三鱼群游流动干扰及其减阻机理的数值研究

观察研究发现,在鱼类的群游中,鱼体可以有效利用相互之间有益的干扰,减少游动阻力,增强自己的推力和游动效率。文中作者基于以往建立的动态混合网格生成方法以及不可压缩流非定常计算方法,对三鱼呈“三角”阵型排列的群游进行了数值模拟,通过对不同横向间距、不同流向间距、不同相位差等游动状态下的流场结构、力学特性的比较,分析了鱼体之间的横向干扰和流向干扰,研究了流动干扰减阻的机理。     

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。     

鳞鲀模式推进机理的数值研究

通过求解三维非定常不可压缩N-S方程对鳞鲀模式的游动进行了数值模拟,研究了鳞鲀模式游动的水动力学特性与流场特征,揭示鳞鲀模式游动的推进机理。结果表明,鳞鲀的背/臀鳍在一个波动周期内脱出两个非对称涡环,涡环中心诱导射流为鳞鲀提供推力;鳞鲀的推力分别依靠鳍面的波动和横侧摆动产生,背/臀鳍的安装角度使鳞鲀能更有效地利用这两部分的推力分量,且平衡沉浮力分量。鳞鲀所受推力随波动频率和幅度的增大而增大,随波长的增大先增大后减小,并且波长过大时,推进效率会急剧降低。相比于身体-尾鳍摆动(BCF)推进,鳞鲀模式具有极高的推进效率。与长鳍扭波推进模式相比,鳞鲀模式则具有更强的机动性。     

金枪鱼自主波动游动的数值模拟

鱼类游动问题蕴含着复杂的流体力学机理,其仿生问题同时又有着重要应用背景.该文运用人工伪压缩方法求解三维不可压缩非定常Navier-Stokes方程,计算分析金枪鱼从静止加速起动到巡游直至减速波动游动的全过程,得到鱼类游动时各状态的流场信息以及受力情况.同时结合计算结果,对鱼类游动过程进行了参数研究并且分析了鱼体推力产生的机理.计算结果分析表明:数值求解非定常Navier-Stokes方程能够模拟鱼体运动时的流场;鱼体摆动频率以及摆幅会影响鱼的游动;持续摆动产生的涡环形成反卡门涡街是鱼体游动时产生推力的重要因素.     

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。     

鱼类鳗鲡模式推进的游动性能分析

本文对水生动物最基本的游动方式波状摆动,即典型的鳗鲡模式游动,从流体动力学角度进行了分析。主要讨论游动的推进性能。文中采用势流理论中的涡环法,计算了各种展弦比《背腹轴与体长之比)的三维柔板作常幅行波状摆动时产生的推力、维持运动所需要的能量以及推进的流体力学效率等力能量,得到了它们随各种运动参数的变化关系。进而分析了这种游动方式的推进性能,并可定性地解释一些真实鱼类的游动现象。     

喷水推进船负推力减额机理研究

对喷水推进与船体相互作用研究中发现的中高航速推力减额为负值的机理作出了解释.通过求解雷诺时均方程,考虑船体纵倾与吃水变化,以CFD边界条件模拟喷水推进泵吸水与射流作用,数值计算了喷水推进船模自航条件下的流场.着重研究喷水推进改变船后流动状态与船体航态对推力减额的影响.结果表明,与螺旋桨船显著不同的是,喷水推进器向船后空气中喷水,喷射水流不加速船艉流场,喷水推进进流只在低航速加速船艉流场,船体压阻力增加是低航速推力减额为正的主要原因.中高航速喷水推进吸水破坏船底边界层,船体黏性阻力降低是推力减额为负值的主要原因.作用于进水流道的力及产生的埋艏力矩有减小船体吃水与纵倾的趋势,该趋势在高航速更加明显,本文研究结果表明升力与埋艏力矩作用并非推力减额为负的主要原因.     

