粘性流中的二维兴波水翼水动力特性研究

本文采用边界层的概念来研究粘性流中的二维兴波水翼之水动力特性的数值计算方法。考虑到边界层与外部势流的相互干扰，运用了势流与边界层的相互迭代计算，从而求得两者相互匹配的解。用势流解求得的水翼升力系数往往比实验值明显偏大。而用本文的方法，从算例来看，计算结果比势流解减小１５％左右，而与实验值比较接近。本文还讨论了兴波阻力的计算方法，并有算例。     

二维兴波水翼水动力预报的涡分布法

本文用奇点面分布法预报二维自由面边界下水翼的水动力特性。采用线性化的自由面边界条件。水翼表面划分为若干单元，每个单元上布置线性分布的涡，并在其中点满足Ｎｅｕｍａｎｎ型物面边界条件。与试验结果比较表明，计算结果是合理的，本计算方法能显示二维兴波水翼水动力特性与Ｆｒｏｕｄｅ数，相对浸深和攻角的关系。     

基于B样条网格的三维水翼水动力性能研究

该文应用低阶速度势面元法建立了预报三维水翼水动力性能的数值方法,重点对翼梢和尾涡进行了研究。文中采用基于B样条的网格划分方法,在水翼前缘处的弦向网格线与外轮廓线正交,在尾缘处与尾涡离开的速度方向相一致。翼梢上尾涡分离点的位置采用迭代的方法进行确定。对于三维升力问题而言,横向流动的影响作用很大,本文对现有的库塔条件形式进行了改进,在考虑横流影响的前提下,满足随边荷载为零的条件。通过对计算结果与试验结果进行比较表明,将基于B样条的网格划分方法及改进的库塔条件应用于已有的面元法程序中,能够很好地改善计算结果的精度。     

复合材料水翼水动力响应数值模拟研究

该文针对NACA0009复合材料梯形水翼进行流固耦合数值计算,研究复合材料水翼水力阻尼及水弹性响应特性。研究建立了复合材料水翼流场模型、结构模型、流固耦合计算模型及湿模态模型,并利用实验结果对模型进行验证。模态分析结果表明：复合材料铺层角φ影响水翼模态振型,相比于φ=0°铺层,φ=+30°铺层和φ=-30°铺层水翼的一阶模态频率降低,二阶和三阶模态频率升高。研究进一步对水翼振动过程的阻尼特性进行分析,得到了水力阻尼比与流速的经验关系式,复合材料水翼水力阻尼比与流速成正比,且相比于φ=0°铺层,φ=+30°铺层和φ=-30°铺层水翼的水力阻尼比更大。分析了不同流速下复合材料水翼的水动力载荷特性：对于稳态水动力载荷,φ=+30°铺层水翼的载荷系数随流速增加而增大,φ=-30°铺层随流速增加而减小,φ=0°铺层随流速增加而略有增加;对于瞬态水动力载荷,初步分析表明,水翼受到的水动力作用形式与铺层角相关：相较于流速,铺层角φ对瞬态载荷分布的影响更大,且φ=+30°铺层水翼吸力面尾缘附近所受水动力比φ=0°铺层更大。     

二维振荡超空化水翼水动力性能分析

该文以ys 930超空化水翼和NACA 65410水翼作为研究对象,采用RNG k-ε湍流模型、Zwart-Gerber-Belamri空化模型以及动网格技术,对比两种翼型在俯仰、升沉以及俯仰升沉复合运动情况下的水动力性能。结果表明:运动幅值的增加会使得升力系数和阻力系数曲线峰值明显提高;水翼在俯仰和复合运动情况下的升力系数和阻力系数会产生明显的尖峰,而尖峰主要是由下翼面气泡溃灭造成的。为进一步研究两种翼型的水动力性能,将升力系数和阻力系数的平均值和方差进行对比分析。结果表明:在升沉运动中,ys 930水翼的升阻力系数平均值始终高于NACA 65410水翼;但在俯仰和复合运动中,运动幅值的提高会使得NACN 65410水翼的升阻力系数平均值高于ys 930水翼;在三种运动模式下,ys 930水翼升阻力系数的方差较大,稳定性较低。从升阻比来看:ys930水翼在升沉运动中可以获得较高升阻比;但在复合运动情况下,随着俯仰角度的增加,NACA 65410的水动力性能明显提高。     

静水中摆推式水翼的水动力分析与实验研究

针对静水中作摆动推进的水翼,采用用非定常涡格法对其进行水动力分析,并进行了静水中的相关推进实验。在理论计算中作者提出了一种非线性尾涡面模型处理办法,并将这种尾涡面模型下的计算结果与试验结果进行了对比,对比表明在计算中采用这种非线性尾涡面效果理想。最后,针对提出的这种非线性尾涡模型处理方法展开了进一步的探讨,并按此计算了有来流工况下的尾涡面形状,给出了计算结果。     

