Combined Flow Control Method for Supersonic Jet Noise Reduction

This paper outlines diagnostic experiments aimed at understanding and mitigating supersonic jet noise for the design Mach number of 1.6. Noise suppression is attempted by use of flow control devices like chevron, deflected seals, and a proposed combination of the deflected seal with chevron. The flowfield and acoustics are investigated at the design and at overexpanded pressure ratios (4.25, 2.75, and 3.25). Results have been derived by comparing the jet structure and jet acoustics of the different nozzles. Schlieren images indicate that the deflected seal chevron configuration (DS-CHN) nozzle diminishes shock strength while augmenting the jet perimeter in comparison to the baseline and other modified nozzles. A far-field acoustic study reveals that the suggested DS-CHN model greatly decreases screech noise for all tested pressure ratios. The recorded overall sound pressure level shows that the DS-CHN model achieved 1.5–2.5 dB reductions at all azimuths for pressure ratios of 2.75 and 3.25. Likewise, at a pressure ratio of 4.25, the proposed DS-CHN nozzle reduced 1 dB of overall sound pressure level across all tested polar angles. Additionally, the DS-CHN model gave better Mach number recovery at all tested pressure ratios.