Abstract: This article aims to provide technical support for designing the large closed-loop aeroacoustics wind tunnel with low turbulence intensity and low background noise at Beihang University (BHAW). The effects of the corner guide vanes angle on the flow fields are analyzed for several different expansion ratios by numerical simulations with the k-ω SST turbulence model, and the optimal installation angle of guide vanes for the BHAW wind tunnel is determined. Numerical results reveal that the pressure loss coefficient decreases first and then increases with the augmentation of the installation angle of guide vanes at each corner expansion ratio. The results further indicate the existence of a minimum pressure loss coefficient, and the installation angle of the guide vanes corresponding to the minimum value has a positive correlation with the corner expansion ratio. With various expansion ratios, the local pressure loss initially decreases and then increases with the guide vanes installation angle. The results demonstrate that the maximum friction loss coefficient occurs at the middle of the guide plate for a given installation angle; the installation angle mildly affects the flow around the central guide vanes (guide vanes 6, 7, and 8). With the increase of the corner expansion ratio, the flow velocity uniformity at the corner outlet deteriorates, and the installation angle of the guide vanes with the best flow guiding effect increases. By minimizing the total pressure loss coefficient and velocity deflection angle at the pipeline outlet, BHAW adopted an installation angle of 44° for the first corner with an expansion ratio of 1.17, an installation angle of 44° for the second corner with an expansion ratio of 1, an installation angle of 43° for the third corner with an expansion ratio of 1, and an installation angle of 42.5° for the fourth corner with an expansion ratio of 1. Such a strategy results in the dynamic pressure coefficient in the core area of the wind tunnel test section being less than 0.2% and the horizontal velocity deflection angle being less than 0.1°, justifying the aerodynamic design of BHAW.