仿生导管桨水动力性能研究

受座头鲸带有前缘凸起鳍的启发,该文将凹凸结节应用于桨叶导边,试图改善导管桨在小进速系数工况下的水动力和空泡性能。运用自编程序,以19A导管+Ka4-70螺旋桨作为原型桨,将导边进行内凹设计:通过改变特定位置剖面弦长,设计出带有凹凸形导边的仿生导管螺旋桨。运用商业CFD软件开展其水动力性能与流动的模拟与分析,建立仿生导管桨性能分析的CFD数值仿真预报方法。开展了导边凹凸结构的变参数计算研究,选择效率提高最多的仿生桨进行了流场分析。基于CFD计算结果,初步发现:①一定范围内导边凹凸结节的间隔步长越小,结节产生的效果越好,且根部结节效果比叶梢附近的结节效果要好。②凹谷处切面的桨叶推力会有所提高以补偿因桨叶表面积减少造成的推力损失。③单一形式的余弦函数曲线不能最大限度地提高桨叶性能,组合函数曲线节能效果最好。     

带附体的门桥水动力性能试验研究

为了改善门桥的水动力性能,增设了对近壁面流场进行流动控制的水翼.船模水池中的模型拖曳试验表明,尽管水翼会增加门桥的水阻力,但只要合理地设计水翼的翼型、攻角和安装位置,可以改善和提高门桥水动力性能.     

摆动叶片式波浪能发电装置的水动力性能分析

简述了摆动叶片式波浪能发电装置的结构和工作原理,结合波浪力学和浅水波理论对摆动叶片进行理论分析,推导出俘获效率公式。为了分析装置的性能,采用Fluent软件仿真的方法,分析了摆角和波高参数对装置的水动力学性能的影响,提出最佳摆角概念,并研究了最佳摆角与波高的关系。研究结果表明:装置的俘获效率随着摆角的增大先增大后减小;随着波高的增加,装置的俘获效率在增加,研究结果为后期装置的试验提供了理论依据。     

仿生机器鱼尾鳍推进性能实验研究

该文研制了仿鲤鱼机器鱼平台,并通过系泊测力实验研究了自然界常见的圆形、叉形和新月形尾鳍的推进性能,同时比较了刚性、弹性两种材质对尾鳍推进性能的影响。结果表明,弹性尾鳍让机器鱼的平均推力随振幅和频率的变化更平稳;在摆动频率处于中高段时,展弦比较大的刚性尾鳍比弹性尾鳍能产生更大的推力,而展弦比较小的弹性尾鳍比刚性尾鳍能产生更大的推力。     

Hydrodynamics of a flapping foil in the wake of a D-section cylinder

The water environment of swimming fish in nature is always complex which includes various vortices and fluctuations.In order to study the interaction between the fish and its surrounding complex flow, the physical model with a D-section cylinder placed at the front of a flapping foil is employed.The D-section cylinder is used to produce vortices to contact with the foil as well as the vortices shed from the foil.According to the experimental work of Gopalkrishnan et al., there are three interaction modes between vortices shed from the cylinder and the flapping foil,which are expanding wake, destructive interaction and constructive interaction.Here in this article,three of those typical cases are picked up to reproduce the vortices interaction modes with the modified immersed boundary methods and their hydrodynamic performances are studied further.Results show that, for expanding wake mode and destructive interaction mode, the incoming vortices contact with the foil strongly, inducing relative low pressure domains at the leading-edge of the foil and enlarging the thrust of foils.For constructive mode, the foil slalom between the shed vortices from the D-section cylinder do not contact with them obviously and the foil’s thrust is only enlarged a little.     

Numerical and experimental studies of hydrodynamics of flapping foils

The flapping foil based on bionics is a sort of simplified models which imitate the motion of wings or fins of fish or birds. In this paper, a universal kinematic model with three degrees of freedom is adopted and the motion parallel to the flow direction is considered. The force coefficients, the torque coefficient, and the flow field characteristics are extracted and analyzed. Then the propulsive efficiency is calculated. The influence of the motion parameters on the hydrodynamic performance of the bionic foil is studied. The results show that the motion parameters play important roles in the hydrodynamic performance of the flapping foil. To validate the reliability of the numerical method used in this paper, an experiment platform is designed and verification experiments are carried out. Through the comparison, it is found that the numerical results compare well with the experimental results, to show that the adopted numerical method is reliable. The results of this paper provide a theoretical reference for the design of underwater vehicles based on the flapping propulsion.     

