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Extension of the turbulent flame speed closure model to ignition in multiphase flows

机译：将湍流火焰速度闭合模型扩展到多相流中的点火

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摘要

An extension of the turbulent flame speed closure model rendering the model applicable to multiphase flow and ignition is presented. As formerly no coupling between reaction progress variable and enthalpy was existent, except through the temperature dependency of the laminar flame speed, an adaptation is proposed which offers an interface to initiate the combustion process. The modification to incorporate multiphase conditions is achieved by substituting the mixture fraction variable as representation of the composition in the original implementation of the turbulent flame speed closure model with independent species. Source terms to correlate the species progress to the reaction progress variable are derived in this work. The additional transport equations serve a higher generality of the model and enable the proper treatment of vaporizing fuel droplets. It is demonstrated that limitations which arise in the standard formulation of the model, stemming from differences in the transport equation for the reaction progress variable and the mixture fraction, are addressed and resolved by the new approach. Regarding the initiation of the flame, an additional source term for the reaction progress variable is introduced, which relates the reaction progress to the auto-ignition time. This allows the development of the flame without imposing artificial boundary conditions. The correct model behavior is established by means of a series of widely used test cases. The results of these simulations show that the model's potential to predict flame growth and more generally the flame evolution as a function of time and space is preserved. At the same time more sophisticated test case boundary conditions involving multiphase conditions and variable inflows in terms of composition can be incorporated. As a thorough assessment of the extended model capabilities, a multiphase lab scale set-up, which provides a comprehensive data set, is presented. The good agreement of the obtained results underline the range of applicability of the extended model and its accuracy, albeit its simplicity, for multiphase conditions.
机译：提出了湍流火焰速度闭合模型的扩展，使该模型适用于多相流和点火。由于以前除了通过层流火焰速度的温度依赖性之外，不存在反应进度变量和焓之间的耦合，因此提出了一种适应方法，该适应方法提供了引发燃烧过程的接口。合并多相条件的修改是通过将湍流火焰速度闭合模型的原始实现替换为具有独立种类的混合物分数变量作为组成的表示来实现的。这项工作推导了将物种进展与反应进展变量相关联的源术语。附加的运输方程式可为模型提供更高的通用性，并能够正确处理汽化的燃料滴。结果表明，新方法解决并解决了模型标准制定中由于反应进度变量和混合物分数的传输方程差异而产生的限制。关于火焰的引发，引入了用于反应进程变量的附加源术语，其将反应进程与自燃时间相关。这样可以在不施加人为边界条件的情况下产生火焰。通过一系列广泛使用的测试案例，可以建立正确的模型行为。这些模拟的结果表明，该模型保留了预测火焰增长的潜力，并且更广泛地预测了火焰随时间和空间的变化。同时，可以合并更复杂的测试用例边界条件，包括多相条件和成分变化的流入量。作为对扩展模型功能的全面评估，提出了提供全面数据集的多阶段实验室规模设置。获得的结果的良好一致性突显了扩展模型的适用范围及其准确性（尽管简单），适用于多相条件。

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