用多重网格法数值预测高速离心叶轮三维流场

研究离心叶轮压气机性能优化问题,针对发展迅速、准确预测复杂流动离心压气机的性能设计是非常必要的.传统方法用显式时间推进法效率低、收敛速度慢等缺点,采用隐式残差光顺以及基于变分原理的多重网格方法,具有计算效率高、收敛速度快等特点的数值仿真,采用改进的数值算法对内部三维粘性流场进行了数值仿真,给出了多重网格重数对收敛速度的影响,数值预测了不同流量下的流场流动情况,并与实验结果进行了比较.研究结果表明,多重网格可以有效地加速收敛,数值结果与试验结果吻合较好,改进的数值方法可以较好的预测离心叶轮的性能.     

Helmholtz共振腔气动噪声数值仿真

为探究出一套完整、准确的气动噪声仿真方法,用FLUENT和Actran仿真Helmholtz共振腔旁接管道系统模型.针对流场仿真,采用六面体网格建模,分析选择合适的网格密度,明确网格及边界条件的影响,以获得准确的声源信息;运用Lighthill声类比方法对声场进行仿真,采用数值计算、传声损失仿真和气动噪声仿真计算等3种方法提取管道内部场点声压级频谱曲线,分析曲线峰值频率特征,包括共振频率分析和声模态分析等.采用CFD软件与声学仿真软件相结合的方法,可以有效进行流场和声场的仿真.     

基于动网格的水疗按摩喷嘴转动模拟

为克服靠经验设计水疗（SPA）按摩喷嘴成本高、周期长的缺点,利用计算流体力学（Computational Fluid Dynamics,CFD）技术对某水疗按摩喷嘴进行数值建模、仿真和计算,以优化喷嘴结构．首先求出动网格守恒方程,然后利用FLUENT的动网格模型和自定义的喷嘴转动UDF,对喷嘴的转子进行三维数值分析,实现转子的网格转动,并求出转动速度．实验和仿真结果对比表明所采用的方法是合适的．     

基于DLM法与CFD法的飞机平尾气动力计算比较

为提高飞机平尾的结构计算精度,利用HyperMesh同时建立结构网格与流场网格,在翼面结构与流场中物面节点坐标位置完全相同的情况下,分别采用偶极子格网法(Double-Lattice Method,DLM)与计算流体力学(Computational Fluid Dynamics,CFD)法计算飞机平尾负攻角变化时的升力变化情况.在HyperMesh中建立平尾有限元模型和流体模型,用FLUENT计算气动升力,用MSC Nastran进行静力分析.计算结果与实验结果的对比表明DLM更快,CFD法更精确,所以可以在翼面设计初期用DLM计算翼面载荷,在翼面设计后期用CFD法计算翼面载荷.     

结构化多重网格粘性流场数值模拟

流体力学控制方程的数值求解过程中,当网格加密或者粘性效应强的时候,流场收敛非常缓慢.为了解决计算的效率问题,在结构网格的基础上采用多重网格技术,模拟了二维RAE2822超临界翼型的亚音速绕流及三维M6机翼跨音速流场,仿真结果表明,采用多重网格方法在二维,三维粘性流场的计算结果都与实验结果吻合良好,与不采用多重网格方法比较,在求解中获得了相当满意的加速收敛效果.还比较了两种不同循环方式:V循环,W循环的加速效率,为多重网格的工程应用奠下基础.     

