均匀流中横向振荡圆柱绕流场的数值分析

针对工程中关心的振荡圆柱绕流问题,采用同位网格系统中的SIMPLE算法求解N-S方程,以及动网格技术模拟圆柱的运动边界。对均匀来流中的横向振荡圆柱绕流场进行数值模拟,计算了振荡圆柱升力系数、阻力系数随时间的变化曲线,以及不同相位时的流线矢量图和涡量等值线分布图。为验证模型的可靠性,对静水中的振荡圆柱流场进行模拟。与实验及数值计算结果吻合较好。     

某二维水翼空化数值模型对比

以二维水翼计算模型为研究对象,采用数值模拟的方法,通过不同的空化模型和湍流模型对计算模型进行数值模拟研究,得到了翼型在空化过程中空泡的运动规律。结果表明:该翼型在不同空化模型下,发生空化时,空化过程包含了空泡的产生、发展、脱落和溃灭几个过程,空化的运动过程总具有明显的周期性;Schnerr-Sauer模型的计算结果与实际的水翼空化流动过程相吻合,Schnerr-Sauer空化模型可以很好地模拟绕水翼的空化流动过程。     

某二维水翼空化数值模型对比研究

以二维水翼计算模型为研究对象,采用数值模拟的方法,通过不同的空化模型和湍流模型对计算模型进行数值模拟研究,得到了翼型在空化过程中空泡的运动规律。结果表明:该翼型在不同空化模型下,发生空化时,空化过程包含了空泡的产生、发展、脱落和溃灭几个过程,空化的运动过程总具有明显的周期性;Schnerr-Sauer模型的计算结果与实际的水翼空化流动过程相吻合,Schnerr-Sauer空化模型可以很好地模拟绕水翼的空化流动过程。     

方柱绕流CFX三维数值模拟

该文利用计算流体力学软件CFX,对恒定来流条件下黏性不可压缩流体的圆柱和方柱绕流进行了数值模拟。采用有限体积法和SIMPLE计算方法,求解不可压缩Navier-Stokes方程。首先开展雷诺数(Re)等于100和300时的圆柱和方柱绕流问题的二维数值模拟,分析比较了网格大小和时间步长对模拟结果的影响,并比较了不同柱体情况下的流体流动的差异性。进而对Re=100、300时方柱绕流问题进行了三维数值模拟,重点分析了各截面上阻力和升力系数、Strouhal数以及涡量特性与二维结果的差异。发现Re=300时,周向压力、速度场和涡量场与Re=100时相比存在明显的三维特性,并且由于二维流动结构发展成三维流动结构时需要消耗能量,导致三维的阻力升力系数计算结果均小于二维计算结果。研究表明,该文的数值结果与文献结果吻合良好。     

二维浅水方程的高阶松弛格式求解

利用松弛方法，将二维浅水方程转化为松弛方程组，并用逐维五阶WENO重构和显隐式Runge-Kutta方法对松弛方程组的空间和时间方向进行离散，建立了求解二维浅水方程的五阶松弛格式。WENO重构方法的引入既提高了格式的精度，又可保证格式是无振荡的。应用该格式对圆柱溃坝等问题进行了数值模拟，计算结果与用其它方法所得结果吻合，表明了方法的有效性。     

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。     

近地面翼型气动特性的实验测量和数值模拟

该文研究了二维翼型地面效应的气动特性问题。首先在风洞中对NACA0012翼型进行了水平光滑壁面附近的测压实验,得到了低速条件下该翼型的表面压力分布实验数据。而后利用数值模拟方法,计算了采用定常不可压缩流动N-S方程和标准S-A湍流模型的翼型地面效应。经对比分析,计算结果与风洞实验数据在相同实验条件下较为一致,验证了该数值方法的可靠性。进而通过对NACA0012翼型在运动地面和固定地面两种不同的边界条件附近的绕流计算,给出了近地面飞行翼型气动性能随离地高度、攻角的变化规律。     

