MUSCL Differencing Scheme
I'm writing code to do MUSCL differencing on a structured grid. I'm modeling supersonic flow through an irregularly shaped duct.
I understand how to do the interpolation to get the state vectors at the cell faces for the internal points, but it isn't clear to me what the best approach is to calculate the value of the state vectors at the cell faces for the cells on the boundary of the computational domain since the interpolations extend outside of the defined grid. I have constant flow into and out of the computational domain, so I assume I can just use the inlet values for the cells at i=1 and the outlet values for the cells at i=imax+1. Where I run into issues is for the cell faces on the nodes that border the walls. Do I assume values for j=1 and j=jmax are equal to 0 since there is no flow outside of the computational domain, assume those locations have the same values as that seen at the wall, or make some other assumption? Any advice would be appreciated. Thanks, Robert 
Most people use ghost cells  the grid is extended and values are loaded into the cells outside the flow domain using extrapolation consistent with the boundary conditions. These values then allow a full width MUSCL extrapolation to be performed. The ghost cells are usually constructed based on some reflection of the geometry (i.e. grid points) across the boundary surface.

agd, thanks for the reply. I had to do a bit of reading on how to best set up the ghost cells, but I think I have it now.

MUSCL for irregular structured mesh
Hi RSeeley
i simulated several test case such as double mach reflection, mach 3 forward facing step flow in pure rectangular grid with MUSCL scheme, but i am very confused about irregular structured mesh in FVM approach with MUSCL scheme. can u help me to calculate Flux in 4 interface of cell? Thanks with best regards 
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