旋风分离器减阻杆减阻的数值研究

文中首次利用数值方法对旋风分离器进行了减阻杆减阻的研究。应用CFD计算流体力学软件FLUENT，对某种型号的Stairmand高效型旋风分离器的三维有旋流场速度和压力进行了数值模拟，计算了减阻杆的减阻效率。流场和减阻效率的数值结果与实验数据吻合较好，证明对旋风分离器减阻杆减阻研究时所采用的网格划分方法、RSM湍流模型和边界条件是可靠的，为数字设计高效率的减阻杆提供了简便可靠的办法。     

基于FLUENT的气液分离器内流场仿真研究

基于计算流体动力学(CFD)方法,应用流体仿真软件FLUENT对两种气液分离装置内部流场进行仿真研究,得到分离器内部流场速度分布规律和相分布规律,发现合理改变排气通道的直径,可以提高分离效率。同时分析比较了流场模拟结果,发现排气通道直径改变处存在涡流。     

气液两相圆锥绕流的数值仿真

研究锥形物体在气液两相流场中动特性问题,对流场特性的影响和锥形物体自身的承载受力情况;采用CFD流体仿真软件FLUENT,用欧拉双流体模型结合Realizablek-ε湍流模型,对锥体在气液两相流场中的运动进行数值仿真.结果显示,在锥体尾部形成一组对称的回流涡,随着流体含液率的增加,主相空气相在中心轴线上的流向速度明显受到影响,尾涡变短,恢复速度变快;在绕流体的壁面上的流场的速度梯度会增大;同时绕流体周围的流场的压力梯度也会增大,湍动能和湍动能增量都会增大,与实验的结果基本吻合,验证了运用数值仿真的方法来研究气液两相锥体绕流问题是正确可行的.     

基于ANSYS/LS-DYNA的返回舱海面撞水动力研究

在理论分析刚形体垂直撞水动力特性的基础上,分别推导出基于von Karman理论和通用Wagner理论的圆球底返回舱撞水冲击过载公式.然后借助ANSYS/LS-DYNA动力显式程序中ALE算法的优势,进行返回舱海向垂直撞水动力数值仿真;针对数值仿真结果和理论分析预报结果的比较分析来验证数值仿真的可行性,同时给出数值计算弹性体模型垂直撞水的撞水冲击过载;结果表明:采用ANSYS/LS-DYNA的ALE算法可以有效地数值模拟返回舱撞水动力特性,为进一步控制返回舱海面回收以及数值分析撞水动力特性提供有力的技术支持,且大大节约了试验经费.     

闸阀扰流对外夹式超声流量计测量精度影响研究

受管路内不稳定流场的影响,外夹式超声流量计超声波传播声道上的流量计算模型改变,进而产生测量误差。采用计算流体动力学（CFD）仿真计算方法对50%闸阀开度时的管路流场进行了仿真分析,研究了闸阀前后不同位置处流场变化引起的流速变化情况,并在不同位置处提取多个声道的线平均速度进行比较,分析了选取不同声道时超声流量计的测量误差。最后,通过开展多声道超声流量计实测实验对CFD仿真计算结果进行了验证。     

Performance analysis of a wave energy converter using numerical simulation technique

A general purpose viscous flow solver Ansys CFX was used to study a Savonius type wave energy converter in a 3D numerical viscous wave tank.This paper presents the results of a computational fluid dynamics(CFD) analysis of the effect of blade configuration on the performance of two Savonius rotors for wave energy extraction.A piston-type wave generator was incorporated in the computational domain to generate the desired incident waves.A complete OWC system with a 3-bladed Savonius rotor was modeled in a thr...     

汽轮机转子碰摩热弯曲动力特性研究

本文简化了汽轮机转子模型,并根据转子碰摩理论建立了一种简单的求解碰摩截面热分布的计算模型,使得碰摩截面热分布的计算大大简化.依据转子动力学理论推导了本模型的运动方程,并作无量纲化以便于MATLAB数值求解收敛,最终建立了转子系统由摩擦引起的弹性热弯曲——碰摩耦合故障动力模型.利用四阶Runge-Kutta方法求解微分方程组得到了在不平衡力、碰摩力和碰摩热弯矩耦合作用下转子系统的响应,并对低于、接近和高于临界转速下碰摩热弯曲转子的动力学特性进行了数值仿真研究,包括时域、频谱、轴心轨迹以及碰摩力的变化.结果表明,转子在低于和接近临界转速运行发生碰摩,转子的振动由平稳状态逐渐发散,而在高于临界转速发生碰摩时转子的振动会逐渐减小.     

