Caveat: I have no experience with OpenFOAM.

To visualize shock waves in general, you have a few options. The quick and dirty way is to just visualize contours of pressure. There will be a sharp, discontinuous pressure rise across the shock that should be readily apparent.

Slightly more sophisticated is numerical schlieren. OpenFOAM may have a fancy shadowgraph/schlieren capability. If not, you can get a similar effect using the absolute value of the density of gradient, and then plotting contours of that with a black to white color map. This is the formula I typically use:

NS = a * exp( -b * ( AGR - min(AGR) ) / ( max(AGR) - min(AGR) ) )

where:

AGR = abs( grad( rho ) )

a = a tunable constant, typically I use 0.8

b = a second tunable constant, typically I use 10 (don't forget the negative sign)

More sophisticated ray tracing techniques are possible for computational schlieren/shadowgraph, but, unless they are baked into OpenFOAM, they require a lot of coding to implement.

Hope this helps!

you will find many papers addressing the capability of OpenFOAM in solving shock problem (https://www.google.it/search?q=openfoam+shock+capturing&ie=utf-8&oe=utf-8&client=firefox-b&gfe_rd=cr&dcr=0&ei=mhVqWs29OufBXszmuugD)

I suggest also to check the OpenFOAM section of cfd-online-

I have succesfully used OpenFOAM's rhoCentralFoam for the simulation of a rocket engine plume. It is easy to use and accurate. For further information on OpenFOAM solvers for supersonic flow you can read this paper: http://www.cimec.org.ar/ojs/index.php/mc/article/viewFile/4231/4157