反拱透水底板拱端推力与板块位移研究

本文基于模型试验并结合数值模拟研究了反拱透水底板的拱端推力与板块位移特性。结果表明,与不透水底板相比,透水底板可以显著的减小拱端推力,并且拱端推力与板块位移均随开孔率的增加而减小,从而可以提高反拱底板的稳定性。结合拱端推力的频谱分析可知,开孔后拱端推力的脉动能量降低,并且功率谱重心向低频移动。     

基于摆频控制的鱼群自主游动数值模拟研究

本文提出了一种通过控制仿生鱼摆频来达到自主推进状态的数值模拟新方法(简称摆频控制法),并利用自主游动速度与摆频之间的近似关系以及牛顿第二定律推导出了摆频的控制方程.通过与传统的速度控制法(仿生鱼的自主游动速度由牛顿第二定律确定)的比较,验证了该方法的可靠性,并对影响该方法收敛速度的敏感因子进行了讨论,给出了最优参数,并通过模拟三条仿生鱼组成的鱼群基本单位在Re=5000时的自主游动,证明了摆频控制方法在鱼群自主游动数值模拟中的有效性.结果表明,鱼群整体平均节能约19％,推进效率平均提高了约36％.     

长鳍波动推进水动力效率计算分析

"尼罗河魔鬼"鱼在保持身体不变形的情况下依靠其长背鳍波动推进实现直线巡游,通过改变波动传播方向,即可实现前进或后退。鉴于其独特的优点,长鳍波动推进成为仿生推进研究重要的推进模式之一。目前对这种仿生推进模式的水动力学研究还相对较少,已有的一些研究工作中相当一部分还不涉及推进效率。该文通过数值计算,对柔性长鳍波动推进的水动力和推进效率进行研究。该研究对于长鳍沿轴向各部分鳍面的输入功率的要求及其对总推力的贡献分析具有参考价值。     

HYDRODYNAMIC ANALYSIS AND SIMULATION OF A SWIMMING BIONIC ROBOT TUNA

A dynamic model for undulatory locomotion was proposed to study the swimming mechanism of a developed bionic robot tuna. On the basis of inviscid hydrodynamics and rigid-body dynamics, the momentum and propulsive force required for propelling the swimming robot tuna’s flexible body was calculated. By solving the established dynamic equations and efficiency formula, the swimming velocity and propulsive efficiency of the bionic robot tuna were obtained. The relationship between the kinematic parameters of the robot tuna’s body curve and the hydrodynamic performances was established and discussed after hydrodynamic simulations. The results presented in this article can be used to increase the swimming speed, propulsive thrust, and the efficiency of underwater vehicles effectively.     

两种手姿态在不同攻角下划水的数值模拟

该文旨在用计算流体力学（CFD）的方法研究游泳推进问题,建立了手掌和前臂的联接模型,并生成3D非结构网格，计算了两种不同手姿态：并拢和张开在不同来流速度和攻角下的推进阻力和推进升力，并结合计算结果进行了流场分析，研究了两种手姿态对推进效率的影响。结果表明，在各个攻角状态下，手并拢划水均能获得更高的推进效率。     

NUMERICAL STUDY ON PROPULSIVE PERFORMANCE OF FISH-LIKE SWIMMING FOILS

1. INTRODUCTION The study of the movement of fishes can be very informative in exploring mechanisms of unsteady flow control because movements in fish is a result of many millions of years of evolutionary optimization. Previous studies have shed light on …     

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.     

DYNAMICS OF FREE STRAIGHT SWIMMING OF ANGULLA ANGULLA INCLUDING FORWARD, BRAKING AND BACKWARD LOCOMOTION

Eels can swim backward by reversing the direction of the traveling wave along the body. The propulsive mechanism of an eel, angulla angulla, during its self-propelled straight swimming, including forward swimming, braking and switching direction to backward swimming was numerically studied. The problem was reasonably simplified to a loose-coupling problem of fish swimming dynamics and hydrodynamics only in the swimming direction. The approach involved the simulation of the flow by solving the two-dimensional unsteady incompressible N-S equations and the fish motion dynamic problem with Newton’s second law. Visualizations of flow fields and vortex structures were performed. The propulsive mechanism and dynamics during each process were investigated and the effects of controllable factors on forward free swimming were discussed.     

大坝泄水对鱼类洄游能力的影响研究

大坝的建设将天然河道分隔成上、下两个环境单元,改变了河道的流量、流速和水位等水文要素,使原有的水力条件及生态环境都发生了变化,对鱼类的洄游、繁殖和生长等都产生较大影响。以江河湖泊常见鱼种—成年鲤为研究对象,以0.02 m~3/s为基础流量,按照0.01 m~3/s的流量递增进行大坝泄水模拟实验;采用声学信号监测技术监测成年鲤在不同泄水量下的洄游能力及游泳轨迹,分析不同泄水量的河道流场并与鱼类游泳轨迹进行拟合,研究不同流速对鱼类洄游能力的影响。结果表明:成年鲤的洄游距离、游泳速度随着河道流速增大而逐渐减小,成年鲤洄游开始出现困难、开始出现逆流后退以及无法洄游时河道流速分别为0.42,0.48 m/s和0.62 m/s;泄水量每增加一个0.01 m~3/s流量梯度,成年鲤洄游距离约减少1.5 m,说明随着河道流速增大鱼类洄游轨迹变化是一个逐渐收敛的过程。大坝泄水过程同时还会造成氮气和氧气过饱和、改变水体温度和浊度从而对鱼类生存环境、繁殖及鱼类资源造成影响。     

