Not getting convergence using Explicit spatial and Transient formulation in Fluent.
 

I am trying to simulate the shock wave which is coming out from the shock tube from one of it's open(to ambient) end using the inviscid Model. For that I created a 3D Model and the enclosure is divided into several parts for proper meshing(Picture 1). Also attached some pictures with meshing(Pictures 2,3,4). Non reflective Pressure boundary conditions are applied at the surfaces of the ambient and the Pressure inlet at the other close end(Left end of driver side) of the shock tube.
So, I had tried with different courant Number starting from 1 with the first order and second order upwind but in both the case the y and z velocity is not converging. I attaching the graph below(Picture 5). This is generated with second order upwind and courant 1 and if I use first order upwind then those oscillation are minimized and gives a smooth graph but still the y and z velocity are not converging with explicit spatial and transient formulation and even residuals did not go below 10^ (-1).

Attachment 81889

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Can anyone tell me where I had done a mistake or what I have to do for convergence??

Some Missing Data
 

Here I am attaching the picture of the Pressure contours on the XY plane of the geometry.
Attachment 81895

Thank You.

Regards,
Prem.