筒口水气混合流场对空泡影响的数值研究

发布时间：2018-07-25 08:35

【摘要】：水下航行体上的附着空泡极大的改变了周围流场结构,对航行体的水动力性能有重要影响,因此受到学者的广泛重视。在试验中发现,当航行体在水下用高压气体从发射筒中弹射出去时,航行体穿越的并不是静止的单一水介质流场,而是筒口泄气射流与周围水流体相互掺混后的非定常水汽混合复杂流场。航行体在这种水气掺混流场中的空化与单一水介质中有很大不同,空泡在航行体上的产生、附着及演化过程受到水气掺混流场结构的重大影响,随之也对航行体的水动力及弹道带来复杂变化。目前对空泡开展的研究,多是针对单一水介质中的空泡,而对水气混合流场诱发的空泡,尚未进行综合研究。因此,对这方面开展研究具有重要的工程应用价值。水气掺混的流场结构复杂多样,其中既有掺混比较均匀的流动,也含有大大小小气泡的流动,不同流动结构对空泡发展有不同的影响。为了简化机理研究,本文将对水气掺混结构简化为两种典型的基本结构:一是水气掺混均匀的单相结构,二是具有明显水气分界面的大气泡结构;然后利用数值模拟方法,分别研究了航行体穿越这两种水气混合流场结构的空泡产生、演化发展及水动力特性。航行体穿越水气均匀混合流场时,空泡受速度与含气率的综合影响。由于水气混合介质的声速下降很大,在水汽混合流场中有可能出现超声速流动,航行体上不仅会出现空泡,而且还会产生激波。激波与空泡发生相互作用,结论是:航行体头部前面产生的脱体激波削弱了空化效应,使得空化区域减小;受空泡外形影响,空泡分离面位置产生膨胀波,而空泡末端出现弯曲形状的斜激波;当含气率超过一定值,空泡将闭合在斜激波面上而不是航行体表面上,体现在空泡尾端壁面逆压梯度趋于平缓,没有明显的闭合高压出现。航行体穿越筒口泄气产生的膨胀气泡时,气泡在一定条件下有可能附着在航行体上形成附着空泡。通过研究不同头型航行体穿越气泡的过程发现,头型对气泡附着过程的影响极大:对于易空化的钝头型,气泡容易附着在航行体上形成附着空泡。对于不易空化或细长头型,气泡受到扰动后就很快与航行体分离。文中初步分析了气泡的附着机理和条件。以上研究可对航行体的外形设计及水动力预报提供参考。
[Abstract]:The attached cavitation on the underwater vehicle greatly changes the structure of the surrounding flow field and has an important influence on the hydrodynamic performance of the vehicle. Therefore, the scholars pay much attention to it. In the experiment, it is found that when the vehicle ejected from the launching tube with high pressure gas under water, the navigation body was not a static single water flow field. It is a complex flow field of unsteady water vapor mixed with the mixing of the deflated jet and the surrounding water fluid. The cavitation in this water and gas mixing field is very different from that in a single water medium. The formation of the cavitation on the vehicle, the process of attachment and evolution is greatly influenced by the structure of the mixed flow field of water and gas, and then to the navigation body. Hydrodynamics and ballistics bring complex changes. At present, the research on vacuoles is mostly aimed at the vacuoles in a single water medium, but it has not been studied synthetically for the vacuoles induced by the mixed flow of water and gas. Therefore, it is of great engineering application value to carry out this research. The flow structure of the mixture of water and gas is complex and diverse, in which the mixing ratio is not only complex. In order to simplify the mechanism study, this paper will simplify the mixing structure of water and gas into two typical basic structures: one is the homogeneous single-phase structure with water and gas mixing, and the two is a large bubble structure with obvious water and gas interface; The numerical simulation method is used to study the bubble generation, evolution and hydrodynamic characteristics of the two kinds of water vapor mixed flow field structure. The cavitation is influenced by the velocity and gas content when the vehicle passes through the homogeneous mixed flow field of water and gas. The supersonic flow can occur, not only the cavitation appears on the vehicle, but also the shock waves. The shock wave is interacting with the vacuoles. The conclusion is that the detachment shock produced in front of the head of the vehicle weakens the cavitation effect and reduces the cavitation area, which is influenced by the shape of the vacuoles, and produces the expansion wave in the position of the vacuolar separation surface, and the end of the vacuoles appears. When the gas content exceeds a certain value, the bubble will be closed on the oblique shock surface rather than on the surface of the vehicle, and the reverse pressure gradient tends to be slow, and there is no obvious closed pressure. The bubbles may be attached to the air under certain conditions. An attachment cavitation is formed on a row. Through the study of air bubbles through different head types, it is found that the head type has a great influence on the process of air bubble attachment: for the blunt type of easy cavitation, the bubbles easily attach to the aircraft to form an attached vacuole. For the air bubbles that are not easy to be cavitation or slender head, the bubbles are quickly separated from the aircraft. The mechanism and conditions of bubble attachment are preliminarily analyzed. The above research can provide reference for the shape design and hydrodynamic prediction of the vehicle.
【学位授予单位】：中国舰船研究院
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U661.1

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