Seto K., Khan M., Teramoto K., Kumamoto A., Kakinaga K.

The aeroacoustic performance of a forward-slanted perforated tube with different perforation patterns and different porosities has been experimentally investigated. We have already reported that a forward slanted perforated tube has a better performance of noise reduction of supersonic jets than the tubes of backward-slanted perforations and normal perforations to the tube axis. The only drawback of the tube with forward-slanted perforation was found to generate a tonal component at low pressure. However, that problem also has overcome partly by removing the sharpness of the inner surface of the perforations. Again to improve the efficiency of the forward slanted perforated tube in noise suppression, the perforation patterns (alternate and parallel) have been changed. Moreover, the numbers of perforation as well as the porosities of the forward slanted tubes were modified again to improve the performance of the tube and found the reasonable results. In the present report, we also compared the thrust loss of different types of forward slanted perforated tubes for various porosities and different perforation patters and identified a suitable type of forward slanted perforated tube which prevented the generation of peculiar tone at a wider range of pressure. All experiments were conducted inside an anechoic chamber. Acoustic data were taken by 8-channel data acquisition devises along with other apparatus and the jet structures were analyzed by Schlieren apparatus along with high-speed video camera. Thrust loss was measured through a vertical wind tunnel to receive the data directly. The performances of different types of slotted tubes were compared in the present experiment.