抄録
Sound-reducing and a flow-accelerating effect due to the attachment of a porous tube to an underexpanded nozzle was experimentally investigated and the most suitable length of the porous tube as a noise suppressor was examined. In the present experiment, the porous tube had the same diameter as the standard nozzle to which it was attached and also the porous pattern was fixed. The measurement of mean flow and turbulence of the jets from the porous surface of the tube was carried out as well as the measurement of sound and exit Mach number. The ratio of the jet pressure ratio to the atmosphere was mainly 3 and 4.5. It was demonstrated by the present experiment that the flow at the exit of the porous tube changes from underexpansion to correct or over expansion by its elongation and that there exists a kind of optimal length to suppress the jet screech according to its pressure ratio.
