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A flamelet-based relaxation model for polycyclic aromatic hydrocarbons in turbulent flames

机译：基于湍流芳烃烃的基于爆炸式弛豫模型

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In this paper, the response of different species to turbulent unsteadiness is investigated utilizing the 1D unsteady laminar diffusion flamelet model. Turbulent effects are modeled solely through a abrupt change in the scalar dissipation rate. Steady-state flamelets are perturbed by the modeled turbulent effects. One-dimensional flamelet calculations assuming unity-Lewis number for all species are performed. Based on the numerical results, relations between the chemical source terms and species mass fractions are examined for various representative species. It is found that the smallest turbulent time scale remains much larger than that of the gaseous phase chemistry for some small species. The steady-state flamelet assumption for these species is well justified and their mass fractions can be pre-tabulated using the flamelet library legibly. On the other hand, PAH chemistry is relatively slow, and these PAH species cannot react instantaneously to the abrupt change in the local scalar dissipation rate. Based on the above considerations, a relaxation model is proposed for the chemical source terms of light species, species of moderate molecular weights, and heavy hydrocarbons. These source terms can be decomposed into a positive production term and a negative consumption term. The production term is observed to be constant for a given mixture fraction value, whereas the consumption term is found to be linearly dependent on the local species concentration. The dependence of the consumption term on the species mass fraction is found to be determined only by the scalar dissipation rate after its abrupt change. This observation suggests that the relaxation model can be fully pre-tabulated using the results of steady state flamelets. Based on the relaxation results, the validity of different chemistry tabulation models is assessed.
机译：本文利用1D非稳态层状扩散爆震模型研究了不同物种对湍流不稳定性的响应。湍流效应仅通过标量耗散率的突然变化进行建模。稳态挥动物由模型的湍流效应扰乱。执行假设所有物种的Unity-Lewis编号的一维轰炸机计算。基于数值结果，检查化学源术语和物种质量分数之间的关系，用于各种代表性物种。结果发现，对于一些小物种，最小的湍流时间尺度保持大于气相化学的时间。这些物种的稳态脉动假设很好，并且它们的质量级分可以用挥动图谱清晰地预先形成。另一方面，PAH化学相对较慢，这些PAH物质不能瞬间反应，以局部标量耗散率的突然变化。基于上述考虑，提出了一种弛豫模型，用于光种的化学源，中等分子量和重质烃类化学源。这些源术语可以分解为正生产术语和负消耗项。观察到生产术语对于给定的混合物级分值是恒定的，而发现消耗项被发现线性地取决于局部物种浓度。发现消费项对物种质量分数的依赖性仅被突然变化后的标量耗散率确定。该观察表明，可以使用稳态挥发物的结果完全预先制成松弛模型。基于放松结果，评估了不同化学制表模型的有效性。

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