流向振荡圆柱绕流中的涡脱落模态分析

本文用有限体积法对平行于均匀来流方向受迫振荡的圆柱绕流问题进行了二维数值模拟。雷诺数选取Re=200、855等几种亚临界雷诺数情况。研究了不同振幅和振动频率下的流场结构、涡脱落模态和一些重要流动参数如升阻力系数、Strouhal数的变化关系。西文计算表明，流向振荡圆柱绕流中涡脱落方式可划分为对称与反对称两种形态，在反对称的涡脱落现象中又观察到了三种基本模态，相互竞争的各种模态间的共同作用对流动特征起决定性作用。同时计算结果还验证了在圆柱绕流实验中观察到的频率锁定现象。     

多向聚焦波浪作用下直立圆柱受力的实验研究

利用波能聚焦的方法在水池中模拟产生多向聚焦波浪,研究了多向极限大波作用在垂直圆柱上引起的波浪力的特点。实验中研究了不同的波浪参数,如聚焦波幅、谱峰频率、频率宽度和方向分布等多向聚焦波浪对圆柱作用的影响,并将实验结果与二维实验结果进行了比较。结果表明聚焦波浪参数对圆柱作用力具有明显的影响,并且实验结果与二维规则波结果相当,但比二维聚焦波浪实验结果要小。     

高雷诺数下圆柱绕流与大振幅比受迫振动的数值模拟

利用CFD方法,研究较高雷诺数下圆柱绕流及圆柱大振幅比横向受迫振动特性。在Navier-Stokes方程和k??湍流模型的基础上,对圆柱绕流分别进行了二维与三维的数值模拟,得到了圆柱绕流的升力系数和漩涡发放频率数等结果。研究结果表明,三维模拟的升力系数均小于二维模拟结果。利用Fluent的动网格技术进行大振幅比圆柱横向受迫振动的研究,得到圆柱在不同振动频率时的升力系数及漩涡发放规律和圆柱在特定振幅及频率下的"锁定"区间。     

The mechanism of flapping propulsion of an underwater glider

To develop a bionic maneuverable propulsion system to be applied in a small underwater vehicle, a new conceptual design of the bionic propulsion is applied to the traditional underwater glider. The numerical simulation focuses on the autonomous underwater glider(AUG)'s flapping propulsion at Re= 200 by solving the incompressible viscous Navier-Stokes equations coupled with the immersed boundary method. The systematic analysis of the effect of different motion parameters on the propulsive efficiency of the AUG is carried out, including the hydrofoil's heaving amplitude, the pitching amplitude, the phase lag between heaving and pitching and the flapping frequency. The results obtained in this study can provide some physical insights into the propulsive mechanisms in the flapping-based locomotion.     

潜体在两层海内波中的波浪力计算

本文以近似潜艇的细长回转体为模型，在两层海模式中三种不同潜深下，利用边界元法计算了内波对潜体的一阶垂荡波浪力和一阶纵摇波浪力矩，作为特例计算了近水面潜体的波浪力及力矩，并与实验结果进行了比较，两者吻合较好。     

EXPERIMENTAL STUDY OF VENTILATED SUPERCAVITIES WITH A DYNAMIC PITCHING MODEL

An investigation of the ventilated supercavitation for a supercavitating vehicle pitching up and down in the supercavity was carded out in a high-speed water tunnel. The emphasis is laid on the understanding of the interaction of the vehicle aft body with the cavity boundary. The flow characteristics were measured and the stability of supercaviting flow with different pitching frequencies and amplitudes was analyzed. In particular, the objectives of this study are to understand the effect of the impact upon the cavity distortion, and to quantify the impact process by investigating the evolution of the pressure inside the cavity and then the loads on the vehicle during the pitching motion. It is also shown that the evolution of the pressure detected in different,as inside the supercavity, is coherent and uniform during the periods of the pitching motion. This study is of direct relevance to reliable and accurate prediction of hydrodynamic loads associated with the slamming and impact on supercavitating vehicles.     

Numerical studies of the hysteresis in locomotion of a passively pitching foil

The direct-forcing fictitious domain method is extended to simulate the locomotion of a passively pitching foil. Our study focuses on the hysteresis phenomenon that the critical frequency for the reverse of the locomotion direction of the wing in case of decreasing frequency is smaller than that in case of increasing frequency. In our simulations, the hysteresis phenomenon is produced by imposing different initial conditions at a same frequency. Our results indicate that the ratio of the heaving amplitudes of two foil edges is crucial to the direction of the foil's horizontal motion, and the amplitude of the leading edge is generally smaller. The critical frequencies for the reverse of the locomotion direction are increased, when the foil-fluid density ratio is decreased or the spring constant is increased. The critical frequencies in the bi-stability regime also depend on the initial velocity imposed, and the hysteresis loop generally becomes larger if the initial velocities are closer to the terminal locomotion velocities of the foil.     

