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

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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