Design, modeling and first experimentation of a two-degree-of-freedom spherical actuator

This paper deals with the design of a two-actuated-degree-of-freedom (DOF) spherical electrical actuator for mobile robotic applications. It presents the different steps involved in this design, namely the choice of the actuation principle (induction), its application to the case of a spherical geometry and two DOFs, the analytical and numerical modeling of the motor, and the sizing and the manufacture of a first one-actuated-DOF spherical prototype. The first experimental results, obtained thanks to our test bench and presenting the torque vs rotor angular speed characteristic of the actuator, are likewise compared with the model predictions.     

Augmenting simulations of airflow around buildings using field measurements

Computational fluid-dynamics (CFD) simulations have become an important tool for the assessment of airflow in urban areas. However, large discrepancies may appear when simulated predictions are compared with field measurements because of the complexity of airflow behaviour around buildings and difficulties in defining correct sets of parameter values, including those for inlet conditions. Inlet conditions of the CFD model are difficult to estimate and often the values employed do not represent real conditions. In this paper, a model-based data-interpretation framework is proposed in order to integrate knowledge obtained through CFD simulations with those obtained from field measurements carried out in the urban canopy layer (UCL). In this framework, probability-based inlet conditions of the CFD simulation are identified with measurements taken in the UCL. The framework is built on the error-domain model falsification approach that has been developed for the identification of other complex systems. System identification of physics-based models is a challenging task because of the presence of errors in models as well as measurements. This paper presents a methodology to estimate modelling errors. Furthermore, error-domain model falsification has been adapted for the application of airflow modelling around buildings in order to accommodate the time variability of atmospheric conditions. As a case study, the framework is tested and validated for the predictions of airflow around an experimental facility of the Future Cities Laboratory, called “BubbleZERO”. Results show that the framework is capable of narrowing down parameter-value sets from over five hundred to a few having possible inlet conditions for the selected case-study. Thus the case-study illustrates an approach to identifying time-varying inlet conditions and predicting wind characteristics at locations where there are no sensors.     

Airflow in a slot-ventilated enclosure partially filled with porous boxes: Part I - Measurements and simulations in the clear region

A reduced-scale model and CFD predictions were used to investigate experimentally and numerically the airflow patterns within a ceiling slot-ventilated enclosure partially loaded with vented boxes filled by spherical objects. The experiments were carried out using laser Doppler velocimetry. Airflows around and inside porous boxes were predicted taking into account their aerodynamic interactions. This work is divided into two parts. This paper presents part I and concerns the air velocity characteristics within the jet above the boxes, while Part II deals with the air velocity characteristics inside the boxes. The results highlight the confinement effect due to the enclosure and the influence of load porosity on jet penetration, its development and hence the heterogeneity of ventilation within the enclosure. The numerical predictions obtained with the computational fluid dynamics Fluent package using the RSM turbulence model show reasonable agreement with experimental data. Predicted velocity profiles were generally within an error of 3-30% of the measured velocities.     

滚动转子压缩机转子组合结构振动特性分析与测试

为了避免压缩机转子系统在工作过程中的振动超标,需要对其开展系统化的动态优化设计,包括压缩机转子乃至整机的振动特性测试以及利用转子动力学对其建模与分析.本文以转子系统组合件(泵组件+外壳组件)为研究对象,首先创建了压缩机转子系统三维实体有限元分析模型.进一步,对转子系统的固有特性进行了分析,获得了前5阶固有频率与模态振型.最后,对该滚动转子压缩机进行了动力学实验,校验了上述分析模型的合理性.本文的研究可为压缩机系统的减振与降噪提供技术参考.     

