A Zonal Euler/viscous Solver for Compressible Flows

We present a CFD zonal solver which efficiently simulates compressible viscous flows by reducing the computational cost through the use of a lower fidelity model, the Euler equations of inviscid flow, in regions where the flow is not dominated by viscous effects. This strategy also guarantees an acceptable level of accuracy. The design process can be accelerated if adequate solvers are used within each subdomain and a suitable method for passing information is used at the interface of these subdomains. In particular, the interface conditions play an extremely important role in ensuring continuity of the variables across the interface and they strongly affect the stability of the solver. Two implementations of the interface conditions are analysed: a strong approach where the variables are directly imposed on the interface and a weak approach based on a penalty method. The two methods are tested for the solution of the turbulent flow over a flat plate and a subsonic airfoil. Both approaches are able to perform a turbulent simulation saving 43% of the computational time respect to a complete turbulent simulation with an error of 10% in the wall friction coefficient.