艇尾实尺桨空化初始航速和高频噪声谱的工程预报

为了实现艇尾实尺桨空化初始航速和高频噪声谱的工程预报,采用模型桨空化多相流模拟和实桨高频噪声谱半经验公式预报相结合的方法,预报了SUBOFF潜艇标称伴流下的实尺度7叶大侧斜桨的空化初始航速和高频噪声谱曲线以及特定频率1kHz处的谱源级。空化模拟和空化初生的较高预报精度由E779A桨的空化形态、空化面积和初生空化数的预报给予了校验。半经验公式的适用性由USS212型潜艇和Agosta-80潜艇的螺旋桨噪声预报给予了校验,精度适中。计算结果表明:7叶桨在水深16.8 m时空化初始航速为12.8 kn,6 kn航速下1 kHz处谱级为101.7 dB,较相同水深下Agosta-80潜艇临界航速高2.6 kn、谱级低0.3 dB,表明噪声性能更优。较好地建立了艇尾实尺桨空化初始航速和高频噪声谱预报的工程应用方法。     

A BEM for the modeling of unsteady propeller sheet cavitation inside of a cavitation tunnel

A boundary element method is applied to predict the unsteady cavitating performance of marine propellers subject to a non-axisymmetric inflow with the complete tunnel wall effect. The tunnel and propeller problem is solved directly to predict the fully unsteady performance of the cavitating propeller. The cavitation on blade and wake surface is determined by applying the dynamic and the kinematic boundary conditions on the cavity surface. The potential on the cavity surface is known from the dynamic boundary condition and the relation between cavitation number and cavity velocity. Once the boundary value problem is solved for the unknowns- the potentials on the wetted blade surface and the normal derivative of potentials on the cavity surface – the new cavity shape is adjusted by using the normal derivative of the potential. The potential on the new cavity surface is determined by using the kinematic boundary condition on the cavity. The procedure is repeated until the cavity shape converges and the pressure on the cavity becomes constant. To validate the present method, the effects of the number of blade panels and the dimensions of the tunnel walls on blade forces are presented. The predicted cavity patterns are compared with those observed from experiment.     

Numerical simulation of cryogenic cavitating flow by an extended transport-based cavitation model with thermal effects

Thermodynamic effects on cryogenic cavitating flow is important to the accuracy of numerical simulations mainly because cryogenic fluids are thermo-sensitive, and the vapour saturation pressure is strongly dependent on the local temperature. The present study analyses the thermal cavitating flows in liquid nitrogen around a 2D hydrofoil. Thermal effects were considered using the RNG k-ε turbulence model with a modified turbulent eddy viscosity and the mass transfer homogenous cavitation model coupled with energy equation. In the cavitation model process, the saturated vapour pressure is modified based on the Clausius-Clapron equation. The convection heat transfer approach is also considered to extend the Zwart-Gerber-Belamri model. The predicted pressure and temperature inside the cavity under cryogenic conditions show that the modified Zwart-Gerber-Belamri model is in agreement with the experimental data of Hord et al. in NASA, especially in the thermal field. The thermal effect significantly affects the cavitation dynamics during phase-change process, which could delay or suppress the occurrence and development of cavitation behaviour. Based on the modified Zwart-Gerber-Belamri model proposed in this paper, better prediction of the cryogenic cavitation is attainable.     

船舶螺旋桨叶片与艉部湍流场互作用噪声的预报研究

低噪声特性是螺旋桨设计者所追求的目标之一。当船尾的螺旋桨周期性旋转在空间和瞬时随机的非均匀流场中时,在螺旋桨叶片上就会产生升力脉动,从而辐射出离散谱噪声和低频宽带噪声。利用湍流谱和FfowcsWilliams-Hawkings方程可以获得低频宽带噪声级。这种方法可用于实船螺旋桨噪声预报和低噪声设计,这对提高舰船安静化程度有重要的现实意义。     

锯齿形叶梢螺旋桨高负荷水动力和减振降噪特性试验研究

本文用涡动力学理论分析了锯齿形叶梢对螺旋浆的梢涡的影响，在拖曳水池中分别对常规、后倾且倾斜和后缘锯齿形叶梢的螺旋浆模型进行了水动力特征试验。在大型空泡水洞中的模拟伴流场中分别对这三种形状叶梢的螺旋浆模型进行了高负荷水动力时的脉动压力和噪声测试，试验结果表明，用锯齿形叶梢螺旋浆在高负荷时效率可提高2．5％，激振力降低44．2％，噪声下降3－5dB。而这一切是在用后倾侧斜叶梢螺旋浆已经取得了明显增效和减振降噪效果的基础上又增加的效果，试验验证了用涡量汇的理论分割浆叶梢涡的设计思想是正确的和可行的。     

Particle swarm optimization: an alternative in marine propeller optimization?