Hydrodynamic performance of distributed pump-jet propulsion system for underwater vehicle

A type of distributed pump-jet propulsion system （DPJP） is developed with two or four specially designed pump-jet pods located around the axisymmetric underwater vehicle body symmetrically. The flow field is numerically simulated by solving the RANS equations with the finite volume method. The computational method is validated by comparing the calculated hull resistances of the SUBOFF AFF-3 model and the open water performance of a ducted propeller with experimental data. The hydrodynamic performances of the DPJP with different axial or radial positions and numbers of pump-jet pods are obtained to analyze the interactions between the hull and the pump-jet pods. It is shown in the calculated results that the decrease of the distance between the pods and the hull leads to an increase both in the efficiency of the pods and the thrust deduction factor due to the effect of the stern wake. And, a negative thrust deduction factor can be obtained by locating the DPJP at the parallel middle body near the aftbody of the vehicle to improve the hydrodynamic performance of the DPJP. Besides, the increase of the number of pods will cause a remarkable decrease of the total propulsive efficiency of the DPJP with the pods mounted on the stern planes, while a small decline of the total propulsive efficiency of the DPJP is observed with the pods mounted on the parallel middle body.     

静水中长鳍扭波推进的水动力数值研究

长鳍扭波推进是一种典型的鱼类游动方式,具有高效、低噪、机动灵活等一系列优点。该文以"尼罗河魔鬼"鱼为仿生研究对象,采用弹性光顺法和局部网格重划法的动网格技术对大摆幅的长鳍扭波推进运动流场进行了数值计算研究,鳍条最大摆幅高达85°,对长鳍扭波推进在系泊状态下的水动力进行了研究,并与试验结果进行了比较验证。数值分析了鳍面压力分布及其随相位的变化,以及与推力产生的关联,并分析了长鳍扭波推力随扭波频率的变化,研究表明,系泊状态下,推力系数不随频率而改变。     

Hydrodynamic performance of a vertical-axis tidal-current turbine with different preset angles of attack

The instantaneous angle of attack on the blade has a significant effect on the hydrodynamic performance of a vertical-axis tidal-current turbine with straight blades. This paper investigates the influence of different preset angles of attack on the hydro-dynamic performance of a three-bladed, vertical-axis, tidal-current turbine both experimentally and numerically. Experiments are carried out in a towing tank. This tested turbine’s solidity is 0.1146. The preset angles of attack on the blade are -3°, 0° , 3° , and 5°, in the experiments. Experimental results show that with the increase of the preset angle of attack from -3°, to 5° , the hydrodynamic performance of the turbine is improved significantly with the power coefficients being increased from 15.3% to 34.8%, respectively. Compared to the result of a 0° preset angle of attack, the performance of the turbine with positive preset angles of attack is experimentally demonstrated to be beneficial. This performance improvement is also shown by numerical     

不同流速对鲫鱼推进效率影响的数值研究

鱼类趋流性的试验和鱼类游动的数值模拟是当前研究的两个热点,大多数鱼类不仅有趋流特性而且还能高效节能的向前推进,开展鱼类趋流性与推进效率关系的研究既能完善鱼类推进机理理论,也能在鱼道设计时提高其过鱼效率。本文以鲫鱼在不同恒定流速中的实测游泳数据为依据,利用计算流体力学软件flow-3d对鱼类波状摆动进行数值模拟,建立鲫鱼游动的数值计算模型,研究在不同流速下鲫鱼完成一个运动周期后所对应的推进效率。结果表明,随着流速的增大鱼的推进效率呈现出先增大后减小的变化趋势,当流速条件为0.5 m/s时对应的鱼类推进效率值最大,也是推进效率随流速变化的转折点。该研究获得了鲫鱼在顶流运动状态下鱼类推进效率与流速条件之间的相关关系。     

热污染的一、二维耦合模型及其应用

滨海、河口二个火电站并存时，其冷却水所释放的热量常造成周围水体的温度上升并相互干扰、叠加。它们之间的水体、温度相互流动、渗混，交接点上的水位、流速及温升同时满足一、二维方程，为此必须进行耦合解。本文提供了一、二维任意交角普遍性的耦合解法，并应用北仑、镇沦二个火电站之间的热污染计算为实例，求得了它们相互影响的定量值。     

洞庭湖洪水空间分布和运动特征分析

 鉴于目前仍缺少有关洪水涨落在湖泊中空间分布及其演进的运动特征研究,以1998年洞庭湖洪水事件为例,运用洞庭湖地区水系水动力学模型模拟成果,细致地分析了洞庭湖三大主要湖区的洪水分布形态和运动特征,并对江湖窜流形成进行了初步分析。模拟成果表明：洞庭湖具有“低水河相、高水湖相”的特征;其东、南两个湖区在高洪水位时期湖相特征突出,湖区流向单一,流速不大于0.2 m/s;西洞庭湖区由于各股水流交汇、不同的洪水组合以及出口的制约,致使湖区产生流态复杂、流向不一以及洪峰叠加等现象。       

海流能转换器叶片翼型的失速和水动力特性的数值研究

海流能转换器叶片翼型的水动力学性能优劣是海流能开发利用的关键因素.该文基于浙江工业大学水力学实验室设计的海流能转换器叶片,利用商川CFD模拟软件FLUENT对其叶片翼型在来流攻角从-4°～20°情形下的水动力特性进行了相应的数值模拟计算,得到翼型周围流场的速度分布、压力分布、翼型的失速特性以及水动力特性与攻角α的关系,可供设计高效的海流能转换器叶片时参考.