Stability criteria for hybrid difference methods

The stability of hybrid difference methods, where different schemes are used in different parts of the domain, is examined for general schemes. It is shown that the energy method with the natural norm does not prove stability, but that the Kreiss or ‘GKS’ theory yields sufficient criteria for stability. While the analysis is general, it is discussed primarily in the context of hybrid schemes for shock/turbulence interactions, where a robust shock-capturing scheme is used around the discontinuities and an efficient linear scheme is used in other regions. An example of two coupled schemes that are individually stable yet unstable when coupled is given, showing that stability of hybrid methods is an important and non-trivial matter.