This article deals with improving and evaluating the performance of two evolutionary algorithm approaches for automated engineering design optimization. Here a marine propeller design with constraints on cavitation nuisance is the intended application. For this purpose, the particle swarm optimization (PSO) algorithm is adapted for multi-objective optimization and constraint handling for use in propeller design. Three PSO algorithms are developed and tested for the optimization of four commercial propeller designs for different ship types. The results are evaluated by interrogating the generation medians and the Pareto front development. The same propellers are also optimized utilizing the well established NSGA-II genetic algorithm to provide benchmark results. The authors' PSO algorithms deliver comparable results to NSGA-II, but converge earlier and enhance the solution in terms of constraints violation.     

基于拉格朗日方法的非定常空化流动研究

采用基于拉格朗日体系的有限时间李雅普诺夫指数、拉格朗日拟序结构和粒子追踪方法对绕水翼典型非定常云状空化流场进行研究。采用计算流体动力学方法获得空化流场数据数值,湍流模型采用经典大涡模拟方法,空化相变过程采用基于相间质量传输的Zwart模型进行处理。根据有限时间李雅普诺夫指数分布在空化核心区域定义了前缘拟序结构和尾缘拟序结构。在不同的空化发展阶段,两种拟序结构相互作用并呈现不同的分布规律,揭示不同空化发展阶段的典型流场结构。     

A Marine Propeller Aerodynamic Test Facility

Abstract:  Conventional propeller test facilities such as tow tanks, cavitation tunnels and the open sea have various limitations such as cost, accessibility, size and accuracy. An aerodynamic marine propeller test facility has been developed at the University of British Columbia to allow for performance evaluations of full-size marine propellers in the highly controlled environment of a wind tunnel. Thorough static and dynamic calibrations of the test rig confirmed that the sensors have a highly linear response with essentially zero crosstalk between the thrust and torque signals. Performance curves acquired from a commercial 24 × 24 propeller show that the repeatability error of the torque and thrust measurements is <1%. The uncertainties of the advance ratio, torque coefficient, thrust coefficient, and efficiency are 0.2%, 0.5%, 0.1%, and 1%, respectively. Performance curves measured over a range of the Reynolds numbers show that Reynolds number independence is achieved for Reynolds numbers above approximately 5 × 10⁵.     

大涡模拟预报螺旋桨辐射噪声的三种声学方法

螺旋桨噪声是船舶的三大噪声源之一,研究螺旋桨的噪声现象具有很大的现实意义。首先划分了螺旋桨的结构化网格,进行了网格收敛性分析,然后采用大涡模拟方法计算螺旋桨水动力。在噪声计算中采用了FW-H方程、结合Virtual lab的旋转偶极子辐射、涡声方程三种方法进行预报,并与换算到自由场的试验结果进行对比分析。结果表明,采用大涡模拟可以预报螺旋桨的辐射噪声,三种方法均满足工程应用需求。     

空调室内机贯流风扇流动噪音的仿真研究

空调室内机空气流动噪音是影响室内舒适性的重要因素,为此对室内机贯流风扇的非定常流场及噪音特性进行了数值分析。采用非均匀滑移网格和RNG k-ε湍流模型对不可压缩流体非定常流动的Navier-Stokes方程进行求解,并采用Ffowcs-Williams and Hawkings模型对空气流场和噪音进行关联,对空调室内机内空气非定常流场及流动噪音进行数值分析,并与实验结果进行比较。结果表明,采用此方法对计算的流动噪音的声音品质和声谱特性都与测量结果有较好的吻合,为空调器空气流场的优化设计和降低空调器风扇及空气流动噪音的研究提供了有效工具。     

