MIMULTANEOUS MEASURING TECHNIQUE FOR INSTANTANEOUS CONCENTRATION AND VELOCITY AND ITS APPLICATION TO DIFFUSIVE-REACTIVE TURBULENCE

通过将双组分He-Ne激光多普勒测速仪与Ar^+激光诱导荧光技术相结合，开发了一种同时测量有化学反应和没有化学反应的湍流液体中浓度和速度的原始技术。通过同时测量湍流网格下游无剪切的液体混合层的浓度和速度，估计了质量通量和质量涡动扩散系数。此外，利用激光和电极电导相结合的技术，在具有二阶不可逆化学反应的同一湍流液体混合层中，同时测量了两种反应物质的瞬时浓度。为了研究湍流混合对平均反应速率的影响，从三个二级不可逆反应的瞬时浓度测量中估计了浓度相关性；反应分为极慢反应、中速反应和快速反应，并与几种闭合模型进行了比较。结果表明，该测量方法可以同时高精度地测量速度和浓度，而且对平均梯度扩散的近似计算在估计反应流体的质量通量时误差约为10%。在混合层的下游区域，偏析参数从-1向零增加，随着Damkohler数的增加，偏析参数趋于-1。修正后的3E闭合模型能较好地预测中速反应和快速反应的浓度相关性。拉格朗日随机模型可以明确地预测所有反应的浓度相关性，而不需要任何闭合假设，尽管它低估了相关性。此外，采用直接数值模拟（DNS）方法对液相和气相扩散反应机理进行了数值研究。三维纳维-斯托克斯和质量运输

An original technique for simultaneous measurements of concentration and velocity in a turbulent liquid flow with and without a chemical reaction was developed by combining a two-component He-Ne laser Doppler velocimeter with a Ar^+ laser-induced fluorescence technique. The mass flux and eddy diffusivity of mass were estimated from the simultaneous measurements of concentration and velocity in a liquid shear-free mixing layr downstream of a turbulence grid. Furthermore, instantaneous concentrations of two reacting species were simultaneously measured using a combined laser and electrode-conductivity technique in the same turbulent liquid mixing layr with second-order irreversible chemical reactions. To investigate the effect of turbulent mixing on the mean reaction rate, the concentration correlation was estimated from the instantaneous concentration measurements for three second-order irreversible reactions ; a very slow reaction, a moderately fast reaction and a rapid reaction, and it was compared with several closure models. The results show that the present measuring technique enables us to simultaneously measure velocity and concentration with high resolutions and that the approximation of the mean gradient diffusion causes about 10% error in estimating the mass flux in a reacting liquid flow. The segregation parameter increases from -1 towards zero in the downstream region of a mixing layr and it approaches to -1 with increasing the Damkohler number. The corrected 3E closure model can best predict the concentration correlation for both moderately fast and rapid reactions. The Lagrangian stochastic model can explicitly predict the concentration correlation for all reactions without suing any closure assumption, though it underestimates the correlation. In addition, the diffusive-reactive mechanism in both liquid and gas phases was numerically investigate using a direct numerical simulation (DNS). Three-dimensional Navier-Stokes and mass transportquation