  The work addresses 2D and 3D turbulent transonic flows past a wall with an
expansion corner. A curved shock wave is formed upstream of a cylinder located
above the corner. Numerical solutions of the Reynolds-averaged Navier-Stokes
equations are obtained on fine meshes with a finite-volume solver of the second
order accuracy. The solutions demonstrate the existence of adverse free-stream
Mach numbers which admit abrupt changes of the shock position at small
perturbations. This is explained by an instability of the closely spaced sonic
surface and shock wave on the wall.
