A Hybrid Method for Flows in Local Chemical Equilibrium and Nonequilibrium

The primary objective of this work is to develop a more e cient chemically active compressible Euler equation solver. Currently, a choice between the physical accuracy of a nite-rate solver or the computational e ciency of an equilibrium ow solver must be made. The number of species modeled continues to increase with available computational resources. A method of further leveraging the increase in computational power is desired. The hybrid chemistry scheme proposed here attempts to maintain the accuracy of niterate schemes while retaining some of the cost savings associated with equilibrium chemistry solvers. The method given uses a full nite-rate ux in regions where chemistry is slow compared to the advection rate and an equilibrium chemistry scheme in regions where the chemistry outpaces the uid transport. Control volume switching is based on a locally de ned Damk ohler number. This method could be extremely useful for full reaction path modeling or the tracking of a very large number of species. The cost of the solution algorithm is proportional to (NS + 4), where NS is the number of chemical species. Thus, eliminating the increased cost of solving for a large number of unknowns in regions where it is unjusti ed can be very useful. Tenasi, a University of Tennessee SimCenter research code, is used as a base for the new solver. The hybrid method is implemented and tested with an explicit solution technique in one dimension. In combination with a ve species air chemistry model, a high-temperature shock tube is used as a veri cation test case. Results are compared with those from pure equilibrium, full nite-rate, perfect gas Euler, and exact perfect gas Riemann solvers. Timings are also given as an indicator of the cost savings that would be possible should the hybrid method be extended using implicit algorithms.