Modeling of Spray Formation Mechanism and Numerical Simulation of Spray Flow

本研究的目的是澄清使用平面射流雾化器的液体射流的解体过程，并模拟液体射流表面上的扰动波的起始和扰动波的增长过程。本研究的最终目标是完成一个通用的喷雾流数值模拟算法，包括喷雾形成机理模型。首先，采用数值模拟的方法研究了雾化器内液体流动的涡特性对液体射流表面扰动波起始的影响。用朗肯涡模拟了液体流动中的旋涡。得到了以下结果：涡的旋转方向，其中液体射流表面减速，影响很大的波的起始。表面扰动波的波长取决于具有上述旋转方向的涡之间的距离。第二，液滴从液体射流表面脱离的事实是由于液滴的运动引起的。 ...更多信息 通过对喷雾形成过程的观测，阐明了液体射流在喷雾形成过程中所产生的小扰动波的增长和液体射流本身由于增长了一个相对较大的非轴对称波而解体的机理，并在此基础上提出了喷雾形成机理模型。在整个波数范围内的各个轴对称波都与液体射流表面的喷雾形成有关。射流破碎过程中出现的具有最大增长率的非轴对称波与射流本身的破碎有关。用该模型对液滴形成过程进行了数值模拟，结果表明，除完整核长外，数值模拟结果与实验结果吻合较好。最后，利用所提出的喷雾形成机理模型对喷雾流场进行了数值模拟。预测的风速、液滴速度、液滴平均直径与实测值吻合较好。然而，液滴分散被低估。这种差异可以归因于液滴初始速度的估计和液滴湍流扩散模型。在未来，雾化器中的液体流动中的湍流与液体表面上的扰动波特性之间的关系的建模应该是必要的。少

This study aims to clarify the disintegration process of a liquid jet using a plain-jet atomizer and to model the disturbance wave inception on a liquid jet surface and the growth process of disturbance waves. Final target of this study is to complete an universal numerical simulation algorithm of spray flow including a model of spray formation mechanism. Firstly, the influences of the characteristics of vortices in the liquid flow in an atomizer on the disturbance wave inception on a liquid jet surface, were investigated using a numerical simulation. The vortex in a liquid flow was simulated by a Rankine vortex. The following results were obtained ; The vortex with a rotational direction in which a liquid jet surface is decelerated, affects greatly the wave inception. The wavelength of the disturbance waves on the surface is determined by the distance between vortices with above rotational direction. Secondly, the facts that the detachment of droplets from the liquid jet surface is ca … More used by the growth of small disturbance waves on the surface and the liquid jet itself is disintegrated due to the growth of a relatively large non-axisymmetric waves, were clarified by the observation of the spray formation process.Based on the observation, the model of spray formation mechanism was proposed. The each axisymmetric wave within whole wave number range is concerned in the spray formation from the liquid jet surface. And the non-axisymmetric wave with maximum growth rate is concerned in liquid jet disintegration itself. The numerical simulations of the droplet formation using the proposed model showed good agreements with theexperiments except intact-core length. Finally, the numerical simulations of the spray flow using the proposed model of spray formation mechanism were carried out. The predicted air velocity, droplet velocity, droplet mean diameter were coincident moderately with the measurements. However, the droplet dispersion was under-estimated. This discrepancy can be contributed to the estimation of a droplet initial velocity and the droplet turbulent dispersion model. In a future, the modeling of the relationship between the turbulence in the liquid flow in an atomizer and the disturbance wave characteristics on a liquid surface, should be necessary. Less