Measurement of inter-scale molecular fluxes in supercritical reacting turbulence

了解湍流中特定长度尺度上的波动如何影响其他长度尺度上的现象，对于通过数值模拟准确预测流动特性至关重要。湍流燃烧是将化学能转化为热能用于运输和发电的主要模式，与无反应的湍流相比，湍流燃烧带来了额外的挑战，因为波动的化学反应速率发生在非常小的长度尺度上，通常无法通过模拟来解决。由于人们希望在越来越高的压力下运行燃烧系统，通常会跨越到超临界压力条件，因此这个问题更加严重。虽然增加压力对效率和功率密度有重要的好处，但它也会在越来越小的尺度上集中波动，并在临界点周围引入强烈的热力学性质变化。为了更好地理解这一现象，该项目将使用激光诊断和数据分析技术的新颖组合来测量初始超临界条件下预混火焰燃烧反应物中分子氮密度在长度尺度之间的波动。利用爆发模式自发拉曼散射在交叉平面上对空间过滤后的氮数密度和速度场进行时间分辨测量。观测过程的滤波效果将通过图像反卷积来确定和调整。因此，所得数据将允许根据滤波场的动态情况，明确确定通过滤波尺度的子滤波器波动通量。这些信息将确定传统的建模范式是否适用于超临界反应湍流，并在必要时能够开发出更精确的物理模型。它还将为超临界湍流燃烧的基准模拟提供一个独特的数据集。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Understanding how fluctuations at a specific length scale in a turbulent flow affect the phenomena at other length scales is critical to accurately predict flow properties by numerical simulation. In turbulent combustion, which is the predominant mode of converting chemical energy to thermal energy for transportation and power generation applications, additional challenges arise in comparison to non-reacting turbulent flows because the fluctuating chemical reaction rates occur at very small length scales that typically are not resolved by simulations. This problem is exacerbated by the desire to operate combustion systems at increasingly high pressures, often spanning in to the supercritical pressure conditions. While increasing the pressure has important benefits for efficiency and power density, it also concentrates fluctuations at increasingly small scales and introduces strong variations in thermodynamic properties around the critical point. To better understand this phenomenon, this project will use a novel combination of laser diagnostic and data analysis techniques to measure how fluctuations in molecular nitrogen density move between length scales in premixed flames burning reactants at initially supercritical conditions. Time-resolved measurements of the spatially filtered nitrogen number density and velocity fields will be made in crossed planes using burst-mode spontaneous Raman scattering. The filtering effect of the observation process will be determined and tuned through image deconvolution. Hence, the resultant data will allow explicit determination of the flux of sub-filter fluctuations through the filter scale based on the dynamics of the filtered fields. This information will identify whether traditional modeling paradigms hold for supercritical reacting turbulence and, where necessary, enable the development of more physically accurate models. It also will provide a unique data set against which to benchmark simulations of supercritical turbulent combustion.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.