桨-舵间距和雷诺数对潜艇尾部伴流场均匀性的影响研究

采用Realized k-ε湍流模型求解Reynolds平均Navier-Stokes方程,对SUBOFF全附体模型在低雷诺数和高雷诺数条件下的三维粘性流场分别进行了数值模拟,研究了桨-舵间距以及雷诺数对螺旋桨盘面伴流场的影响.计算结果表明:适当的加大桨-舵间距对提高潜艇尾流场的均匀性有显著的效果;桨-舵间距对潜艇桨盘面伴流场均匀性的影响在潜艇的低雷诺数状态和高雷诺数状态具有同样的规律.     

螺旋桨梢涡不稳定性机理与演化模型研究

螺旋桨尾流场的涡流特性是一个基础但又十分复杂的流体力学问题, 它的复杂性源于其蕴含复杂的漩涡系统, 且该漩涡系统会在高速的剪切层流动中不断演化, 其流体动力学行为, 如由稳定态演变为不稳定态的机理以及复杂工况环境中的流动现象, 一直是流体力学领域的难点和备受关注的热点问题. 从工程应用的角度看, 桨后梢涡的演化特性与船舶结构物的宏观特性直接相关, 更好地理解多工况下螺旋桨尾流的动力学特性, 将有助于改善与振动、噪声以及结构问题等相关的推进器性能, 对综合性能优良的下一代螺旋桨的设计和优化有着重要的现实意义. 本文基于延迟分离涡模拟、大涡模拟和无湍流模型模拟方法以及粒子图像测速流场测试分别开展了螺旋桨尾流动力学特性的数值与试验研究, 对螺旋桨尾流不稳定性的触发机理进行了揭示. 基于均匀来流中螺旋桨梢涡的演化机理, 提出了螺旋桨梢涡演化模型. 该模型能够较为准确地模拟螺旋桨梢涡的演化过程, 预测螺旋桨梢涡融合的时间和位置, 对螺旋桨流噪声预报和控制以及性能优良的螺旋桨设计具有重要意义.      

舵布置位置对船舶操纵性影响试验研究

舵合理布置于船尾螺旋桨后方能有效吸收螺旋桨尾流,达到船舶操纵性能优化设计的目的. 根据螺旋桨尾流特征,设计了舵的4个横向和3个纵向,共计6个舵布置位置方案,通过自由自航模型试验考察舵布置位置对操纵性的影响. 在湖上开展了船模回转、Z形操舵和回舵试验,速降和静横倾角的试验结果符合一般操纵性规律,表明试验结果的有效性.     

高速列车近尾流区湍流涡旋的数值计算及动力学讨论

主要针对缩尺比例1:30的高速动车组空气动力学模型的近尾流区域流场进行数值模拟,分析讨论了湍动能和湍流能量的产生,得到以下结论:对应于各展向位置的湍动能沿流向的变化规律与近尾流区涡旋结构携带能量的展向外移现象有关;在尾车鼻端附近,湍流涡旋具有显著的湍动能,并且各方向上的能量分量具有相同的量级,反映出湍流涡旋是高度三维的流动结构;靠近尾车鼻端的近尾流区湍流涡旋具有较强的从平均流动中提取能量的能力,并且结果表明,来自于车体底面和侧面的剪切流动沿垂向分别在一定空间范围内发挥重要的影响作用;大涡特征尺度沿流向增大,其中较小的涡旋对湍流能量的产生有主要贡献,同时,由于受到列车侧面较厚剪切层的影响,对湍流能量有贡献的涡旋所对应的积分尺度范围增大,从而使位于尾车鼻端附近的涡流能够在更大的流向范围内获取用于维持湍流尾流的能量.     

