Development of Simultaneous and Instantaneous Measurement of Two-Dimensional Velocity Vectors and Scalar Profiles by Advanced Laser Image Diagnostics

火焰的行为受化学反应和湍流相互作用的影响，因此获得瞬时二维流体速度分布以及温度和/或物质浓度分布有助于了解湍流火焰的微观结构特征。采用瑞利散射成像测速（RIV）和氢氧激光诱导荧光（OH- lif）相结合的方法，对湍流氮气-氢（H_2 30% + N_2 70%）扩散火焰中二维温度、氢氧浓度和速度矢量分布进行了瞬时和同步测量。这种测量方法使我们能够估计应变速率、温度和沿火焰表面OH浓度，这是通过追踪峰值OH浓度得到的，并研究湍流扩散火焰的局部行为。根据OH- lif强度定量测量OH浓度，并考虑OH- lif淬火数据库进行校准。通过速度矢量和OH浓度分布估计了沿火焰表面（OH峰反应区）的应变速率。本研究得到的结果如下：(1)当火焰向中心线倾斜，应变率变为正高时，火焰中局部温度和OH浓度趋于下降。另一方面，局部温度和OH浓度较高的火焰往往没有正应变率和高应变率。(2)当火焰表面被侧向对流运动向外推进时，OH浓度峰的径向位置倾向于位于温度峰的显著外侧。它们的轮廓与层流火焰的轮廓有很大的不同。与层流火焰相比，在火焰没有正应变率和高应变率的地方观察到相当高的OH浓度。

The behavior of the flamelet is affected by the interaction between chemical reaction and turbulence and so it is useful to get instantaneous two-dimensional fluid velocity profiles together with the temperature and/or species concentration profiles to understand the characteristics of microscopic structure of the turbulent flames. In this study, by combining Rayleigh Scattering Image Velocimetry (RIV) with OH Laser Induced Fluorescence (OH-LIF), instantaneous and simultaneous measurements of two-dimensional temperature, OH concentration and velocity vectors profiles were made in a turbulent nitrogen-diluted hydrogen (H_2 30% + N_2 70%) diffusion flame. This measuring method enables us to estimate strain rate, temperature and OH concentration along the flame surface, which is obtained by tracing peak OH concentration, and to investigate local behavior of turbulent diffusion flames. OH concentration was measured quantitatively based on OH-LIF intensity and the calibration considering the OH-LIF quenching database. The strain rate along the flame surface (reaction zone of OH peak) was estimated by the velocity vectors and OH concentration profiles. The results obtained through this study are as follows. (1) Local temperature and OH concentration depression in the flame tends to occur when the flame inclines toward the centerline and the strain rate becomes positive and high. On the other hand, the flame that has locally high temperature and OH concentration tends no to have positive and high strain rate. (2) When the flame surface is pushed outward by the lateral convection motion, the radial position of OH concentration peak tends to be located prominently outside of the temperature peak. Their profiles are much different from those of the laminar flame. The considerably high OH concentration as compared with the laminar flame was observed where the flame does not have positive and high strain rate.