大攻角水下航行体自然空泡流的数值模拟研究

基于相分数输运方程型的均质平衡流空化模型,采用有限体积法研制了大型空泡流计算程序,对大攻角下运行的水下航行体三维空泡流进行了数值模拟,并与实验结果进行了对比.首次将非线性涡粘湍流模式与基于Rayleigh-Pies-set方程的TEM型空化模型相结合,建立了自然空泡流的数学模型.采用基于SIMPLE的压力-速度-密度耦合修正算法、二阶精度三时间层格式以及基于延迟修正的高阶对流TVD格式.计算模拟了0.2～0.6空化数、4°～20°攻角的不同工况,得到的三维空泡形状及压力分布与实验结果相符.研究了大攻角下航行体周向上的空泡形态分布特征,给出了多种空泡尺度和升阻系数与空化数和攻角之间的关系.通过定量分析发现,空泡的不对称性导致航行体某些部位受力集中,表明高速带空泡运动的航行体在大攻角运动中其结构将受到巨大的水动力载荷.计算还发现,大攻角下的阻力系数与空化数之间的关系和零攻角条件下刚好相反,并根据空泡的不对称性从形状阻力与粘性阻力的关系上对这种现象作出了解释.     

超空泡武器技术中的几个水动力学问题

综述了超空泡武器技术中的几个水动力学问题的研究进展.主要内容有超空泡武器的组成部分及对各部分的特殊要求;超空泡型态下物体的运动方式及其附加质量;空泡稳定性及其失稳机理;空泡闭合模型;超空泡型态下物体的水动力特性.最后对该领域的研究方向进行了展望.     

均匀流场中螺旋桨空泡数值模拟

在FLUENT软件中,采用多块结构化网格对业内选作标桨的E779A桨和PPTC桨进行了均匀来流下的空泡数值模拟。空泡模型采用基于输运方程的完整空化模型。研究表明:不可冷凝气体质量分数对空泡流场的计算结果影响较大。比较发现:数值预报的空泡形态,无论叶背部还是叶面部的片空泡,均与试验结果吻合较好;相同工况下所得螺旋桨推力系数、扭矩系数也与试验结果一致。     

空化器设计及超空泡参数控制

简要介绍了超空泡武器技术中有关超空泡空化器设计、空泡形状及压缩性的影响，以及通过调节通气率或改变空化器阻力，来实现超空泡参数控制等问题的研究进展，并对今后的研究方向进行了展望。     

Effect of elastic constitutive laws on the deformation of two-dimensional red blood cell

Deformation of two-dimensional red blood cell in linear shear flow is simulated using the immersed boundary method, in which the cell is modeled as a force source instead of a real body. The effect of three constitutive laws, i.e. Hookean, Neo-Hookean and Skalak elasticity, on the deformation is studied by simulating the cell movement in two linear shear flows. The results show that the effect of the constitutive laws gets more obvious as the shear rate increases. Both the aspect ratio and the inclination of the steady shapes get bigger, and the differences between the periods of the cell tank-treading motion become larger. For the same shear flow, the period with Hookean elasticity is less than the period with Neo-Hookean elasticity and bigger than the period with Skalak elasticity.     

Numerical investigation of characteristics of water-exit ventilated cavity collapse

The collapse of the ventilated cavitation occurring on a cylindrical vehicle during the water-exit is numerically researched. The numerical model employs the finite volume method to solve the multiphase Reynoldsaveraged Navier-Stokes (RNNS) equations and uses the volume of fluid (VOF) method to capture the free surface. A practical water wave environment that the vehicle usually encounters is reproduced in a numerical wave flume, so that the water wave’s effect on the cavity collapse flow regime is investigated. The main feature of the waterexit collapse of a ventilated cavity is studied under the wave-free condition. The result indicates that a collapsing ventilated cavity experiences two stages, in which the pattern of cavity evolution is different. In the early stage, the cavity undergoes a rapid shrinkage as a closed body. In the late stage, the cavity releases gas from the front due to the increase of the cavity pressure. The water wave effect is investigated at three typical wave phases: the wave crest, the wave trough and the wave node. Results show that when the vehicle is launched under the wave node, the cavity collapse regime remains fairly axisymmetric and is similar to the wave-free case. However, when the vehicle is launched under the wave crest and trough, the cavity evolution presents highly three-dimensional (3D) features. The results of predicted cavity size, pressure distributions and hydrodynamic forces at different wave phases show that the wave effect is relatively weak at the wave node but becomes apparent at the wave crest and trough.     

通气空泡流中洞壁效应对空化数和压力场影响的研究

文章在均质平衡多相流模型的基础上耦合输运方程型空化模型,通过求解混合介质的RANS方程、RNGk-ε湍流输运方程以及各相的质量输运方程,采用通用CFD软件-FLUENT数值模拟了水洞中带圆盘空化器航行体模型的定常通气空泡流动,研究了圆形截面闭式空泡水洞中洞壁效应对通气空化数和压力场的影响.得到的阻塞空化数线性正比于圆盘水洞直径比,且与三维圆盘自然空泡流的势流近似解基本一致,分析了洞壁效应作用下空化流场内的压力分布特点,并根据计算结果拟合了一定适用条件下通气空泡长度、最大直径和模型阻力系数的近似公式.     

Study on the characteristic of a forced pitching supercavitating vehicle

During the cruising of a supercavitating vehicle, the relative motion between the supercavity and the vehicle has a significant effect on the stability of the supercavity and the trajectory of the vehicle. In this paper,periodically forced pitching of a supercavitating vehicle is investigated numerically by a dynamic mesh method.The simulated result of the flow field around a pitching ventilated supercavitating vehicle in a water tunnel is compared with the experimental result. The evolution of the cavity morphology, the pressure distribution and the hydrodynamics of the vehicle are in good agreement with the experimental data. The effect of different pitching amplitudes and frequencies is studied. Also, the effect of the tunnel wall and the bracing structure is analyzed.     

TRANSIENT CAVITY COLLAPSE IN THE VICINITY OF A FLEXIBLE BOUNDARY

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四孔毕托管原理

本文提供了四孔毕托管的方案,用以测量三维流场。由于管数减少,它将减小探头的尺寸和减少测试的工作量。