Acoustic measurements of co-annular jets at high subsonic-low supersonic jet velocities

This paper describes the results of experiments on a dual stream nearly co-annular high-speed jet. The experiments were conducted on a two-stream model whose design was provided by NASA Glenn Research Center with a Computer Aided Design file. This file was adapted to a smaller size in the ratio of 1:4.5 including connection fixtures to the existing air delivery system. A series of experiments was performed at several subsonic and supersonic conditions, with flow parameters that closely matched those used for experiments previously conducted at NASA Glenn. The data are presented first for two representative conditions in a progression from static conditions to “with simulated forward flight”, with the data presented as-measured with no corrections for the effect of the forward flight stream. The data are then corrected for the refraction and amplitude changes associated with the sound field as it crosses the shear layers that define the edges of the free jet, which represents the forward flight stream. The correction formulas used are those developed in the work of Amiet in 1975¹. In a final series of experiments, the far-field noise was compared directly to data provided by NASA Glenn from their previous experiments at the same operating conditions and nozzle geometry. This required the conversion of the NASA data to the same non-dimensional format as used for the Penn State data. Comparisons of the data for the static environment conditions produced excellent comparisons. There are occasional small spikes (or blips) in some of the data, perhaps caused by small resonances, but this did not appear to have a systematic effect on the data. The Penn State forward flight system is limited in its ability to produce forward flight Mach numbers in excess of M_f = 0.16, whereas the NASA data available had a flight speed of M_f = 0.24 or higher. Thus, the data for the forward flight conditions did not have the degree of agreement that was found in the static condition data but showed all the same trends. Additional test cases are available and are still being analyzed.