Basic Studies on Spray Formation Mechanism and Its Modeling

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The purpose of this study is to clarify analytically and experimentally the disintegration process of disturbance waves generated on a liquid column surface near a nozzle exit by the shear force of the surrounding air, and is to generate the model of the spray formation which is used in the numerical simulation of a spray flow without the experimental data.At first, the growth rate of the disturbance wave on a liquid column surface was obtained by the linear instability theory as a function of the wave number with varying the relative velocity between the liquid column and the surrounding air. Next, the behaviors of the liquid column oscillated at the nozzle exit by the piezo-electric ceramic were observed by the photographs. The fluctuations of the spray concentration under the nozzle exit was measured by the light sheet method, and the relationship, between the frequency of the piezo-electric ceramic and that of the spray concentration fluctuation was obtained by the frequency analys … More is.Based on the results of above experimental analyzes, the model of the spray formation was newly developed, and the breakup length of a liquid column and the mean droplet size of the spray generated from the liquid column disintegration were calculated with using the proposed model. The calculation results were compared to the empirical equations. Consequently, the following results were obtained;(1) The wavelength of the disturbance wave with the maximum growth rate decreases linearly as the relative velocity increases on the log-log graph. The growth rate increases linearly as the relative velocity increases on the log-log graph.(2) In the case of the liquid column injection into the parallel air flow, at small air velocity the low frequency component near 5 kHz and the high frequency component near 10 kHz exit in the fluctuation component of the spray concentration. At large air velocity the high frequency component becomes intense. At further large air velocity all the frequency components appear.(3) The calculated breakup length using the proposed spray formation model is almost coincident with the empirical equation. The calculated mean droplet size almost coincides with the empirical equation except the condition of extremely small air velocity. Less