Partial Chemical Equilibrium: Theory and Implementation in the Program Surf

Surf is a program for computing steady and inviscid, supersonic reacting flows in planar and axisymmetric nozzles. The program which was described in a previous report (Rein, 1989, named Surf report hereafter), has options for determining nonequilibrium, equilibrium and frozen flows, respectively. Further, the possibility of switching the computation from a fully equilibrium to a fully nonequilibrium flow calculation was introduced. This latter option aims at decreasing the CPU-time by reducing the stiffness inherent to the partial differential equation system used for modeling the flow. Exploring this concept more deeply, one eventually ends up with the idea of introducing partial equilibrium into Surf. The realization of this idea, both theoretically and practically, is subject of the present report.