Instability of the shock wave/ sonic surface interaction

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.