Periodic Structures in Pool Fires

已经观察到，在中等规模的火灾底部形成了大型的旋涡结构，并随着燃料和空气的相互消耗而向上传播。本研究旨在了解这些结构是如何以及为什么形成的，量化它们对空气夹带和燃料燃烧速度的影响，并确定池火、强浮力非反应射流和加热水平表面上的自然对流在近场流体力学中的异同。同时测量了一个大型低速氦射流垂直流向空气中多个位置的浓度和速度波动，以模拟池火。在直径近一米的燃烧酒精池上方，也测量了温度和速度的波动。非反应体系的三维瞬态数值模型正在开发中，以解释实验结果。研究结果将为池火的定量预测提供依据。因为它将基于对中型羽流实验结果的基本解释，这种理解也将适用于更大尺度的火灾，这是社会经常关注的问题（泄漏，燃料箱等）。

Large vortical structures have been observed to form at the base of moderate sized fires and to propagate upwards as the fuel and air are mutually consumed. This research seeks to understand how and why these structures form, to quantify their effect on the entrainment of air and the burning rate of the fuel, and to identify the similarities and differences in the near-field fluid mechanics among pool fires, strongly buoyant nonreacting jets, and natural convection above heated horizontal surfaces. Simultaneous measurements are made of the fluctuating concentration and velocity at multiple locations inside a large, low speed helium jet flowing vertically into air to simulate a pool fire. The fluctuating temperature and velocity are measured also above burning alcohol pools up to nearly one meter in diameter. A three-dimensional, transient numerical model of the nonreacting system is being developed to interpret the experimental results. The results of this research will provide a quantitative basis for the prediction of pool fires. Because it will be based on the fundamental interpretation of results from medium-sized plumes experiments, such understanding will be applicable also to fires of larger dimensions, which are of frequent concern to the community (spills, fuel tanks, etc...).