A Combined Shape and Liner Optimization of a General Aeroengine Intake for Tone Noise Reduction

A novel acoustic design methodology for turbofan engine inlets is presented. A fan intake tonal noise propagation model is enhanced with its continuous adjoint formulation, having been first applied to design the intake. This is followed by the implement of a liner optimization study on the obtained optimal intake in which far-field noise attenuation due to the presence of a liner is maximized by adjusting the liner impedance. The dependence of optimal liner impedance on frequency is examined. The present paper aims at describing the potential of the combined shape optimization and liner optimization for low noise turbofan duct design. Prior to the optimization process, the implementation of the unsteady aeroacoustic adjoint method in shape optimization is validated by comparing the sensitivity derivative with that obtained by finite differences. The NASA flow impedance tube configuration is selected for benchmarking the time domain impedance condition (TDIBC) used in liner optimization. The examples presented demonstrate that significant noise reduction is achieved for most of the sound field by selecting the optimal shape and liner impedance. The result obtained confirms the effectiveness and efficiency of the proposed combined shape and liner optimization framework.