Abstract
The acoustical characteristics of the noise radiated from combined jets exhausted from one main nozzle and 1, 2, 4, or 8 subnozzles which were placed asymmetrically or symmetrically to the main nozzle were investigated experimentally. The diameter d of the main nozzle was 5 mm and that of subnozzle a/d was 0.2 or 0.6, where a is the diameter of the subnozzle. The center-to-center spacing b of the main and subnozzles was fixed to 5 mm (b/d=1.0). In this experiment, the pressure ratio R of the jets was varied from 2.00 to 6.33. From the frequency characteristics of the screech tone, it is found that in almost all cases, two oscillation modes appear, but when eight subjets with a/d=0.6 were used, the screech tone disappeared completely. Although the total cross-sectional area of the multiple nozzles was larger than that of a single jet, it is found that the sound-pressure level radiated from multijets becomes the same or lower than that from the single jet. [Work supported by the Ministry of Education and Culture of Japan, Grant No. C2-09650187.]
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