feedback of the sound field into...

On the sound field generated by a fan in a hard-walled baffled duct with uniform flow

The present status of a method to calculate the generation, transmission and radiation of fan noise is described. A steady uniform flow is assumed in the whole field. A hard-walled circular duct is considered which is terminated at the open end by an infinite baffle. The source mechanism is the impingement of wakes from an upstream blade row...

Een tweede serie orienterende geluidsvermoeiingsproeven op een triltafel

A second series of exploratory acoustic fatigue tests using a shaker. A second series of exploratory acoustic fatigue tests was carried out, again employing simple specimens mounted on a shaker. Strain measurements were compared with calculations. Crack growth initiated by a central notch was observed. A comparison was made between three types...

Sound transmission in and radiation from hard-walled annular ducts related to fan engine inlets

In this report the sound propagation in a hard-walled annular duct of finite length is investigated. The individual modal solutions so found are described. The main properties which are calculated in the present report, are the modal intensity and the modal far field directivity pattern. The modal intensity is determined by the rate of mode...

Calculation of acoustic modes in an infinite duct with shear flow and sound absorbing walls

The sound field in an infinitely long duct with shear flow and sound absorbing walls, but with the sound source unspecified, is analysed into its constituents, the acoustic duct modes. The equations, wave numbers, and various properties of the modes are discussed. Some calculated results are used to show the effects of shear flow and absorbing...

Noise environment in the NLR transonic windtunnel HST

Measurements of flow disturbances in the NLR - HST on the centerline and at the sidewall showed a maximiun noise level of 1 % in Cprms at a Mach number of 0.8. This is low compared with other ventilated wall tunnels of about the same size. Space-time correlations showed that a large part of the flow disturbances concisted of upstream travelling...