Images of Local Propagation Speeds and Stretch Rates of Turbulent Premixed Flames to Improve Numerical Models

Driscoll CTS-9904198这是一项首次量化湍流预混火焰表面局部传播速度的实验研究。当在起皱的火焰表面形成凸起和尖端时，某些火焰段以异常大的速度向前传播。用PIV-PLIF(粒子成像测速-平面激光诱导荧光)诊断技术测量了非定常、弯曲的二维层流火焰的传播速度。在这项研究中，这项技术被推广到三维(3-D)的情况下，使用两套正交的激光光片。这项工作包括：(A)测量沿着湍流火焰表面的局部传播速度；(B)测量3-D火焰延伸率；(C)识别火焰锋面中产生异常大的局部传播速度的尖端和凸起，并调查这些异常的物理原因；图像允许将快速火焰传播与涡旋的存在、火焰曲率或火焰片段之间的共用自由基相关联；(D)将测量的传播速度与来自不同组的高级直接数值模拟的结果进行比较；与火焰应力理论预测的结果相比，局部传播速度是建立预混和部分预混燃烧大涡模拟的关键参数。这些模型提供了在湍流燃烧方面取得重大新突破的可能性，包括开发低污染的燃气轮机和内燃机。

ABSTRACTJAMES F. DRISCOLL CTS-9904198This is an experimental study to quantify, for the first time, the local propagation speed along the surface of a turbulent, premixed flame. As bulges and cusps form on the wrinkled flame surface, certain flame segments propagate forward at unusually large speeds. A PIV-PLIF ( particle imaging velocimetry- planar laser induced fluorescence) diagnostic has been used to measure propagation speed for an unsteady, curved, two-dimensional laminar flame that undergoes a flame-vortex interaction. In this study, this technique is extended to the three-dimensional (3-D) flame case by using two sets of orthogonal laser light sheets. The effort includes (a) measurements of local propagation speed along a turbulent flame surface; (b) measurements of 3-D flame stretch rates; (c) identification of cusps and bulges in the flame front that yield abnormally large local propagation speeds and investigation of the physical reasons for these abnormalities; images allow correlation of fast flame propagation with the presence of a vortex, with flame curvature, or with the sharing of radicals between flame segments; (d) comparison of measured propagation speeds to those from advanced direct numerical simulations (DNS) from various groups; and to those predicted by the Theory of Flame Stretch.Local propagation velocity is the key quantity that must be correctly modeled in order to develop large-eddy simulations (LES) of premixed and partially premixed combustion. Such models offer the possibility of major new breakthroughs in turbulent combustion, including the development of low-polluting gas-turbine and internal-combustion engines.