Analysis of supercavitating and surface-piercing propeller flows via BEM

A low-order potential based 3-D boundary element method (BEM) is presented for the analysis of unsteady sheet cavitation on supercavitating and surface-piercing propellers. The method has been developed in the past for the prediction of unsteady sheet cavitation for conventional propellers. To allow for the treatment of supercavitating propellers, the method is extended to model the separated flow behind trailing edge with non-zero thickness. For surface-piercing propellers, the negative image method is used, which applies the linearized free surface boundary condition with the infinite Froude number assumption. The method is shown to converge quickly with grid size and time step size. The predicted cavity planforms and propeller loadings also compare well with experimental observations and measurements. This work was completed while as a doctoral student at The University of Texas at AustinSupport for this research was provided by Phase III of the Consortium on Cavitation Performance of High Speed Propulsors with the following members: AB Volvo Penta, American Bureau of Shipping, El Pardo Model Basin, Hyundai Maritime Research Institute, Kamewa AB, Michigan Wheel Corporation, Naval Surface Warfare Center Carderock Division, Office of Naval Research (Contract N000140110225), Ulstein Propeller AS, VA Tech Escher Wyss GMBH, and Wärtsilä Propulsion.     

船舶螺旋桨辐射噪声与尾流场的相关性及特征分析方法

研究螺旋桨几何特征和工况特征变化对螺旋桨尾流场和噪声特征的影响。采用黏性多相流理论对螺旋桨尾流场特征进行数值预报。利用N-S方程、混合多相流模型、湍流模型和空化模型数值求解尾流场压力脉动等物理量。将压力脉动数值解和测量噪声声压信号的功率谱低频线谱特征进行分析,表明两者特征具有一定的相关性。最后分析侧斜角和进速系数对压力信号频谱特征的影响,获得了低频线谱幅值分布特征与螺旋桨侧斜角、进速系数等参数的初步关系。     

轴对称体空化水动力脉动特性的实验研究

为了研究轴对称体非定常空化的脉动特性,采用高速全流场显示技术和动态测力系统实验研究了绕半球型和平头轴对称体的非定常空化流场及其动力特性。实验在闭式水洞中进行,采用高速摄影的方法观察了在不同空化数下绕半球型和平头轴对称体的空穴形态,总结了在不同空化数下空泡形态的脉动特性;测量了轴对称体受到的阻力,并对阻力信号进行了时频分析,得到了轴对称体阻力在非定常空化阶段的时频特征。结果表明:空泡形态及其对应的动力特征随着空化数的变化存在明显的非定常特性,空化流场形态与动力特征频率存在高度的相关性。并且不同头型轴对称体的脉动特性存在明显的差异,半球型轴对称体空泡流动的脉动主要是空泡尾部的高频小脱落引起的,而平头轴对称体的空泡流脉动成分主要是大尺度的漩涡空泡团的周期性脱落,空化流场的低频特征频率与空泡的大断裂相对应。     

绕三维水翼非定常空化流动结构的数值与实验研究

为了说明非定常空化的流动机理,该文采用数值与实验相结合的方法对绕三维水翼片状和云状空化流动结构进行了研究.实验在高速水洞中进行,采用高速录像技术观测了片状和云状空化阶段的空穴形态.数值计算基于均相流模型,汽液混合区域密度由质量传输方程调节.利用商业软件二次开发技术引入准确描述空化流场非定常特性的FBM 湍流模型,进行绕三维水翼的数值模拟,获得了随时间变化的空穴形态、压力和速度分布等流场结构.与实验结果对比发现,数值计算结果与实验基本一致.在片状空化阶段,空穴稳定地附着在水翼表面,只有空穴尾部不断的有小空泡团沿着翼弦方向脱落.在云状空化阶段,清楚得描述了空穴的产生-发展-脱落-溃灭的准周期性变化,并准确地捕捉到空泡脱落时,附着在翼型前端的U 型空穴和翼展方向不同强度的反向射流,脱落的空泡由翼型中前部旋涡状脱落.     

浸没排气过程声信号与流场振荡规律研究

采用流体体积(Volume of Fluid,VOF)模型和威廉姆斯-霍金斯(Ffowcs Williams and Hawkings,FW-H)模型对浸没排气过程声信号进行数值模拟,研究竖直向下浸没排气过程声信号产生机制及理论依据。将模拟结果与实验结果进行对比,验证模型的适用性和准确性。研究结果表明,声信号与流场流动状态相关,气泡间分离和气体再注入过程引起的气泡体积剧烈振动是影响气泡流声信号产生的关键因素。在同一深度处,在径向上声压随位置的变化服从指数衰减,在周向上声信号呈现球源信号传播特点。     

