Hi all, Happy new year! I need a kind of zero gradient boundary condition (BC) for the compressible flow solver. As Neumann BC is not implemented for “LDGNS,” I tried using ExtrapOrder0 BC, but I got oscillations on this boundary. In my 2D simulation I have one Dirichlet and one ExtrapOrder0 BCs as the input and output of my domain and two Symmetry BCs on the top and bottom. The Mach number is very small (~0.001). Is this combination OK for the compressible flow solver? Do you suggest any other option instead of ExtrapOrder0 or Dirichlet BCs? Thanks in advance, Arash ----------------------------- Arash G. Nouri Research Scientist 1127 Benedum Hall Mechanical Engineering and Materials Science University of Pittsburgh E-mail: arash.nouri@pitt.edu