NUMERICAL SIMULATIONS OF 2D PERIODIC UNSTEADY CAVITATING FLOWS

1. INTRODUCTION Cavitation is a natural phenomenon especially existing in liquids. A cavitating flow generally involves a large number of vapor structures such as bubbles or vortices which are convecting downstream. When they reach high pressure zones, th…     

波浪对水翼非稳态空泡流动特性的影响研究

基于雷诺平均Navier-Stokes方程、Singhal-Et-Al全空化模型和修正的RNG k-ε湍流模型的VOF多相流动数学模型,采用PISO算法的有限体积法和数值水池技术,对波浪作用下NACA0012水翼的非稳态空泡流动特性进行了数值研究,分析了波高和水翼浸深对水翼非稳态空泡的形态演化和脱落频率的影响.计算结果表明:空泡非稳态周期性脱落频率随波高的增加而增加,随水翼浸深的增加而逐渐减小.与无波情况相比,空泡在波谷处提前断裂,空泡形态也因为波谷下方速度场的影响而向上鼓起.由于自由液面的界面效应,空泡形态较无界情况偏扁,并且液面对脱落涡系有吸引作用.     

WATER TUNNEL EXPERIMENTAL INVESTIGATION ON THE DRAG REDUCTION CHARACTERISTICS OF THE TRAVELING WAVY WALL

Drag reduction experiment of the traveling wavy wall at high Reynolds number is conducted.A suit of traveling wavy wall device is developed.The drag forces of the traveling wavy wall with various wave speeds(c)are measured under different water speeds(U)in the K15 cavitation water tunnel and are compared with that of the flat plate.The results show that the mean drag force of the traveling wavy wall have decreased and then increased with oscillation frequency increasing at the same flow speed.Under different flow speeds,when traveling wave wall reached to the minimum of drag force,the corresponding the ratio of the wall motion phase speed c to flow speed U,c /U is slightly different.Within the parameters of the experiment,whenc /U reaches a certain value,the drag force of the traveling wavy wall can be less than that of the flat plate.The drag reduction can be up to 42%.Furthermore,as the value ofc /U increases,the traveling wavy wall can restrain the separation and improve the quality of flow field.     

APPLICATION OF QUADRATIC AND CUBIC TURBULENCE MODELS ON CAVITATING FLOWS AROUND SUBMERGED OBJECTS

Quadratic and cubic Non-Linear Eddy-Viscosity Models(NLEVMs) at low Reynolds number correction were introduced into the present Computational Fluid Dynamics(CFD) framework,to provide better numerical treatment about the anisotropic turbulence stress in cavitating flows,which have large density ratio and large-scaled swirling flow structures.The applications of these NLEVMs were carried out through a self-developed cavitation code,coupled with a cavitation model based on the transport equation of liquid phase.These NLEVMs were firstly validated by the benchmark of disk supercavity,and found able to obtain more accurate capture of the hydrodynamic properties than the linear models.One of such models was further applied on the cavitation problem of submerged vehicles.Ultimately,the supercavitating flows around an especially designed underwater vehicle were predicted using the cubic turbulence model,and its cavitation behaviors were studied.     

X80级管线钢管工程应用的几个问题

在对国内外大量文献和实际管道建设情况调研分析的基础上,结合国内X80级管线钢管的研究开发和产品试制结果,对我国管道界普遍关心的X80级管线钢管工程应用中的几个问题进行了论述.结果表明,采用高压输送及选用高钢级管材可以大量节约建设成本,是天然气管道发展的重要趋势.X80级已是国际上成熟的和标准的管线钢钢级,国际上在管道设计、生产、施工和运营等方面已有成熟经验.国内经过几年的研究开发首批试制的X80级管线钢管质量指标满足要求严格的X80级管线钢管应用工程标准要求,钢管实物质量与国外同类产品处于同一水平.国际上对输送普通天然气的X80级管道的断裂控制问题已经解决,根据对X80级管道启裂韧性和止裂韧性的分析研究及管道运行安全性的分析,用减薄壁厚的X80级替代X70级是安全的,也是可行的.未来X80级管线钢管在国际上的应用将会越来越广泛.实施X80级管线钢管工程应用是十分必要的.建议在未来大口径高压输气管线中优先选用X80级管线钢管.     

潜射导弹尾部燃气后效建模及数值模拟

利用Rayleigh-Plesset方程,建立了等压球状尾泡模型,分析了尾泡的泡内压力变化.通过尾泡方程与导弹运动方程的联合求解,讨论了燃气泡对垂直发射潜射导弹弹道轨迹的影响.结果表明,导弹在出筒后,由于环境压力的变化,尾部压强有小幅波动,随着尾泡尺寸的减小,波动周期越来越短,与试验测量结果吻合较好.     

环焊缝强度匹配对长输管道性能的影响

环焊缝强度匹配是天然气管道研究与应用的热点问题.介绍了焊接接头匹配性的概念,阐述了不等强匹配对长输管道极限载荷、韧性、残余应力、缺陷容限等的影响,最后提出了在长输管道环焊缝强度匹配领域需要解决的技术问题.     

绕二维对称水翼的通气空泡流数值研究

本文通过有限体积离散方法求解Reynolds平均Navler—Stokes方程，采用VOF法追踪气一液两相交界面。研究了在高压低速来流，即本质上不发生自然空化的条件下，绕二维对称水翼的非定常通气空泡流动。分析了物理参数——通气方向角和攻角，对通气空泡外形、稳定性及水动力参数的影响。计算结果表明：在通气空泡的形成过程中，通气方向角存在着一个临界值，使得空泡形态由片状空泡过渡到超空泡；特定的参数组合将会诱发空泡表面出现波动现象。而且，当攻角做周期性变化时，水动力参数的变化也随之满足周期性规律，且出现阶段性振荡。     

通风机空气动力性能通用测试软件的设计与实现

设计了通风机空气动力性能通用测试软件,详细叙述了测试软件的设计方案;利用C#.NET开发了实时测试软件,可对实验室传感器状态进行实时监控,并通过串行口来实现计算机与中央控制系统的实时通信。在不同的设定下,可实现不同的试验装置类型和流量测量方式的测试目的。实际应用表明,该测试软件实用性强,运行稳定可靠。     

MODELLING AND COMPUTATION OF UNSTEADY TURBULENT CAVITATION FLOWS

1. INTRODUCTION Cavitatating flows are important phenomena happened in industry setups and many under-water vehicles. It leads to performance losses and modifications of blade load when happened in machines, especially turbo-machinery. Nevertheless, cavit…