Improvement of Performance of a Perforated Tube as a Noise Suppressor by Oblique Perforation

The aeroacoustic performances of different perforated tubes were experimentally investigated. The length and the exit diameter of the tubes were fixed at 50mm and 10mm, respectively. Sound pressure level and thrust due to the exerted jet of the perforated tubes were measured and compared with each other. A perforated tube with forward-slanted perforations showed favorable performance. The shock structure of an underexpanded jet was removed using the perforated tube so that the generation of screech tone component was eliminated. However, the perforated tube with forward-slanted perforations suffered a discrete noise component when the jet pressure was very low. When the sharp edges at the inner surface of the perforated tube were removed the discrete component was eliminated. Moreover, the reduction in tube thickness also improved the noise suppression performance of the forward-slanted oblique perforated tube.