Abstract It has been predicted that several changes will occur when premixed flames are subjected to the extreme levels of turbulence that can be found in practical combustors. This paper is a review of recent experimental and DNS results that have been obtained for the range of extreme turbulence, and it includes a discussion of cases that agree or disagree with predictions. “Extreme turbulence” is defined to correspond to a turbulent Reynolds number (ReΤ, based on integral scale) that exceeds 2800 or a turbulent Karlovitz number that exceeds 100, for reasons that are discussed in Section 2.1 . Several data bases are described that include measurements made at Lund University, the University of Sydney, the University of Michigan and the U.S. Air Force Research Lab. The data bases also include DNS results from Sandia National Laboratory, the University of New South Wales, Newcastle University, the California Institute of Technology and the University of Cambridge. Several major observations are: (a) DNS now can be achieved for a realistic geometry (of the Lund University jet burner) even for extreme turbulence levels, (b) state relations (conditional mean profiles) from DNS and experiments do tend to agree with laminar profiles, at least for methane-air and hydrogen-air reactants that are not preheated, and (c) regime boundaries have been measured and they do not agree with predicted boundaries. These findings indicate that the range of conditions for which flamelet models should be valid is larger than what was previously believed. Additional parameters have been shown to be important; for example, broken reactions occur if the “back-support” is insufficient due to the entrainment of cold gas into the product gas. Turbulent burning velocity measurements have been extended from the previous normalized turbulence levels (u’/SL) of 24 up to a value of 163. Turbulent burning velocities no longer follow the trend predicted by Shchelkin but they tend to follow the trend predicted by Damkohler. The boundary where flamelet broadening begins was measured to occur at ReTaylor = 13.8, which corresponds to an integral scale Reynolds number (ReT) of 2800. This measured regime boundary can be explained by the idea that flame structure is altered when the turbulent diffusivity at the Taylor scale exceeds a critical value, rather than the idea that changes occur when Kolmogorov eddies just fit inside a flamelet. A roadmap to extend DNS to complex chemistry and to higher Reynolds numbers is discussed. Exascale computers, machine learning, adaptive mesh refinement and embedded DNS show promise. Some advances are reviewed that have extended the use of line and planar PLIF and CARS laser diagnostics to studies that consider complex hydrocarbon fuels and harsh environments.

中文翻译：

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受极端湍流影响的预混火焰：一些问题和最近的答案

摘要 据预测，当预混火焰受到实际燃烧器中可以发现的极端湍流水平时，将会发生一些变化。本文回顾了最近在极端湍流范围内获得的实验和 DNS 结果，并讨论了与预测一致或不一致的情况。“极端湍流”被定义为对应于超过 2800 的湍流雷诺数 (ReT，基于积分标度) 或超过 100 的湍流卡洛维茨数，其原因在第 2.1 节中讨论。描述了几个数据库，其中包括在隆德大学、悉尼大学、密歇根大学和美国空军研究实验室进行的测量。数据库还包括来自桑迪亚国家实验室的 DNS 结果，新南威尔士大学、纽卡斯尔大学、加州理工学院和剑桥大学。几个主要观察结果是：（a）即使对于极端湍流水平，现在也可以为（隆德大学喷气式燃烧器的）现实几何结构实现 DNS，（b）来自 DNS 的状态关系（条件平均剖面）和实验确实倾向于同意层流剖面，至少对于未预热的甲烷-空气和氢气-空气反应物，以及 (c) 区域边界已被测量，但与预测边界不一致。这些发现表明小火焰模型应该有效的条件范围比以前认为的要大。其他参数已被证明很重要；例如，如果由于冷气体夹带到产品气体中而导致“后支撑”不足，则会发生破坏反应。湍流燃烧速度测量值已从之前的归一化湍流水平 (u'/SL) 的 24 扩展到值 163。湍流燃烧速度不再遵循 Shchelkin 预测的趋势，但它们倾向于遵循 Damkohler 预测的趋势。测量火焰扩展开始的边界发生在 ReTaylor = 13.8，这对应于 2800 的积分尺度雷诺数 (ReT)。这个测量的区域边界可以通过以下想法来解释：当湍流扩散率在泰勒标度超过了临界值，而不是当 Kolmogorov 涡旋刚好适合小火焰时会发生变化的想法。讨论了将 DNS 扩展到复杂化学和更高雷诺数的路线图。百亿亿级计算机、机器学习、自适应网格细化和嵌入式 DNS 显示出前景。回顾了一些进展，这些进展已将线和平面 PLIF 和 CARS 激光诊断的使用扩展到考虑复杂碳氢化合物燃料和恶劣环境的研究。