As seen in this picture, an oblique shock was reflected off of a solid wall. I understand that the flow has to turn to continue the shock, but how does this work when it gets to a wall?
What happens to make the flow turn in the way that makes the reflected wave?
A shockwave is just a pressure wave. When it encounters the wall, part of the wave is reflected and part of it is refracted into the wall. The energy of the wave has to go somewhere, and if the atoms in the solid medium is not as willing to vibrate, the energy is redirected. Further, if the wave encounters a denser medium, the wave will also experience a $\pi$ phase-shift.
Another way to see it is that the medium and the surface of the solid oscillates due to the mechanical wave that is the shockwave. The surface must however also exhibit an equal and opposite reaction which represents the reflected wave. Part of it is "lost" into the solid.
The "physics" part of this wiki explains how the atoms in the medium of propagation behaves during the wave. This qustion also asked about pressure wave reflection with a detailed answer.
