Positivity-preserving CE/SE schemes for solving the compressible Euler and Navier-Stokes equations on hybrid unstructured meshes

We construct positivity-preserving space-time conservation element and solution element (CE/SE) schemes for solving the compressible Euler and Navier-Stokes equations on hybrid unstructured meshes consisting of triangular and rectangular elements. The schemes use an a posteriori limiter to prevent negative densities and pressures based on the premise of preserving optimal accuracy. The limiter enforces a constraint for spatial derivatives and does not change the conservative property of CE/SE schemes. Several numerical examples suggest that the proposed schemes preserve accuracy for smooth flows and strictly preserve positivity of densities and pressures for the problems involving near vacuum and very strong discontinuities.