科研之友
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摘要
The aeroacoustic performance of three noise reduction ideas for fighter aircraft has been evaluated in one-fifth model scale testing, in stand-alone mode, and in combinations thereof in the Low Speed Aeroacoustic Facility at The Boeing Company. These three concepts consist of microjet injections of air and water, corrugated nozzle inserts, and beveled nozzles. Several bevel angles of 20, 24,28 and 35 degrees at typical military takeoff power, and 24 and 32 degrees at reduced power, were considered with two representative geometric models. The static thrust performance of all the modified nozzles is superior or comparable to that of the baseline nozzle. The model scale noise measurements have been extrapolated to full-scale conditions. The salient results of the acoustic performance at typical military takeoff power, assessed over a range of freestream Mach numbers from 0.0 to 0.32, are as follows. First, the water injection produces a larger benefit at the lower polar angles (measured from the nozzle inlet axis) where the shock component is dominant; the magnitude of the benefit in the dBA metric varies from similar to 2 to similar to 3 bBA at a polar angle of 60 degrees and drops to similar to 1 d BA at 90 degrees. The benefit at large aft angles is d BA. Second, the corrugations provide the largest benefit at the lower polar angles. The d BA benefit is similar to 4 d BA for a range of freestream Mach numbers from 0.16 to 0.32. As for the water injection, the benefit drops to similar to 1 d BA at 90 degrees. At the aft angles, there is a benefit of similar to 3 to similar to 3.5 d BA. Third, the beveled nozzles provide little modifications to the spectra at the lower polar angles. All of them provide a benefit in the dBA metric in the peak radiation sector: the magnitude of the benefit increases with the bevel angle and reaches a value of similar to 4 d BA for bevel 35. Fourth, the addition of water in conjunction with the corrugations and the bevels augments the noise benefit similar to 1 d BA at the lower angles and reduces the benefit in the aft angles. Fifth, all the concepts provide a benefit in the effective perceived noise level metric. At the reduced cutback power, the magnitude of the noise benefit is larger in the forward quadrant. The reasons for the observed noise reduction are examined for the different nozzle configurations.
- 出版日期2011-4
