Abstract: Transonic wind tunnels play a crucial role in performance evaluation of flight vehicles, and the flow quality in the core test section directly affects the reliability of experimental measurements. Focusing on a 2.4-m transonic slotted-wall wind tunnel, this study employs a combination of Reynolds averaged Navier-Stokes (RANS) and large-eddy simulation (LES) methods to investigate the flow characteristics under high-subsonic conditions. Through iterative adjustments of boundary conditions of RANS cases, the coupled influences of wall slots, tunnel inlet and outlet conditions, and plenum suction on the core-flow field are clarified. To reproduce the upstream boundary-layer development, the equivalent turbulent boundary-layer approach is used to construct a compressible turbulent inflow consistent with the core-section inlet. LES indicate that the slotted walls effectively alleviate the boundary-layer displacement effect and reduce the streamwise rise of Mach number. The Kelvin-Helmholtz instability at the slot significantly affects the streamwise development of the boundary-layer thickness and the spatial distribution of the fluctuation intensity. This study provides a reliable modeling strategy and physical insight for numerical prediction of transonic wind-tunnel flows.