W/D S/S BY ESDU 01004, ESDU 11002

INTRODUCTION

This Item provides a computerised method for estimating exhaust noise spectra in one-third octave bands from a given database. The procedure is an interpolation/extrapolation routine which, because of the variables considered, is particularly applicable to estimating the noise from a coaxial jet. Because the procedure is essentially one of interpolation of noise spectra, the particular form of the database need not be restricted to data for an isolated coaxial jet, but could be of a more complex nature (such as a database obtained from an engine including combustion noise, shock noise, flight and installation effects and from alternative engine geometries). In order to be able to illustrate the use of the method, an example database is provided for the case of far-field, coaxial, subsonic jet mixing noise from stationary, coplanar conical nozzles. The noise estimation method has been validated for use with a provided database and also with another database using a different third independent variable.

An advantage of this method over other approaches is the ease with which the database may be altered: new data can be added as they become available without modification to the computing procedure.

A simple introduction to jet mixing noise, together with other types of gas turbine exhaust noise, is given in Item No. 74001 (Reference 3). A computer-based estimation procedure for single-stream jet noise including a database for far-field jet mixing noise from circular nozzles for a stationary source is given in Item No. 85018 (Reference 5).

Two different computer programs are provided, one in FORTRAN 77 programming language and the other in Microsoft BASIC. Using three independent variables, a minimum of ten points is required in the database.