Resolvent-based framework for jet noise reduction of a low-bypass ratio coannular nozzle

The development of jet noise reduction (JNR) techniques is critical to the integration of supersonic aircraft into commercial travel and transportation. Prescribing JNR methods remains inherently difficult as the reduction of sound is frequently accompanied by a reduction in nozzle performance. This paper utilizes resolvent analysis as a reduced-order modeling technique for the purpose of assessing jet noise reduction concepts on a low bypass ratio coannular nozzle design. An automated framework is built to facilitate the computation of resolvent gain values for varying nozzle conditions and geometries. Specifically, parametric studies are conducted on the mixing duct length and extraction ratio parameters of the nozzle design. RANS mean flow data, used as input for the resolvent computation, are validated against experimental data for the same nozzle configuration. The resolvent analysis is verified by comparing sets of singular values and forcing/response modes against corresponding plots reported in the literature. Tailoring the resolvent framework with approaches using both near-field and far-field acoustics operators has been confirmed to reach consistent conclusions. Maximal gain profiles computed for a range of nozzle mixing duct lengths are found to be insensitive to this design parameter. Likewise, dominant gain profiles are also found to be insensitive to variations in extraction ratio at constant thrust. Both of these behaviors are found to be consistent with experimental data suggesting an insubstantial change in noise when varying these nozzle operating parameters. The findings of these parametric studies suggest that the maximal resolvent gain can be a viable proxy for jet noise. Applying resolvent analysis as a means to assess JNR potential shows promise for comparative design studies, though extending the study to more diverse nozzle conditions is necessary to affirm this.