叶轮隔舌间隙对离心泵性能和流动噪声影响的试验研究

搭建了离心泵流动诱导噪声测试台,采用四端网络法声学测试模型,试验研究了离心泵性能和流动噪声随流量的变化规律,分析了空化发生时的流动噪声特性。通过研究不同叶轮切割量对模型泵外特性、流动噪声声压级和空化性能的影响,提出叶轮和隔舌之间的最佳间隙值。研究结果表明：在高效区运行时,模型泵进出口流动诱导噪声均随流量先减小,至效率最高工况点达到最小,然后上升;各流量下,随着空化余量的减小,模型泵进口噪声总声压级先缓慢增加,再迅速上升,达到极值后缓慢下降;随着叶轮切割量的增加,模型泵扬程跟叶轮直径的平方成正比,最高效率点向小流量工况偏移,临界空化余量变小;综和性能和流动噪声考虑,模型泵叶轮和隔舌的最佳间隙率为15%;在间隙值小于最佳值时,切割叶轮能显著降低噪声并提高模型泵的临界空化余量,并且对模型泵出口流动噪声的影响比进口明显。     

Semianalytical solution of unsteady quasi-one-dimensional cavitating nozzle flows

Unsteady quasi-one-dimensional bubbly cavitating nozzle flows are considered by employing a homogeneous bubbly liquid flow model, where the nonlinear dynamics of cavitating bubbles is described by a modified Rayleigh–Plesset equation. The model equations are uncoupled by scale separation leading to two evolution equations, one for the flow speed and the other for the bubble radius. The initial-boundary value problem of the evolution equations is then formulated and a semianalytical solution is constructed. The solution for the mixture pressure, the mixture density, and the void fraction are then explicitly related to the solution of the evolution equations. In particular, a relation independent of flow dimensionality is established between the mixture pressure, the void fraction, and the flow dilation for unsteady bubbly cavitating flows in the model considered. The steady-state compressible and incompressible limits of the solution are also discussed. The solution algorithm is first validated against the numerical solution of Preston et al. [Phys Fluids 14:300–311, 2002] for an essentially quasi-one-dimensional nozzle. Results obtained for a two-dimensional nozzle seem to be in good agreement with the mean pressure measurements at the nozzle wall for attached cavitation sheets despite the observed two-dimensional cavitation structures.     

Effects of Bend–Twist Coupling on Composite Propeller Performance

An investigation of a conventional propeller, made from composite materials, was conducted in which propeller characteristics were studied under quasi-static aerodynamic loading. Emphasis was placed on understanding the effects of bend-twist coupling of composite laminates on propeller performance. The classical blade element theory of propellers was used to calculate propeller characteristics and the aerodynamic force distribution acting on the propeller. The finite-element method was used to calculate the resulting deformation of the propeller blades. A simple algorithm was used in which propeller blade deformation and resulting changes in loading conditions were calculated repeatedly until equilibrium between deformation and loading was achieved. Results show that improvements in propeller performance are possible using the bend-twist coupling of composite laminates. Additionally, this study shows that the numerical approach developed by the authors is well suited for analyzing the performance characteristics of composite propellers.     

Interference-free tool path generation in five-axis machining of a marine propeller

The manufacture of a marine propeller typically requires long lead-time to generate five-axis tool paths. It usually takes several days to generate satisfactory tool paths with a general purpose CAD/CAM system. This paper proposes a novel methodology that generates effective five-axis tool paths for marine propellers. The machining of a propeller is accomplished in three steps: rough cut, semi-finish cut, and finish cut. For generating accurate finish cut tool paths, the proposed system computes check vectors that determine a maximum range of valid tool motion based upon tool size and passage width for each CL (Cutter Location) point along the tool path. Interference-free tool paths can be acquired by positioning the tool inside the two check vectors. The modelling capability for propellers is also of importance because it determines the eventual success or failure of the whole process. An iterative B-spline surface modelling technique is employed to improve the accuracy of the models and to increase the productivity. The proposed system generates interference-free tool paths with superior surface finish and reduces lead-time to manufacture a propeller. The system validation and sample results are given and discussed.     

螺旋桨模型喷气降噪试验与实船效果预报研究

螺旋桨若发生空化,空化就是全船最主要的辐射噪声源。采用喷气降噪技术可以降低螺旋桨的空化噪声。试验证实,在螺旋桨推力损失不大时,采用导边喷气、喷气环喷气、组合喷气三种方式都可以使噪声谱级大幅下降。根据喷气孔出口速度的无量纲值相等可以换算出实船喷气量。实船预报表明,采用喷气后总声级降低5 d B以上。