Offset stream technology - comparison of results from UCI and GRC Experiments

Experime ntal results obtained in the UCI and GRC facilities, on noise reduction due to flow deflectors applied in the fan stream of a separate -flow nozzle , are compared. The nozzles involved in the former facility are geometrically similar but about 8 times smalle r than those in the latter . In general, there is good agreement in the effect of the deflectors observed in the two facilities. For a bypass ratio 8 nozzle, the changes in the noise spectral characteristics effected by two pairs of vanes are found to be es sentially identical. The overall noise attenuation (in terms of effective perceived noise level) is up to 0.4 EPNdB for this nozzle. For a lower bypass ratio nozzle, on the other hand, significant ly more attenuation is observed , however, the attenuation in the GRC facility (1.8 EPNdB) is not as pronounced as observed in the UCI facility (3.1 EPNdB) . Possible reasons for the dis crepancy are discussed.