Soundwaves around a transonic airfoil

B

Hi Guys, A while back I saw a diagram in a textbook (sadly I can't remember its name) that showed the propagation of sound waves around a transonic airfoil. The point of the diagram was to illustrate the development of the shock wave (by the piling-up of pressure disturbances) as being caused by the different domain of dependence in subsonic and supersonic flow.

Does anyone know of a good source of this (or similar) diagram? I'm looking for something that can explain the origin of a normal shock in terms of the sound waves generated in the subsonic and supersonic portions of the flow. I have tried to draw one myself using illustrator but can't seem to get it quite right.

If someone could point me in the right direction I'd be very grateful. B