基于CFD方法的船/桨/舵干扰数值模拟

船/桨/舵相互干扰研究在传统船型优化设计和新船型的开发中具有重要意义。应用计算流体力学(CFD)方法对带桨的KCS集装箱船及带桨和舵的KVLCC2油船非稳态粘流场进行了数值模拟,其中船桨舵干扰计算分别采用动量源法、MRF法和滑移网格法,分析研究了各方法及其结果的异同。研究表明不同模拟计算方法均能合理预报出船/桨/舵相互干扰相互作用下速度场和压力场分布等详细流场信息,可用于计算船体阻力、表面压力和桨盘面伴流等。通过这种详细的数值模拟研究,可以更好地理解复杂流动干扰现象。     

丁坝水流的水槽试验及数值模拟研究

该文进行了丁坝绕流水槽试验,采用测压管和激光多普勒测速仪(LDV)测量了正交绕流单丁坝附近的水位和流速,同时利用商用软件CFX,基于有限体积法,采用k-ε湍流模型,数值模拟了丁坝附近水流的三维流动过程,并将水槽试验结果与数值模拟结果进行了对比分析.实验结果表明,该模型能有效地模拟丁坝附近区域复杂的水流特征,可以在河道整治过程中为丁坝的设计提供基础数据.     

On the numerical simulations of vortical cavitating flows around various hydrofoils

This paper reviews the numerical models of various cavitating flows around hydrofoils. Numerical models relating to cavitation flows, including mass transfer models and turbulence models, are summarized at first. Then numerical results and analysis of flow characteristics for the cavitating flows around twisted hydrofoils, truncated hydrofoil and tip leakage are discussed respectively. For mean flow fields, Reynolds averaged Navier-Stokes(RANS) simulation associated with a kind of nonlinear turbulence model is found to be an economic and robust numerical approach for different kinds of cavitating flows including cloud cavitation, tip cavitation and tip leakage cavitation. To predict the fluctuations of pressure and velocity, large eddy simulation(LES) and detached eddy simulation(DES) are two effective approaches. Finally, a few open questions are proposed for future research.     

Three-dimensional numerical simulation of flow around a circular cylinder under combined steady and oscillatory flow

Combined steady and oscillatory flow past a circular cylinder is investigated numerically by three-dimensional Direct Numerical Simulation (DNS). The incompressible Navier-Stokes equations are solved by finite element method (FEM). The aim of this study is to investigate influence of the existence of steady current on the flow regime and hydrodynamics forces. The computational results of pure oscillatory flow past a circular cylinder agree well with the experimental data. The flow ratios (ratio of current velocity to oscillatory velocity amplitude) are 0.0, 0.2 0.5 and 1.0 in the study. The influence of the flow ratio on the vortex shedding regime and hydrodynamic forces on the cylinder are investigated numerically.

     

Some notes on numerical simulation and error analyses of the attached turbulent cavitating flow by LES

In this letter, the attached turbulent cavitating flow around the Clark-Y hydrofoil is investigated by the numerical simulation with special emphasis on error analysis of large eddy simulation(LES) for the unsteady cavitation simulation. The numerical results indicate that the present simulation can capture the periodic cavity shedding behavior and show a fairly good agreement with the available experimental data. Further analysis demonstrates that the cavitation has a great influence on LES numerical error and modeling error. The modeling error and numerical error are almost on the same order of magnitude, while the modeling error often shows a little bit larger magnitude than numerical error. The numerical error and modeling error sometimes can partially offset each other if they have the opposite sign. Besides, our results show that cavitation can extend the magnitudes and oscillation levels of numerical error and modeling error.     

平面网衣周围流场的三维数值模拟

采用Realizable kε湍流模型,结合多孔介质模型模拟网衣,建立了模拟水流作用下平面网衣周围流场的三维数值模型。利用最小二乘法分析作用在平面网衣上的水流力与流速和冲角的关系,得到对应的多孔介质系数,使得多孔介质区域具有与网衣相同的阻水效果。运用该数值模型模拟了水流作用下平面网衣周围的流场,并与物理模型试验结果进行了比较。比较结果表明,不同流速和冲角条件下计算和试验获得的网衣周围流速值一致。证明了该数学模型对模拟网衣周围流场的适用性。     

两层黏性流体中直立圆柱体绕流的三维数值模拟

研究了两层流体中直立贯底圆柱体的三维黏性绕流问题.以不可压缩Navier-Stokes方程为控制方程,应用VOF方法追踪两层流体的内界面,建立了该问题的数值模拟方法.成功地数值模拟了两层流体中圆柱体黏性绕流产生的三维尾涡特征,表明了流体的密度分层效应对直立贯底圆柱体的尾涡特性和阻力系数都是有影响的.在海洋立管涡激振动的研究中,考虑流体的密度分层效应是重要的.     

