Abstract:

ESDU 72002 gives a method of estimating the near field sound pressure levels due to high velocity jet noise from a single stationary conical nozzle. From a comparison with measured data, the accuracy of the estimated levels is expected to be within 5 dB, i.e. between approximately 60 per cent and 170 per cent of the actual r.m.s. pressure. Under reheat conditions, however, the discrepancy could be wider. At low jet velocities, where sources of noise other than pure jet mixing noise can be significant, the method underestimates the apparent jet noise. The noise levels predicted by the method described here are free field values but do not apply to the field within a conical surface emanating from the jet nozzle perimeter and expanding at a semi-angle of approximately 15 degrees relative to the jet axis, since this region contains the turbulent mixing region of the jet. The data are not applicable to the case of "shock cell noise", a phenomenon that can occur when a jet nozzle is operating in an over-choked condition. See also ESDU 99006 and ESDUpacs A9906, B9906 and C9906 for programs that provide a near-field noise database and a method of extrapolating outside it or interpolating within it.