异齿裂腹鱼通过鱼道内流速障碍能力及行为

鱼类通过流速障碍能力是鱼道设计的主要生态指标,目前国内外主要使用封闭游泳水槽进行鱼类各种游泳速度指标及游泳行为研究,其水流流态及鱼类游泳行为与鱼类通过鱼道的实际状态有较大的差距,有必要结合鱼类游泳速度指标来探索能够更加准确量化鱼类通过鱼道流场的游泳能力测试方法。首先,在封闭游泳水槽中通过速度递增法测得异齿裂腹鱼临界游泳速度(101.01±20.86 cm/s)和突进游泳速度(196.94±21.80 cm/s);然后,以临界游泳速度和藏木水电站鱼道竖缝流速(110.00 cm/s)为参考,通过在开放游泳水槽内加不同束窄梯形体,形成类竖缝式鱼道的鱼类自主游泳能力测试水槽,开展两种底坡条件下4级短竖缝(工况1和工况2竖缝流速为101.55±14.87 cm/s、114.63±24.28 cm/s,竖缝顺水流长度均为40 cm)和单级长竖缝(工况3竖缝流速为137.45±17.63 cm/s、竖缝顺水流长度为160 cm)下试验鱼通过流速障碍能力和行为研究。试验结果表明:工况1、工况2下试验鱼通过4级竖缝成功率分别为82.05%、84.62%,通过流速大于临界游泳速度的竖缝时,持续爆发游泳时间为0.52±0.34 s;工况3下93.33%试验鱼以209.43±21.76 cm/s游泳速度成功通过单级长竖缝;3种工况下试验鱼通过流速大于临界游泳速度的竖缝时,以与突进游泳速度无显著性差异(P0.05)的恒定游泳速度(214.01±30.64 cm/s)上溯。鱼类游泳轨迹与流场耦合分析表明:鱼类上溯所需时间及路径长度与其选择的游泳路径密切相关,试验鱼通过借助回流区同向水流推动,增加上溯效率。本文研究方法及研究结论可为鱼道设计、改造、评价提供依据。     

ANALYSIS OF HYDRODYNAMICS FOR TWO-DIMENSIONAL FLOW AROUND WAVING PLATES

Hydrodynamic characteristics for two-dimensional flow around a waving plate are investigated. Under large Reynolds number approximation, the flow is assumed to be a combination of the outer potential flow and a thin vortex layer, which consists of a boundary layer and a shed free shear layer. A nonlinear mathematical formulation for describing the outer unsteady potential flow coupled with an unsteady boundary layer equation for the inner viscous flow adjacent to the waving plate is developed. A semi-analytical method with a nonlinear Kutta condition imposed at the trailing edge is used to solve the velocity field of the outer flow and the evolution of wake vortex induced by a large-amplitude waving plate. The unsteady boundary layer equation is solved by extending Pohlhausen’s method to its unsteady counterpart. The thrust and viscous drag coefficients, propulsive efficiency, and the pattern of wake vortex sheet are discussed.     

Propulsive performance of a passively flapping plate in a uniform flow

Propulsive performance of a passively flapping plate in a uniform viscous flow has been studied numerically by means of a multiblock lattice Boltzmann method. The passively flapping plate is modeled by a rigid plate with a torsion spring acting about the pivot at the leading-edge of the plate, which is called a lumped-torsional-flexibility model. When the leading-edge is forced to take a vertical oscillation, the plate pitches passively due to the fluid-plate interaction. Based on our numerical simulations, various fundamental mechanisms dictating the propulsive performance, including the forces on the plate, power consumption, propulsive efficiency and vortical structures, have been studied. It is found that the torsional flexibility of the passively pitching plate can improve the propulsive performance. The results obtained in this study provide some physical insights into the understanding of the propulsive behaviors of swimming and flying animals.