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。     

计及自由面兴波和螺旋桨非定常旋转效应的集装箱船舶绕流场计算研究

该文以商用软件FLUENT为平台,以KCS算例为对象,进行了计及自由面和螺旋桨非定常旋转效应的计算。考察了时间步长、自由面是否固化、湍流模式和网格数量、计算策略对计算结果的影响,确定了工程适用的计算方法,并应用于9000TEU集装箱船舶,与试验结果比较,吻合良好。     

圆柱尾迹流场中横向振荡翼型绕流的数值模拟

该文数值模拟了静止圆柱尾迹中横向振荡翼型绕流的涡结构、力及频谱特性,揭示前方尾迹流场对振荡翼绕流特性的影响,以了解鱼类游动时自主利用前方流场有利干扰的流体力学机理。研究表明圆柱尾迹的影响可导致翼型前缘涡脱落模态发生变化;翼型尾迹的频谱特性更加复杂;在一定的参数下翼型阻力系数可以整体下降。     

The effect of free surface on cloud cavitating flow around a blunt body

In this study, the effect of the free surface on the cloud cavitating flow around a blunt body is investigated based on the water tank experiment and the CFD method. Numerical results are in good agreement with experimental data, and the mesh independence of the methods is verified. The cavity evolution process includes the cavity growth, the re-entrant jet, the cavity shedding, and the collapse, which can all be observed from the water tank experiment. The effects of the free surface on the cavity length, the thickness, and the cavity evolution period are analyzed by comparing the difference between the cavitating flows on the upper and lower sides of the body. This study also examines the effect of the distance between the free surface and the model through a series of water tank experiments and numerical simulations. The cavity stability and asymmetry, as well as the thickness and the velocity of the re-entrant jet inside the cavity, which varies with the submerged depth, are discussed with consideration of the effect of the free surface. The effect of the free surface on the cavitating flow around the blunt body is enhanced with the decrease of the submerged depth.     

三峡水轮机全流道三维流动数值模拟研究

本文使用商业CFD软件FLUENT,开发了部分接口程序,进行了全流道原型水轮机三维湍流数值模拟研究,计算对象是中国水利水电科学研究院机电研究所为三峡右岸开发的水轮机模型,该水力模型有完整的模型试验资料,可用于检验计算结果。水轮机全流道三维湍流数值模拟,计算区域为包括蜗壳、固定导叶、活动导叶、转轮和尾水管的全部流道。模拟中控制方程采用了三维时均N—S方程、湍流模型采用两方程RNG k-ε模型,数值方法采用贴体坐标的有限体积法。共进行了3个开度条件下的计算,每个开度各进行4个典型工况的三维湍流流场模拟,通过数值方法求解控制方程,获得了全流道的流速和压力分布。计算结果表明流速和压力分布合理,数值计算得到的效率与试验得到的效率进行比较,结果吻合良好。     

宽顶堰水流数值模拟分析

本文利用紊流模型模拟了带有曲线自由表面的宽顶堰流的紊流流场,采用VOF法来确定自由表面,采用气液两相流计算模型对宽顶堰流场进行了数值模拟,计算结果与试验数据较为吻合.模拟结果表明,数值模拟是作为研究水利工程中带有自由表面的水流结构的一个强有力的工具,其结果对物理试验也是一个很好的补充.     

丁坝群附近流场及局部冲刷的三维数值模拟

为探索丁坝群附近水流流场,揭示其局部冲刷的形成机理,该文采用Flow-3d软件,选取RNG k-ε湍流模型和以希尔兹(Shields)数为基础的泥沙推移质输沙率模型对上挑丁坝群的周围流场分布和局部冲刷进行了三维数值模拟。研究发现,丁坝群间涡系结构复杂,第一座丁坝坝头处有一对反向的旋涡和下潜水流,切应力达到最大值,使得该位置有较大冲刷坑发生,解释了冲刷机理。冲刷坑的模拟深度和范围与实验结果吻合较好,表明该模型可以用于丁坝群及相关河道整治工程的流场和冲刷坑计算。     

Verification and validation of URANS simulations of the turbulent cavitating flow around the hydrofoil

In this paper, we investigate the verification and validation(VV) procedures for the URANS simulations of the turbulent cavitating flow around a Clark-Y hydrofoil. The main focus is on the feasibility of various Richardson extrapolation-based uncertainty estimators in the cavitating flow simulation. The unsteady cavitating flow is simulated by a density corrected model(DCM) coupled with the Zwart cavitation model. The estimated uncertainty is used to evaluate the applicability of various uncertainty estimation methods for the cavitating flow simulation. It is shown that the preferred uncertainty estimators include the modified Factor of Safety(FS1), the Factor of Safety(FS) and the Grid Convergence Index(GCI). The distribution of the area without achieving the validation at the U v level shows a strong relationship with the cavitation. Further analysis indicates that the predicted velocity distributions, the transient cavitation patterns and the effects of the vortex stretching are highly influenced by the mesh resolution.     

台阶突扩三维粘性流动数值模拟

利用三维粘性流动数学模型，研究了台阶突扩流动的三维特性。不同的雷诺数Re情况下，计算所得的流态、流速和压力分布与B.F.Amarly等的试验和计算结果相吻合，表明所建立的三维粘性流动数学模型具有较强的模拟能力和较高的计算精度。