The aero-acoustic performance of a forward-slanted perforated tube attached to a convergent nozzle was evaluated experimentally. The sound pressure level and thrust of the tube were investigated and a good performance in noise suppression was found. Flow visualisation with the Schlieren system along with a high-speed video camera showed the disappearance of shock structure in the flow issued from the tube with forward-slanted perforations but not present in the flow from a solid tube without

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... perforations. The performance of the perforated tube with forward-slanted perforations was compared with that of different tubes 1) with backward-slanted perforations and 2) with perforations normal to the axis and 3) with a solid tube without any perforations. Among the tubes tested, the perforated tube with forward-slanted perforations showed the best performance. The tube suffered from minimum thrust loss compared with the backward-and the normally perforated tubes. The only a drawback of the tube with forward-slanted perforations was its generation of a tonal component at low pressure. The elimination of the inner sharp edge of the perforation or the reduction of tube thickness negated the drawback and improved the aero-acoustic performance of the tube with forward-slanted perforations.