ghost fluid method (GFM)
 

I want to solve shock tube problem by GFM. (according to Fedkew's paper). at initial time, there is not any shock wave. when does shock appear? because according to paper the shock speed is D=(ro1*u1^2+ro2*u2^2+p1-p2)/(ro1-ro2)?

when can I use this D for level set velocity (shock velocity)? (At what time step?)

Let me know if you have any experience with GFM in shock tube problem?