Noise reduction in supersonic jets by nozzle fluidic inserts

This paper describes an innovative methodology and device for the reduction of supersonic jet noise. The goal is to develop a practical active noise reduction technique for low bypass ratio turbofan engines. This method introduces fluidic inserts installed in the divergent wall of a CD nozzle to replace hard-wall corrugation seals, which have been demonstrated to be effective by Seiner et al.¹. By altering the configuration and operating conditions of the fluidic inserts, active noise reduction for both mixing and shock noise has been obtained. Substantial noise reductions have been achieved for mixing noise in the maximum noise emission direction and in the forward arc for broadband shock associated noise. To achieve these reductions (on the order of 4 and 2 dB for the two main components respectively) practically achievable levels of injection mass flow rates have been used. The total injected mass flow rates were less than 4 % of the core mass flow rate and the effective operating injection pressure ratio was maintained at or below the same level as the nozzle pressure ratio of the core flow. Refinement and optimization of this technique is being pursued at Penn State University.