大規模詳細反応機構を考慮した圧縮性燃焼流シミュレーションを可能とする高速・高効率な数値解析手法の開発とその評価

抄録

Assessment of a reacting flow solver with large detailed chemical kinetics is extensively performed in terms of its efficiency and capability. The present method solves the compressible Navier-Stokes equations with the chemical reaction source terms in the operator-splitting form, i.e., the chemical reaction and fluid parts are solved separately during one time step. For the chemical reaction, a dynamic multi-times scale (MTS) method is introduced for alleviating the stiffness. Several zero- to two-dimensional combustion problems with methane, n-butane, and n-heptane reaction mechanisms are used for the assessment of the present method. The ignition problems with the three reaction mechanisms demonstrate that the present method provides the higher efficiency with smaller time step size and larger number of chemical species, compared to a conventional implicit time integration method (VODE). The present method with MTS is 2∼30 times faster than the method with VODE for the ignition problems. The one-dimensional end-gas auto ignition problems with methane and n-butane reaction mechanisms also demonstrate the higher efficiency and the capability of the present method for capturing the interaction between combustion and compressibility, e.g., engine knocking-like behaviors. Further, the present assessment indicates that, if efficient time integration methods such as MTS were applied, the fluid part becomes the limiting factor for simulating reacting flows, because of the time-consuming calculation of the transport properties. The present problems show that the fluid part turns out to be more time-consuming than the chemical reaction part with more than 50 chemical species on the time step size of 1.e-8 s. As a result, the present method with MTS is 2∼5 times faster than the method with VODE for the one-dimensional problem. A detailed estimation of computational time for the transport properties is provided. Finally, the present method is successfully applied to the two-dimensional end-gas auto ignition phenomena of n-butane with available and reasonable computational resources.