【作者】 李梦圆；

【导师】 付强； 朱荣生；

【作者基本信息】 江苏大学 ， 动力工程及工程热物理， 2018， 硕士

【摘要】 本文针对气核参数与壁面特性对二维水翼空化比尺效应的机理进行研究,以NACA4412翼型为研究对象,研究绕不同尺寸翼型流动产生的空化比尺效应进行研究,首先对平行壁面间液氩中空化过程的异质成核进行研究,然后将微观空泡理论研究成果联系到简化的二维翼型空化过程中,研究了二维水翼空化过程中的比尺效应现象,具体研究内容如下:1.采用微观分子模拟手段研究平行铂壁面间液体氩中空化核的瞬态特性。对壁面间一定尺寸稳定存在的空化核进行不同拉伸和不同壁面润湿性研究,对空化核的生长、系统压力和系统总压力进行分析。结果表明系统Pt壁面间稳定存在的空化核生长状况与系统的亚稳态程度及壁面润湿性息息相关。壁面的拉伸距离存在临界值,大于临界值的拉伸造成系统的不稳定性程度越大,从而利于空化核的生长,空化约剧烈。相对于疏水性壁面间的空化核体积缩小,亲水性壁面间的空化核体积明显增大,更利于空化核的生长,利于空化核的自发生长行为,而疏水性壁面对空化核有抑制作用,联系宏观空化现象,壁面的亲水性越强在壁面产生的初生空化数越多,越利于空化的发生。2.对弦长分别为75、100、150mm的三个NACA4412水翼进行数值模拟分析,研究空化初生、发展、溃灭、再生的非定常流动过程。结果表明在空化初生阶段,150mm弦长的翼型空化初生现象最为剧烈,结合微观壁面空化研究,得出尺寸越大的翼型前缘低压区强度越强,系统失稳程度的增大越利于空化核生长,所以当来流中气核数相同时,尺寸大的翼型越利于提高初生空化的产生。并且验证了翼型表面空化尾部脱落与翼型尺寸的关系,不同尺寸下空泡尾部高压区对主体空化的推挤强度不同,造成各自空化回缩距离不相同,尺寸越小情况下的主体空泡回缩距离越小。翼型尺寸大小也决定着绕翼型流动的空化非定常脉动频率,在相同空化数条件下,不同尺寸翼型的空化非定常脉动周期时间与翼型尺寸呈正相关。3.对三种尺寸的NACA4412翼型进行空化试验研究,分析了不同空化数情况下,不同尺寸翼型间空化比尺效应的差异,分析结果表明初始空化数的大小对空化比尺效应的影响在于:空化过程的形貌、再生空化的出现。而试验结果与数值模拟结果之间的差异是由不同粗糙度表面以及流体介质中不凝结气体含量不同导致。更多还原

【Abstract】 In this work,the mechanism effect of the cavitation scale in two-dimensional hydrofoil is studied in terms of the gas core parameters and the wall surface.Taking the NACA4412 hydrofoil as the research object,the cavitation scale effect resulting from the flow of different hydrofoil size is studied.The heterogeneous nucleation of the liquid argon cavitation process between parallel walls was studied,and then the microcavity theoretical research results were connected to a simplified two-dimensional hydrofoil cavitation process,and the scale of the two-dimensional hydrofoil cavitation was studied.The main research contents are as follows:1.The microscopic molecular simulation is used to study the transient characteristics of liquid argon cavitation nuclei between parallel platinum walls.The cavitation nucleus with a certain size and stably existing between the wall surfaces was subjected to different tensile and different wall wettability studies,and the cavitation nucleus growth,system pressure and total system pressure were analyzed.The results show that the steady state of cavitation nucleus growth in the Pt wall is closely related to the system’s metastable state and wall wettability.There is a critical value for the stretching distance of the wall surface,and the instability degree of the system caused by the stretching above the critical value is greater,thereby facilitating the growth of the cavitation nucleus,and the cavitation is about to be severe.Compared with the shrinkage of the cavitation nucleus between the hydrophobic walls,the nucleation volume between the hydrophilic walls increases significantly,which is more conducive to the growth of the cavitation nucleus,which facilitates the spontaneous growth of the cavitation nucleus,while the hydrophobic wall faces the void.The nuclear nucleus has inhibitory effects and macroscopic cavitation phenomenon.The stronger the hydrophilicity of the wall surface is,the more primary cavitations are generated on the wall surface,which is more beneficial to the occurrence of cavitation.2.Numerical simulation analysis was performed on three NACA4412 hydrofoils with chord lengths of 75,100,and 150 mm,respectivelyto study the unsteady flowprocess of cavitation initiation,development,collapse,and regeneration.The results show that in the initial stage of cavitation,the initial cavitation phenomenon of the150 mm chord-length hydrofoil is the most intense.Combined with the microscopic cavitation study,it is concluded that the larger the size of the hydrofoil leading edge low-pressure region is,the stronger the intensity is,and the degree of system instability increases.Larger is more conducive to cavitation nuclear growth,so when the number of air cores in the same flow,the larger size of the hydrofoil is more conducive to the generation of primary cavitation.The relationship between the cavitation tail shedding and the hydrofoil size on the surface of the hydrofoil was verified.The different cavitation tail high pressure zones had different push strengths for the main cavitation,resulting in different cavitation retraction distances and the smaller the size.The smaller the body’s vacuole retraction distance is.The size of the hydrofoil also determines the unsteady pulsation frequency of the cavitation flow around the hydrofoil.Under the same cavitation number conditions,the unsteady pulsation cycle time of the hydrofoil of different sizes is positively related to the hydrofoil size.The cavitation test in three NACA4412 sizes hydrofoil is studied.The difference of the cavitation scale effect between different sizes of hydrofoil is analyzed under different cavitation numbers.The analysis results show that the size of the initial cavitation number is related to cavitation.The effect of the scale effect lies in the appearance of the cavitation process and the appearance of regeneration cavitation.The difference between the experimental results and the numerical simulation results is caused by different roughness surfaces and different non-condensable gases in the fluid medium.更多还原