配重位置对全动舵面颤振抑制效果研究

为了研究配重位置对舵面颤振特性的影响,用有限元方法分析了舵面模态,用当地流活塞理论计算非定常气动力,应用Lagrange方程,建立基于模态坐标的颤振运动方程。研究表明:不同位置配重导致不同的颤振边界,放置于前缘与尖弦交点对提高临界动压效果最为明显;在工程设计中,不能简单的以质心前移或者增大扭转-弯曲频率比来指导全动舵面的颤振抑制设计,在前缘与根弦交点附近处加配重使得质心前移,甚至会使临界动压下降;配重通过削弱振型的耦合程度来抑制颤振,配重位置应尽量取在前缘与尖弦交点附近,使得弯、扭振型耦合程度削弱。     

考虑气核生长溃灭效应的螺旋桨梢涡空化初生数值模拟研究

梢涡空化是螺旋桨最早发生的空化类型,其一旦发生会显著增强舰船辐射噪声水平.因此,螺旋桨梢涡空化初生的预报是军舰临界航速确定的关键,长期以来受到船舶领域诸多专家学者的重点关注.微观气核受涡心低压作用而发生暴发式生长是梢涡空化初生的重要机制,而传统欧拉框架下的宏观空化模型用经验参数模化了微观气核的影响而无法对该过程准确模拟,影响对螺旋桨空化初生的准确预报.为了弥补传统模拟方法的不足,本研究发展并使用一种基于气泡动力学并考虑水相可压缩效应的欧拉-拉格朗日空化初生数值预报方法对螺旋桨梢涡空化初生进行了数值模拟研究.与实验结果对比表明,该模型能够准确地预报螺旋桨梢涡空化初生.此外,本研究不仅从微观气核角度探究不同来流气核尺寸对空化初生的影响,还进一步研究梢涡流动特性对气核演变的影响机制,初步探究初生空化在螺旋桨梢涡流场中的发声机理.在空化初生光学判断准则下尺寸越大的气核越容易被梢涡捕获而暴发式生长.气核在梢涡卷吸作用下逐渐靠近涡心低压区.在涡心低压区的持续作用下气核开始暴发式生长,并在半径达到最大后迅速收缩溃灭,产生强烈的正声压脉冲信号.     

基于涡旋识别方法的高速列车尾涡结构的讨论

利用改进型延迟分离涡模拟方法对缩尺比例1:30的高速列车简化模型的绕流流场进行数值计算,主要针对近尾流区的涡旋结构展开具体讨论. 通过不同的涡旋识别方法,发现在尾涡结构中,高涡量的强涡旋主要聚集于尾车附近,而涡量较低但处于相对稳定状态的涡旋分布在大部分尾流空间中. 对此,主要基于最新提出的涡旋定义及其物理意义认为,由于边界层在尾部发生的流动分离,剪切变形以及高涡量的扩散对强涡旋的形成发挥着重要的作用,而涡旋会被较强的剪切旋转拉伸,使得局部复杂的流动表现出突出的湍流特性;另一方面,尽管涡强度明显下降,但是在强剪切应变迅速衰减的情况下,流向涡核中的涡旋涡量是主要的,此时,在较接近地面的情况下,流体微团以涡核为中心的旋转运动使得涡旋与地面之间的相互作用成为主导的流动机制. 虽然涡强度会相对缓慢地衰减,但是从湍流能量产生的角度,该机制对涡旋的自维持发挥重要的作用,从而使尾涡结构能够相对稳定地存在于尾流流动中.      

基于结构化网格的导管螺旋桨敞水性能计算和艇桨干扰分析

本文采用结构化网格建模求解RANS方程,建立了导管桨和艇桨组合体的水动力性能数值计算方法.计算中以JD75简易导管与Ka4-70螺旋桨组合的导管螺旋桨及其与SUBOFF艇体模型的组合体为研究对象,利用RNG k-ε湍流模型封闭RANS方程得到控制方程.通过滑移网格方法计算了导管桨敞水性能,然后将该桨置于全附体SUBOFF潜艇模型后,计算螺旋桨与主艇体间的干扰特性,文中对流场等结果进行了分析比较.     

基于涡旋识别方法的高速列车尾涡结构的讨论

利用改进型延迟分离涡模拟方法对缩尺比例1:30的高速列车简化模型的绕流流场进行数值计算,主要针对近尾流区的涡旋结构展开具体讨论.通过不同的涡旋识别方法,发现在尾涡结构中,高涡量的强涡旋主要聚集于尾车附近,而涡量较低但处于相对稳定状态的涡旋分布在大部分尾流空间中.对此,主要基于最新提出的涡旋定义及其物理意义认为,由于边界层在尾部发生的流动分离,剪切变形以及高涡量的扩散对强涡旋的形成发挥着重要的作用,而涡旋会被较强的剪切旋转拉伸,使得局部复杂的流动表现出突出的湍流特性;另一方面,尽管涡强度明显下降,但是在强剪切应变迅速衰减的情况下,流向涡核中的涡旋涡量是主要的,此时,在较接近地面的情况下,流体微团以涡核为中心的旋转运动使得涡旋与地面之间的相互作用成为主导的流动机制.虽然涡强度会相对缓慢地衰减,但是从湍流能量产生的角度,该机制对涡旋的自维持发挥重要的作用,从而使尾涡结构能够相对稳定地存在于尾流流动中.     

