Acoustic Simulation of Hot and Cold Flow mixing by a Lobed Mixer in a High Bypass Ratio Turbofan Engine

Noise reduction laws for turbofan engines require effective configurations to reduce the jet engine noise. Lobed mixers are known to be effective for noise-reduction in high-bypass-ratio turbofan engines. In this study, mixture of hot and cold flow is simulated in a lobed mixer for a high bypass ratio turbofan engine. Navier-Stokes equations are considered three-dimensional, compressible, steady and turbulent. To solve the turbulent flow, the k-ω SST turbulent model has been used; besides, to investigate the acoustic-power, Broadband noise source model was applied. In this research, first, the simulation method was validated and the results compared with the experimental data of previous studies. Then, the impact of the lobed mixer was investigated on mixing hot and cold flow and noise reduction in a high-bypass-ratio turbofan engine. The results of this study show that the maximum acoustic power was obtained about 72 dB at a distance of 14 meters from the nozzle, decreasing by moving away from the engine nozzle; also, the maximum amount of acoustic-power in the central-body at nozzle exit has decreased from about 90 dB to 72 dB. The maximum acoustic-power was observed about 95 dB on the mixer surface next to the central body flow. Finally, we can conclude that mixture of flow reduces the acoustic-power and improves its uniformity at the nozzle exit while increasing the acoustic-power near the central body.