CFD modeling of scale effects on turbulence flow and scour around bridge piers

Sediment scour near bridge piers is a problem of nationwide concern because it has resulted in more bridge failures than all other causes in recent years. The existing bridge scour equation from HEC-18 was developed from laboratory experiments in relatively small scale. Field studies by Mueller [Mueller D, Wagner Chad R. Analysis of pier scour predictions and real-time field measurements. In: Proceedings of ICSF-1 first international conference on scour of foundations, Texas A&M University, College Station, Texas, USA; 2002] indicate that it is difficult to verify the scour equation with field data obtained from large bridge piers. In this study, computational model simulations using a 3D CFD model were conducted to examine scale effects on turbulent flow and sediment scour. For the large-scale model, the physical scale and boundary velocity were set up from the small scale model based on the Froude similarity law. Results of flow and sediment scour were obtained from two different approaches: (a) Froude similarity which is commonly used in physical modeling and (b) full scale 3D CFD modeling. Unlike physical modeling in which the effect of turbulent Reynolds number is ignored, the CFD model employs a 2nd order turbulent model to calculate turbulent velocity and sediment scour. Effects of scale on turbulence flow and sediment scour were investigated by comparing different results obtained from a full scale numerical model to those derived from the Froude similarity method.     

Theoretical vibration analysis of soft mounted electrical machines regarding rotor eccentricity based on a multibody model

The paper presents a simplified multibody model of a soft mounted electrical machine for theoretical vibration analysis, considering different kinds of rotor eccentricity. The most important dynamic eccentricities in electrical machines—eccentricity of rotor mass, magnetic eccentricity, and bent rotor deflection—are analyzed. The aim of the paper is not to replace a detailed three-dimensional finite-element calculation by a simplified plane multibody model, but to show the mathematical correlation between rotor dynamics, electromagnetic influence, oil film characteristics of the sleeve bearings, the influence of a soft foundation, and excitations by different kinds of rotor eccentricity, based on a simplified analytical model. Beside the absolute orbits of the rotor, stator, shaft journals, and bearing housings, also the relative orbits between rotor and stator and between shaft journals and bearing housings are mathematically described. In addition to these theoretical considerations, a numerical example for a soft mounted 2-pole induction motor is also shown. Finally, the paper shows the possibility of optimizing the system—electrical machine and foundation—regarding vibrations, caused by rotor eccentricities.     

再入系统的热流分析

针对再入过程中返回舱体存在严重的气动热问题,提出一种新型再入系统.通过建立减速系统的阻力估算模型和求解动力学方程,分析再入过程的速度特性和驻点热流密度,计算结果与文献算例数据吻合,验证飞行器再入过程的热流特性.采用Euler数值计算与边界层内工程算法相结合的方法计算充气阻力罩表面热流密度,结果表明热流密度在驻点附近较大,远离驻点后迅速减小.     

Parallel CFD simulations of an original and redesigned hydraulic turbine draft tube

The design of hydraulic turbine draft tubes has traditionally been based on simplified analytic methods, model and full-scale experiments. In the recent years the use of numerical methods such as computational fluid dynamics (CFD) has increased in the design process, due to the rapid escalation in computer performance. Today with parallel computer architectures, new aspects of flow can be considered. However, several problems have still to be solved before CFD can routinely be applied in product development. This paper aims to investigate the parallel performance of commercial CFD software on homogeneous computer networks, as common solutions encountered in the industry today. In addition, the efficiency improvements obtained in earlier experiments by modifying the shape of the draft tube will be considered, to deduce if the improvements can be captured with aid of CFD. Results from both the steady and the unsteady CFD simulations show that almost full scalability is obtained with the commercial CFD software CFX-5.7.1. Furthermore, no noticeable improvement in the pressure recovery factor or the flow field is noticed in the CFD simulations as compared to experiments. The discrepancy may be to the applied inlet boundary conditions and/or the turbulence model.