全附体潜艇粘性流场的RANS模拟及场量和涡量的校验分析

采用相同拓扑结构和相近网格质量的4套网格和5种湍流模型,对全附体Suboff潜艇粘性流场进行RANS模拟,分析了网格密度、节点空间分布规律和湍流模型对计算精度的影响,详细校验了其力积分量、速度场量和涡量特征。结果表明:网格密度最大的G4网格(140万)计算精度最高,总阻力较实验值误差为0.723%,其采用SST湍流模型时最优。计算得到的压力系数和剪切应力系数分布均与实验值吻合很好;桨盘面速度等值线分布计算精度与文献相当,轴向相对速度0.9以上的计算半径稍大于实验值,其余半径与实验吻合较好;桨盘面上0.25倍半径处速度分量沿周向分布计算精度较文献高,轴向分量与实验值吻合较好,径向分量峰值稍小于实验值,但峰值所处周向位置与实验值一致。成功捕捉到了附体端面绕流诱导对旋涡、附体叶根截面下游处项链形涡对、尾翼端面尾缘上方附着涡蹄、附体马蹄涡系、尾翼截面通道流体挤压作用诱导涡以及桨盘面涡量汇集的潜艇涡量场特征,且围壳端面绕流诱导对旋涡沿流动方向持续稳定,不影响桨盘面涡量场,均与文献中由大涡模拟模拟得到的定性结论一致。研究表明,在网格密度较大、节点分布合理、网格质量较高、湍流模型选取适当和壁面函数使用有效的条件下,RANS模拟潜艇粘性流场的场量和涡量特征同样具有很高的计算精度,能够在工程应用中有力支撑新型艇型设计与性能分析。     

The wake flow downstream of a propeller-rudder system

We report wall-resolved, large-eddy simulations for the case of a propeller operating upstream of a hydrofoil, mimicking a rudder. Our primary objective is the identification of wake features that are unique to this coupled system, when compared to open-water cases, which are usually the focus of experiments and computations in the literature. We were able to achieve unprecedented levels of numerical resolution, which capture the dynamics of all energetic eddies in the flow by using a scalable, conservative, structured solver in cylindrical coordinates. The boundary conditions on the rotating propeller and hydrofoil were enforced via an immersed boundary formulation. The largest values of turbulent stresses in the wake of the hydrofoil are achieved outwards from the radial coordinate of the tip of the propeller blades. This is due to spanwise gradients across the hydrofoil (in the direction parallel to the span of the hydrofoil), producing a displacement of the pressure side legs of the tip vortices towards outer coordinates, where they experience shear with the wake of the hydrofoil. The evolution of turbulence is non-monotonic across the streamwise direction. This is a consequence of the growing shear resulting from the complex interactions involving the shear layers from the trailing edge, the tip vortices and the two branches of the hub vortex coming from the two sides of the hydrofoil. Such a shear is reinforced by the spanwise velocities developed by the two branches of the propeller wake across the hydrofoil. Compared to an isolated propeller, these phenomena enhance turbulence production. The present results highlight that a downstream hydrofoil, typical of surface ships, is able to significantly intensify the wake signature of a propeller.     

