An acoustic source modeling technique to predict the near sound field of axisymmetric turbulent jets

A procedure which allows the prediction of the near sound field of a circular jet by modeling the sound sources in the jet is developed. Far field, one-third octave sound pressure level data at various angles to the jet axis were obtained for an axisymmetric subsonic turbulent jet. The parameters varied were the jet exit velocities and stagnation temperature of the flow. The near field acoustic data at different radial locations and for the same test conditions were obtained. The strengths of the various source components at a particular frequency were determined by a constrained least-squares fit to the far field directivity pattern. The effects of sound source motion and distribution of the sources with frequency were taken into consideration and the near field sound pressure levels were predicted from the far field acoustic data. The experimental data for the near field and the predictions agreed fairly well.

The effect of Doppler shift in the observed frequency for a particular source frequency was studied. The Doppler shift correction was applied to the observed frequencies and the theoretical analysis was again carried out. This correction, however, did not indicate an improvement in the predicted results over that obtained before applying the correction.