Assessing impact of near-ground meteorology on spectral variability in static jet aircraft noise measurements Free

ANSI/ASA standard S12.75 (2012) provides guidance on allowable meteorological conditions for acoustical measurements of installed high-performance jet engines. This paper investigates meteorological effects on acquired acoustical data by analyzing recent measurements of a T-7A-installed GE F404 engine. During this measurement, the aircraft was run up six times at engine powers from idle to full afterburner, with test conditions following those prescribed by S12.75. However, far-field spectra are surprisingly variable, despite a morning measurement with low wind conditions. Analysis of the vertical temperature gradient shows a correlation between the gradient and spectral characteristics at distances as short as 38 m from the aircraft. The results suggest that local temperature profiles must be considered more carefully in future full-scale measurements and the results studied to establish guidelines for inclusion in the standard.