The 2D and 3D turbulent airflow in channels with sharply bent walls is studied numerically. The inner surfaces of opposite walls are parallel to each other ahead of the bends and slightly divergent downstream. The inflow Mach number ranges from 1.2 to 1.5. Solutions of the Reynolds-averaged Navier-Stokes equations are obtained with a finite-volume solver on fine computational meshes. The solutions demonstrate flow hysteresis and bifurcations in considerable bands of the Mach number and angle of attack. The instability of shock waves is explained by their interaction with the expansion flow developed over the convex bend of a wall. Though the leading edges of walls are very thin, they produce noticeable effects on the flow.