Abstract:

A computerized method for estimating near-field exhaust noise spectra from a database is provided. The variables considered in the interpolation/extrapolation routine make the procedure particularly applicable to estimating noise from a single-stream jet. The database 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 (e.g. combustion noise, shock noise, etc.). The method assumes that the jet is axisymmetric. The computation is carried out in two stages. First a least-squares fitting procedure is used to estimate noise spectra, for the required jet operating conditions, at each of the nine database locations closest to the location of interest. A second fitting procedure, based on spatial distance, is then used to obtain the noise spectrum at the location of interest. Appropriate weighting is included at each computational stage. Noise data are output as one-third octave band levels, and an option is also given to output spectrum values in dB/Hz or (N/m²)/Hz. The computer program includes routines for writing data to the database. To provide a basic prediction procedure for near-field jet noise, three databases are provided.