Development and application of reduced reaction mechanisms for modeling high-speed reacting flows.

摘要

Advanced high-speed vehicles require propulsive devices which minimize losses associated with slowing of the air stream before combustion. To achieve this goal, a better understanding of the mixing and combustion of high-speed reacting flow fields is essential. CFD analysis provides a valuable tool to accomplish this task, in particular predicting the ignition and flame-holding characteristics of supersonic reacting flows. Because of the large number of reactive species involved and because of the large Reynolds and Damkohler numbers associated with these flows, the computational requirements in modeling such flows are enormous. Based on flow and chemical time scales, systematically developed reduced reaction mechanisms that retain the finite-rate effects of a detailed chemical kinetic mechanism are used here as a method of simplifying this effort, without loss of accuracy. For an oblique detonation wave, established by a supersonic flow of stoichiometric mixture of hydrogen and air past a wedge, three reduced-reaction mechanisms are developed by introducing steady-state approximations for the species OH, O and HO{dollar}sb2,{dollar} and implemented in a computer code that uses a MacCormack like scheme to integrate the governing equations. The induction length in the oblique detonation wave, along with the temperature and species profiles, predicted with the detailed and the reduced reaction mechanisms are used to measure the accuracy of the reduced reaction models developed. These models are also implemented in a static reactor model to test the ignition delay predictions under various conditions. Comparisons indicate a good agreement between the detailed solution and the reduced reaction mechanism solutions, indicating the validity of the approximations introduced. The static reactor model is also used to develop a reduced reaction mechanism for modeling the ignition phenomena of a mixture containing a "representative endothermic fuel" and air, to demonstrate the versatility of this approach. For this mixture, the ignition delay predictions obtained with the reduced reaction model are in excellent agreement with the predictions obtained with the detailed model.