How is a wall boundary implemented (using ghost cells) in a simple 2d euler flow solver?

I understand that you must reflect the velocity of the cell across the wall and store that reflected velocity in the ghost cell (which will then be used for flux/residual calculations), but that is the extent of my understanding. I have tried implementing this in my euler flow solver but I am still seeming to get issues which makes me think there must be more to implementing a wall boundary condition.

• I guess a wall means here that there is no flow through this boundary. Then the BC must enforce zero flow velocity normal to the boundary. May 3 at 23:52

Maxim is correct that you need to enforce zero velocity normal to the wall in addition to the no slip condition. For the mass denisty equation, you could use $$\rho_{ghost} = \rho_0$$ where 0 is the index of the interior cell on the wall boundary.
$$T_{ghost}=2T_w -T_0$$