Coherent and turbulent process analysis of the effects of a longitudinal vortex on boundary layer detachment on a NACA0015 foil

In this paper, the influence of a single tip vortex on boundary layer detachment is studied. This study offers a preliminary approach in order to better understand the interaction between a propeller hub vortex and the rudder installed in its wake. This configuration belongs to the field of marine propulsion and encompasses such specific problem as cavitation inception, modification of propulsive performances and induced vibrations. To better understand the complex mechanisms due to propeller–rudder interactions it was decided to emphasize configurations where the hub vortex is generated by an elliptical 3-D foil and is located upstream of a 2-D NACA0015 foil at high incidences for a Reynolds number of 5×10⁵. The physical mechanisms were studied using Time Resolved Stereoscopic Particle Image Velocimetry (TR-SPIV) techniques. Particular attention was paid to the detachment at 25° incidence and a detailed cartography of the mean and turbulent properties of the wake is presented. Proper Orthogonal Decomposition (POD) analysis was applied in order to highlight the unsteady nature of the flow using phase averaging based on the first POD coefficients to characterize the turbulent and coherent process in the near wake of the rudder.     

Propeller tip and hub vortex dynamics in the interaction with a rudder

In the present paper, the interaction mechanisms of the vortices shed by a single-screw propeller with a rudder installed in its wake are addressed; in particular, following the works by Felli et al. (Exp Fluids 6(1):1–11, 2006a, Exp Fluids 46(1):147–1641, 2009a, Proceedings of the 8th international symposium on particle image velocimetry: Piv09, Melbourne, 2009b), the attention is focused on the analysis of the evolution, instability, breakdown and recovering mechanisms of the propeller tip and hub vortices during the interaction with the rudder. To investigate these mechanisms in detail, a wide experimental activity consisting in time-resolved visualizations, velocity measurements by particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) along horizontal chordwise, vertical chordwise and transversal sections of the wake have been performed in the Cavitation Tunnel of the Italian Navy. Collected data allows to investigate the major flow features that distinguish the flow field around a rudder operating in the wake of a propeller, as, for example, the spiral breakdown of the vortex filaments, the rejoining mechanism of the tip vortices behind the rudder and the mechanisms governing the different spanwise misalignment of the vortex filaments in the pressure and suction sides of the appendage.     

PIV analysis of flow around a container ship model with a rotating propeller

The flow characteristics of the propeller wake behind a container ship model with a rotating propeller were investigated using a two-frame PIV (Particle Image Velocimetry) technique. Ensemble-averaged mean velocity fields were measured at four different blade phases and ensemble-averaged to investigate the flow structure in the near-wake region. The mean velocity fields in longitudinal planes show that a velocity deficit is formed in the regions near the blade tips and hub. As the flow develops in the downstream direction, the trailing vortices formed behind the propeller hub move upward slightly due to the presence of the hull wake and free surface. Interaction between the bilge vortices and the incoming flow around the hull causes the flow structure to be asymmetric. Contour plots of the vorticity give information on the radial distribution of the loading on the blades. The radial velocity profiles fluctuate to a greater extent under the heavy (J=0.59) and light loading (J=0.88) conditions than under the design loading condition (J=0.72). The turbulence intensity has large values around the tip and trailing vortices. As the wake develops in the downstream direction, the strength of the vorticity diminishes and the turbulence intensity increases due to turbulent diffusion and active mixing between the tip vortices and the adjacent wake flow.     

单一水平轴风电机组尾迹的模拟方法与流动机理研究综述

为实现碳达峰、碳中和“3060”目标, 风能将在我国能源体系发挥重要作用. 风力机尾迹是影响风电性能和度电成本的关键因素, 需在风力机布置和控制设计中充分考虑. 本文首先介绍风力机尾迹的数值模拟方法, 包括解析模型、低阶模型、大涡模拟和来流湍流生成方法. 解析模型和低阶模型可快速计算风力机尾迹, 但依赖于模型参数, 且不能或不能准确预测尾迹湍流特性. 结合风力机参数化模型的大涡模拟可准确预测尾迹蜿蜒等湍流特征, 是流动机理研究的有力工具, 可为发展快速预测模型提供数据和理论支撑. 接着, 本文介绍了叶尖涡、中心涡和尾迹蜿蜒并讨论其产生机理. 对于湍流来流, 叶尖涡主要存在于近尾迹. 蜿蜒是远尾迹的主要特征, 影响下游风力机的来流特征. 尾迹蜿蜒的产生有两种机制: 来流大尺度涡和剪切层失稳. 数值和观测结果显示两种机制共同存在. 机舱和中心涡对尾迹蜿蜒有重要影响. 采用叶片和机舱的致动面模型可准确预测尾迹蜿蜒. 研究显示不同风力机尾迹间的湍流特征存在相似性, 为发展尾迹湍流的快速预测模型提供了理论依据. 当前研究多关注平坦地形上的风力机尾迹, 复杂地形和海洋环境下的大气湍流和风力机尾迹的机理复杂, 现有工程模型无法准确预测, 有待深入研究.      

