The Effects of Using Noise Reduction Turbofan Engine Nozzle Designs on a Turbojet Engine

Aircraft noise is a complex topic which is projected to increase with the increasing number of aircraft and size of the engines. Turbine-powered aircraft produce sounds that are considered pollutants at certain decibel levels. Turbofan engines are inherently quieter than turbojet engines for a given level of thrust. The purpose of this research is to determine if current turbofan noise reduction nozzles could reduce the amount of noise for turbojet engines at two different thrust levels. Three turbofan engine nozzles were designed and tested on a turbojet engine. Decibel levels of 30 frequencies for each of the nozzles were compared to the original turbojet nozzle using an indoor turbine power plant thrust cell. Six samples of thirty decibel levels and frequencies were recorded at idle and at a higher thrust level. Additional parameters of engine operation were also compared (oil pressure, oil temperature, exhaust gas temperature, thrust lever position, and fuel consumption). Results were evaluated in two ways: (1) the effect of each nozzle design in reducing noise by decibel level or frequency shift as compared to the original nozzle, and (2) change in the efficiency of the engine operation of each nozzle design as compared to the original nozzle. The turbofan nozzle designs did not result in any major improvements in reducing the overall noise levels. However, there were reductions of dB levels for some frequencies. Frequency shifts were apparent in all nozzle designs and most shifts were toward the higher frequencies.