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.