# Review on the Recent Numerical Studies of Liquid Atomization
Other applications of liquid atomization that focus most on the spray far from the nozzle exit include spray systems to crop-dust or irrigate agriculture plants and cooling towers used for electricity production [13]. Droplets' secondary breakup, collision, and coalescence are therefore important even in the far region from the nozzle, and their mechanisms must be taken care of when modeling this kind of liquid atomization. Liquid atomization is one important type of gas-liquid multiphase flows. Different from internal gas-liquid flow, where a combination of two streams of particular speed usually corresponds to one flow pattern and thus all the macroscopic features like heat transfer and pressure drop can be evaluated [14], atomization shows varying patterns in a tiny space while having significant impact on the downstream spray evolution. Not only do the physical characteristics and flow speeds of the fluids influence the atomization pattern, but also the historical flow conditions, including the turbulence upstream and the nozzle shape, play a critical role. Description and division of the atomization regimes and mechanisms are still in development, and some controversial conclusions exist. Predictions of shape of the spray as well as distributions of droplets size and velocity are also research objectives of liquid atomization. No matter what the liquid is (liquid metal or non-metal, combustible or not) and what kinds of nozzle, the micro phenomena the moment after the liquid is ejected out resemble each other. Also, the difficulties encountered when exploring these phenomena are also similar, such as the measurement of the dense region of the spray when trying to capture its high-resolution temporal and spatial evolvement. Fortunately, numerical simulation can act as a good substitute, possessing superiority over experimental observation in aspects of obtaining massive detailed temporal evolution of micro interface structure, although currently it requires huge computer resources unacceptable for practical use, in addition to the questionable accuracy of various models. Numerical exploration provides measures to obtain details of the atomization that otherwise would be hard or impossible and helps to make certain serval atomization mechanisms. However, the current various numerical methods adopt inconsistent fundamental models and sometimes result in discrepancy among each other. Moreover, some methods cost huge computer resources, which is impossible for design purposes even within the foreseeable prosperous development of computer technology. The aim of the present review is to provide a general idea of the capabilities of modern computer technology and numerical models in aspects of simulating atomization and designing relative devices and to hopefully guide the future research to strive toward efficient and productive methods. This paper is divided into eight sections. After this first introductory part, the general characteristics of liquid atomization including the different regimes for nozzle of various types are discussed in Section 2. Then, five main numerical frameworks including interface capturing, particle tracking, hybrid of interface capturing and particle tracking, multi-fluid and multi-scale Eulerian method, and smoothed particle hydrodynamics method are illustrated in sequence from Section 3 to Section 7, where their respective numerical kernels of primary and secondary breakup as well as some representative simulation cases are summarized. The possible subsequent evaporation, combustion, or solidification will not be considered, since this paper focuses on the atomization itself. Finally, the future research focus and orientation are suggested in Section 8.