Basic Studies on Spray Formation Mechanism and Its Modeling

本研究的目的是从理论上和实验上阐明在喷嘴出口附近的液柱表面上产生的扰动波在周围空气剪切力作用下的解体过程，并在没有实验数据的情况下生成用于喷雾流动数值模拟的喷雾形成模型。首先，利用线性不稳定性理论得到了扰动波在液柱表面上的增长率随液柱与周围空气的相对速度变化的波数的函数。其次，通过照片观察了压电式陶瓷在喷嘴出口处的液柱振荡行为。用光片法测量了喷嘴出口喷雾浓度的波动，并用频域分析…得到了压电陶瓷的频率与喷雾浓度波动的关系在以上实验分析的基础上，建立了新的喷雾形成模型，并利用该模型计算了液柱破碎长度和液柱解体产生的喷雾的平均液滴尺寸。将计算结果与经验公式进行了比较。结果表明：(1)在对数对数图上，具有最大增长速率的扰动波的波长随相对速度的增加而线性减小。在对数对数图上，随着相对速度的增加，喷雾浓度的增长速度呈线性增加。(2)在平行气流中，液柱喷射时，喷雾浓度的波动分量在5 kHz附近存在低频分量，在10 kHz附近存在高频分量。当风速较大时，高频分量变得强烈。当风速较大时，频率分量全部出现。(3)用所提出的喷雾形成模型计算的喷雾破碎长度与经验公式基本吻合。除极小风速情况外，计算得到的平均液滴尺寸与经验公式基本吻合。较少

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