The role of castellations on pipe jet noise

This paper explores jet noise control using castellations at the exit of pipe-jets. Far-field acoustic measurements and schlieren visualizations are performed for two configurations of castellations; namely, two and four counts. The results are compared with that of pipe-jet without castellations. The nozzle pressure ratio range of the study is 1.5 to 4.5. With each configuration, the position and strength of vortices vary causing it to interact in different manners. For pipe with two castellations, the screech is amplified and the overall sound pressure level is higher than the reference jet in most of the nozzle pressure ratios under study. For pipe with four castellations, there is no noise variation in the azimuthal direction, and screech is eliminated at all nozzle pressure ratios.