Near-wake flow structure downwind of a wind turbine in a turbulent boundary layer

Wind turbines operate in the surface layer of the atmospheric boundary layer, where they are subjected to strong wind shear and relatively high turbulence levels. These incoming boundary layer flow characteristics are expected to affect the structure of wind turbine wakes. The near-wake region is characterized by a complex coupled vortex system (including helicoidal tip vortices), unsteadiness and strong turbulence heterogeneity. Limited information about the spatial distribution of turbulence in the near wake, the vortex behavior and their influence on the downwind development of the far wake hinders our capability to predict wind turbine power production and fatigue loads in wind farms. This calls for a better understanding of the spatial distribution of the 3D flow and coherent turbulence structures in the near wake. Systematic wind-tunnel experiments were designed and carried out to characterize the structure of the near-wake flow downwind of a model wind turbine placed in a neutral boundary layer flow. A horizontal-axis, three-blade wind turbine model, with a rotor diameter of 13 cm and the hub height at 10.5 cm, occupied the lowest one-third of the boundary layer. High-resolution particle image velocimetry (PIV) was used to measure velocities in multiple vertical stream-wise planes (x–z) and vertical span-wise planes (y–z). In particular, we identified localized regions of strong vorticity and swirling strength, which are the signature of helicoidal tip vortices. These vortices are most pronounced at the top-tip level and persist up to a distance of two to three rotor diameters downwind. The measurements also reveal strong flow rotation and a highly non-axisymmetric distribution of the mean flow and turbulence structure in the near wake. The results provide new insight into the physical mechanisms that govern the development of the near wake of a wind turbine immersed in a neutral boundary layer. They also serve as important data for the development and validation of numerical models.     

Three-component velocity field measurements of propeller wake using a stereoscopic PIV technique

A stereoscopic PIV (Particle Image Velocimetry) technique was used to measure the three-dimensional flow structure of the turbulent wake behind a marine propeller with five blades. The out-of-plane velocity component was determined using two CCD cameras with an angular displacement configuration. Four hundred instantaneous velocity fields were measured for each of four different blade phases, and ensemble averaged in order to find the spatial evolution of the propeller wake in the region from the trailing edge up to one propeller diameter (D) downstream. The influence of propeller loading conditions on the wake structure was also investigated by measuring the velocity fields at three advance ratios (J=0.59, 0.72 and 0.88). The phase-averaged velocity fields revealed that a viscous wake formed by the boundary layers developed along the blade surfaces. Tip vortices were generated periodically and the slipstream contracted in the near-wake region. The out-of-plane velocity component and strain rate had large values at the locations of the tip and trailing vortices. As the flow moved downstream, the turbulence intensity, the strength of the tip vortices, and the magnitude of the out-of-plane velocity component at trailing vortices all decreased due to effects such as viscous dissipation, turbulence diffusion, and blade-to-blade interaction.     

Spatial perturbation of a wing-tip vortex using pulsed span-wise jets

The separation distance required between transport aircraft to avoid wake vortices remains a limiting factor on airport capacity. The dissipation of the wake can be accelerated by perturbing co-operative instabilities between multiple pairs of vortices. This paper presents the results of a preliminary experimental investigation into the use of pulsed span-wise air jets in the wing tip to perturb a single tip vortex in the very near field. Velocity measurements were made using PIV and hot-wire anemometry. The results demonstrate that the vortex position can be modulated at frequencies up to 50 Hz and, as such, the method shows promise for forcing instability in multiple vortex wakes.     

Experimental analysis of the flow field around a propeller–rudder configuration

The problem of an isolated free-running propeller–rudder combination is tackled in the present paper. The activity concerns phase-averaged velocity measurements by LDV along two transversal planes of the wake, just in the front and behind the rudder. In addition, visualizations of the chordwise interaction between the tip vortex filaments and the rudder, performed using a time resolved CMOS camera, are presented. The major phenomena that affect the performance of a rudder in the race of a propeller, with special emphasis on unsteady-flow aspects, are highlighted in this paper.