Numerical Simulations of Noise Reduction Devices for Aero Engines

Increasing air traffic and denser population around airports have led to stricterregulations on aircraft noise. The engine is the main source of noise of jet aircraft.Decreasing jet engine noise can in some cases reduce sonic fatigue andthereby increase the engine lifetime. In this thesis the performance of a novellow-frequency acoustic liner concept is investigated using unsteady Reynolds-Averaged Navier-Stokes simulations (URANS). The results are compared withthose of an analytical model and experiments. The liner is designed to reduce fannoise upon placement on the outlet guide vanes. Furthermore, the response of theradiated noise from a supersonic jet emitted from a converging diverging nozzleto steady-state and pulsed fluidic injection is tested using Large Eddy Simulation(LES). An investigation is also presented in which actions were taken to reducethe internal shock strength by modifying the nozzle throat, and thereby reduce theresulting noise. The optimized nozzle was evaluated further using LES and experimentaltechniques. The acoustic liner study showed that the resonance frequencyof the liner obtained by the URANS compared within 200Hz to the measuredresonance frequency. It was shown that the analytical model can be tuned with asingle parameter to match the URANS simulations over a wide range of frequencies.Simulations of the sharp throat CD-nozzle with and without fluidic injectioncompared within 2 dB to the measured values of the overall sound pressure level(OASPL) for all observers. The pulsed injection showed that the radiated noiseis sensitive to the pulsation characteristics and the frequency. It was shown thatnoise reduction with pulsed injection can equal the noise reduction of steady-stateinjection with lower net mass flow of the pulsed injection. However, an increasednoise was noted at the downstream observers. The optimized nozzle nearly eliminatesthe internal shock, which reduces the double diamond structure in the jetplume but increases the strength of the shock at the nozzle exit. It has lower turbulencelevels at the nozzle exit due to a weaker shock interaction with the shearlayer. The optimized nozzle provides equal thrust to the sharp nozzle with 4%lesspressure without any acoustic penalty. Good comparison is obtained with RANS,LES and experiments