In the present study, experiments were conducted to investigate the interaction of supersonic underexpanded jet delivered from a convergent nozzle with a coannular tube on both the flowfield and noise emission. The effects of varying the tube length,
L, and diameter,
D, were investigated. The most pronounced noise reduction was observed at
D/
Dj = 2.2 at a jet nozzle pressure ratio (NPR) of 5, where the noise emission was reduced by approximately 30 dB compared with the baseline jet. Considerable sound pressure level (SPL) reduction over the measured frequency range was observed and the screech tone was completely suppressed. The schlieren photographs revealed that the shock-cell structure of the baseline jet disappeared at
D/
Dj = 1.9 as well as for higher values of
D/
Dj outside the tube. Detailed experimental investigations were carried out to explain the reduction in the noise radiated at
D/
Dj = 2.2. From these results, it was made clear that the Mach disk for the case of
D/
Dj = 2.2 extends up to the tube inner surface and the entire flowfield downstream of the Mach disk becomes subsonic. This was not observed for other cases of
D/
Dj where the time average flowfield is characterized by a repeated shock-cell structure inside or outside the tube. The effect of varying the jet nozzle pressure ratio (NPR), tube clearance and tube wall porosity on noise emission, flowfield and the associated thrust loss are reported.
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