Question for B.C of 1-D piston problem

Yoo

Hello. Im trying to find out information on how to apply exit(outflow) boundary condition at end point to a one dimensional model i have constructed. In case of finite wave i can check good result but when i apply exit boundary condition at same position,that is open channel,the result is similar to solution of wall B.C. I expected the result that show the reflected expansion wave but still the reflected shock wave. Does this unsteady one dimensional problem need any other exit B.C?

Thanks in advance.