ESDU Engineer

Computer-based estimation procedure for single-stream jetnoise

The problems associated with the estimation of noise levels from jet engines are of particular concern to operators of jet-powered aircraft. There is a need to predict jet noise levels at many jet operating conditions.

Data Item 98019 provides a computerised method for estimating exhaust noise spectra from a given database. The variables considered in the interpolation/extrapolation routine on which this method is based make the procedure particularly applicable to estimating noise from a single-stream jet.

The major advantage of this method over earlier graphical approaches is the ease with which the database may be altered. This means that new data can be used as they become available without modification to the computing procedure. The database used need not be restricted to data for an isolated single-stream jet but could include installation effects as well as other components of single-stream engine noise. The computation involves a least-squares surface fitting procedure that may be of bi-linear or bi-quadratic form. Appropriate weighting of the data is included.

To provide a basic prediction procedure for the estimation of far-field, jet mixing noise from static jet engines with circular nozzles, a comprehensive database is provided. The computer program may be used with the provided database or a database generated from the user’s data. A computer program to generate a database from the user’s data is also provided.