Nonlinear partial differential equations modeling turbulentv fluid flow and similar processes present special challanges in numerical analysis. Regions of stability of implicit-explicit
methods are reviewed, and an energy norm based on Dahlquist's concept of G-stability is developed.
Using this norm, a time-stepping Crank-Nicolson Adams-Bashforth 2 implicit-explicit
method for solving spatially-discretized convection-diffusion equations of this type is analyzed and
shown to be unconditionally stable.