Lately, due to the concentration of population in metropolitan areas, traffic congestion in the hub city has occurred, and future mobility AAM development is undergoing active progress to solve this situation. Accordingly, reducing noise pollution, which is pointed out as one of the problems of AAM, is an essential technical issue for urban operation. In this study, a duct, which is a representative aerodynamic noise reduction method, was used, and numerical analysis was performed using ANSYS FLUENT, a CFD software, according to the shape of struts in the duct. The FW-H of the transient-state LES model was used, and the steady-state analysis value was used as the initial value to save analysis time. Case 1 without strut, Case 2 with strut of an airfoil section, and Case 3 with strut of a rectangle section were designed and compared at a rotational speed of 6,000 RPM. Compared to Case 1, Case 2 and Case 3 showed improved thrust by about 7% and 2%, respectively. Compared to Case 2, Case 3 showed reduced OASPL from a minimum of 0.0793 dB to a maximum of 1.0072 dB. It was found that shapes of strut in the duct significantly affect thrust and aerodynamic noise.

Recently, as UAM has been in the spotlight worldwide, the issue of aerodynamic noise generated from propellers has emerged. Therefore, changes in thrust and aerodynamic noise were compared while changing the propeller lay-out distance. The designed propeller model was analyzed using ANSYS Fluent, a CFD software. Based on steady-state analysis, transient analysis was performed, and SPL was calculated using the FW-H noise model. Based on the standard propeller lay-out distance of 0.1 R (0.12 mm), 5 cases from 0.2 R to 0.6 R were compared with the reference model at equal intervals of 0.1 R. The thrust increased by up to 3.5% as the propeller distance increased. In most listeners positioned to measure SPL, noise was reduced by 0.07-0.7% in the improved model compared to the reference model due to reduction in local vorticity. However, because pressure fluctuation due to the increase in thrust and high SPL in the low-frequency region were measured, noise increased by 0.6% to 3.5% in some listeners. Increasing the propeller distance enhances thrust performance, but inevitably increases noise due to pressure fluctuations and SPL in the low-frequency region. Therefore, strict analysis of noise prediction according to a specific frequency and various design shapes are needed.

Recent use of mobile phones as a multimedia device has increased the development of micro-speaker modules having high quality and a compact size. Micro-speakers use polymer diaphragms fabricated by the thermoforming process. To improve the sound quality, micro-speaker diaphragms are usually designed to contain a number of micro-corrugations. This study investigated the effects of the corrugation depth on the acoustic characteristics of the diaphragm, using finite element (FE) analysis. Structural FE analysis was performed to investigate the stiffness change according to the corrugation depth. Modal FE analysis was used to compare the change in natural frequencies for each case. Harmonic response analysis further investigated the resulting variation in acoustic power. The effects of the corrugation depth on the acoustic characteristics of the diaphragm were discussed by reviewing all the FE analysis results synthetically.