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

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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.