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基于状态复用的燃烧反应动力学求解加速方法

A STATE REUSE RADAU FRAMEWORK FOR ACCELERATING COMBUSTION REACTION KINETICS

  • 摘要: 针对燃烧反应动力学刚性常微分方程求解中Jacobian构建和线性系统分解开销较高的问题, 在固定五阶Radau IIA方法基础上, 构建了一种基于状态复用的Radau加速求解方法(State Reuse Radau, SR-Radau), 旨在不改变原有离散格式和阶数性质的前提下降低计算开销. 该方法在简化Newton迭代过程中引入热化学状态相似性判断, 根据相邻接受步的热化学状态变化判断缓存Jacobian是否可继续使用, 并以接受步为单位更新和筛选缓存信息. 同时, 针对低浓度组分跨数量级变化和点火阶段强非线性特征, 进一步设计缓存质量检查、Jacobian重新计算、预运行诊断和回退处理机制, 用于限制低质量缓存被继续复用, 从而使缓存的Jacobian复用在状态相近且迭代表现稳定的区间, 并在高风险工况下转入更稳健的求解路线. 选取四种燃烧机理, 在1200 K、1400 K 和1600 K工况下进行验证, 代表变量包括温度、燃料、主要产物和关键自由基, 并采用代表变量轨迹误差和点火延迟误差评价积分精度. 结果表明, 除一个低温边界工况外, 该方法在11个满足误差约束的工况中均获得加速, 加速比为1.15 ~ 6.80; 并且该方法在保持主要物理量轨迹一致性的同时降低了构建Jacobian和分解线性系统的开销, 其预运行诊断机制可识别复用风险并在必要时切换至更稳健的求解方式.

     

    Abstract: To reduce the high cost of Jacobian construction and linear-system factorization in stiff ordinary differential equation integration for combustion reaction kinetics, a state-reuse accelerated solver, named State Reuse Radau (SR-Radau), was developed based on a fixed fifth-order Radau IIA method. The purpose of the method is to lower computational cost without changing the original discretization formula or order properties of Radau IIA. In the simplified Newton iteration, thermochemical-state similarity is introduced to judge whether a cached Jacobian can still be used. The decision is based on variations in thermochemical state between adjacent accepted steps, and the cache information is updated and screened along the accepted-step sequence. For low-concentration species with variations across several orders of magnitude and for strongly nonlinear ignition stages, cache-quality checks, Jacobian recomputation, pre-integration diagnosis, and fallback treatment are further designed. These treatments are used to restrict the continued reuse of low-quality cached Jacobians, so that cached Jacobians are mainly reused in intervals where the thermochemical states are close and the Newton iteration remains stable. When the pre-integration diagnosis indicates a high reuse risk, the computation is switched to a more robust integration route. Four combustion mechanisms covering different fuel types and mechanism sizes were tested at 1200 K, 1400 K, and 1600 K under the same constant-pressure adiabatic zero-dimensional ignition model to evaluate the proposed method. The representative variables include temperature, fuel, major products, and key radicals, and numerical accuracy is assessed using trajectory and ignition-delay errors. The results show that, except for one low-temperature boundary case, SR-Radau achieves acceleration in 11 cases satisfying the error constraints, with speedups from 1.15 to 6.80. Representative-variable trajectories, error metrics, and computational-cost indicators, including function evaluations, Jacobian evaluations, and lower-upper (LU) factorizations recorded during the solver runs, show that the method reduces the cost of Jacobian construction and linear-system factorization while maintaining the consistency of the main physical trajectories. The pre-integration diagnosis can identify reuse risks and switch to a more robust solver when necessary.

     

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