基于MPS方法数值模拟三维LNG液舱的晃荡问题

该文基于自主开发的无网格粒子方法求解器MLParticle-SJTU,将MPS方法(moving particle semi-implicit)应用到三维LNG液舱的晃荡问题中,分别研究了LNG液舱在单自由度纵摇和横摇激励下,装载高度和激励频率对液舱晃荡作用的影响。首先,对装载高度为70%H的LNG液舱在单自由度纵摇和横摇激励下的晃荡问题分别进行了数值模拟,并将计算结果与实验结果进行比较,验证了MPS方法的可靠性。其次,对比不同装载高度,不同激励频率下液舱晃荡的拍击压力和流场分布情况,分析了装载高度和激励频率对晃荡作用的影响,并分析了一阶固有频率和共振频率随装载高度的变化规律。数值结果表明:激励频率对晃荡幅度影响较大;当激励频率在一阶固有频率附近时,会发生剧烈的晃荡现象;52.5%H为危险装载高度,在共振频率下,产生的拍击压力最大。     

三体船在斜浪规则波中运动响应预报方法研究

对于三体船在波浪中的水动力预报,航速效应和主体与片体间水动力干扰效应是水动力载荷合理预报的关键之处,需合理考虑.二维半势流理论可较为准确反映上述效应,已在三体船顶浪中垂向运动响应理论预报上获得了较为满意的结果.在此基础上,该文探讨了该方法在三体船斜浪中运动特别是横摇预报上的应用.为较准确获得三体船横摇运动时粘性阻尼贡献,采用三体船模静水中自由横摇衰减试验获得了自由横摇运动衰减曲线,并经能量法处理获得了船舶横摇阻尼系数.然后,结合二维半理论,获得了三体船运动数值解.数值解与斜浪规则波中运动响应模型试验结果符合较好,反映本文所采用的数值方法可较好地预测三体船斜浪中水动力载荷和运动,可用于三体船在波浪中耐波性评估.     

NUMERICAL PREDICTION OF SUBMARINE HYDRODYNAMIC COEFFICIENTS USING CFD SIMULATION

The submarine Hydrodynamic coefficients are predicted by numerical simulations.Steady and unsteady Reynolds Averaged Navier-Stokes(RANS) simulations are carried out to numerically simulate the oblique towing experiment and the Planar Motion Mechanism(PMM) experiment performed on the SUBOFF submarine model.The dynamic mesh method is adopted to simulate the maneuvering motions of pure heaving,pure swaying,pure pitching and pure yawing.The hydrodynamic forces and moments acting on the maneuvering submarine are obtained.Consequently,by analyzing these results,the hydrodynamic coefficients of the submarine maneuvering motions can be determined.The computational results are verified by comparison with experimental data,which show that this method can be used to estimate the hydrodynamic derivatives of a fully appended submarine.     

NUMERICAL STUDY OF THE PITCHING MOTIONS OF SUPERCAVITA-TING VEHICLES

The pitching motions of supercavitating vehicles could not be avoided due to the lost water buoyancy.In order to have some insight for the design of the supercavitating vehicles,the fixed frequency and free pitching motions are investigated.A numerical predicting method based on the relative motion principle and the non-inertia coordinate system is proposed to simulate the free pitching motions of supercavitating vehicles in the longitudinal plane.Homogeneous and two fluid multiphase models are used to predict the natural and the ventilated supercavitating flows.In the fixed frequency pitching motions,a variety of working conditions are considered,including the pitching angular velocities and the supercavity scales and the results are found to be consistent with the available experimental results in literature.The mesh deformation technology controlled by the moment of momentum equation is adopted to study the free pitching motions and finally to obtain the planing states proposed by Savchenko.The numerical method is validated for predicting the pitching motions of supercavitating vehicles and is found to enjoy better calculation efficiency as comparing with the mesh regeneration technology.     

STUDIES ON THE NUMERICAl SIMULATION OF UNSTEADY FLOWS

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