基于流固耦合方法的水轮机蜗壳结构振动及损伤机理研究

蜗壳流道内的内水压力是引起外围混凝土发生损伤的主要原因.基于流固耦合理论,并引入混凝土弹塑性损伤模型,建立了流体与蜗壳结构耦合振动分析的理论框架,提出了一套水轮机流道内水体流动诱发蜗壳外围混凝土振动损伤的数值计算方法.首先基于有限体积法建立水轮机蜗壳流道流动的数值模型,同时采用有限元方法建立蜗壳结构固体区域的三维有限元模型;进而将流体区域边界上动水压力作为外荷载实时传递给固体区域边界进行三维有限元非线性损伤瞬态分析,实现了大型水轮机蜗壳结构中流体流场到固体应力、位移场的单向耦合三维数值分析.通过计算分析得到了水体流动诱发蜗壳外围混凝土振动的响应规律以及混凝土损伤的发展规律.     

离心压缩机蜗壳型线的一种二维逆命题计算方法

本文提出一个蜗壳型线的二维逆命题计算方法。该方法考虑了蜗壳进口流动参数沿圆周方向分布不均匀和蜗壳周向平面内损失分布的影响；改进蜗壳与叶轮或扩压器之间的匹配关系，改善离心压缩机和风机的性能，提高蜗壳的设计质量。     

离心风机蜗壳在内部流场脉动压力激励下的动力响应研究

数值模拟了离心风机蜗壳在非定常气动载荷下的动力响应.首先考虑蜗壳与轮盘轮盖之间的间隙及轮盖处的内泄露,模拟了T9-19No.4A离心通风机内部三维非定常流场.然后将作用在蜗壳表面的非定常气动力加载给蜗壳模型,并采用有限元方法对蜗壳进行动力响应计算,实现了从流体到结构的单向耦合.最后将实验测量和数值计算蜗壳的振幅进行对比,结果吻合良好,表明本文的方法能够较为准确地模拟蜗壳在内部流场脉动压力激励下的动力响应.     

垫层的E/d对水电站蜗壳结构的影响分析

利用ANSYS大型有限元软件,建立垫层蜗壳结构的三维有限元模型,研究了结构自重和内水压力作用下垫层弹性模量与厚度比值E/d对水电站蜗壳结构的影响,给出了蜗壳外围混凝土、蜗壳以及座环的特性随垫层E/d变化的规律。结果表明:在有垫层区,蜗壳外围混凝土承载比、与蜗壳接触处混凝土切向应力随垫层E/d增大而增大,蜗壳应力以及最大相对变形量随垫层E/d的增大而减小,当垫层E/d确定时蜗壳结构外围混凝土承载比、与蜗壳接触处混凝土切向应力、蜗壳和座环应力以及蜗壳变形量一定,不会随E或d的变化而变化;在无垫层区,蜗壳外围混凝土承载比、与蜗壳接触处混凝土切向应力、蜗壳应力变形与垫层E/d无关。     

蜗壳内紊流流场的有限元法计算

用有限元法计算径流式叶轮机械蜗壳的紊流时均流场.有关紊流模型采用K-ε两方程模型,用关于压力p的罚函数方法求解.所得结果可供分析蜗壳流场用.文中方法也可用于计算其他形状的二维通道流动.     

离心风机蜗壳振动辐射噪声的数值预测

数值模拟了T9-19No.4A离心风机蜗壳在非定常气动力作用下的蜗壳响应振动及其噪声.首先给出该风机运行时振动及噪声的测量结果,得出基频噪声是主要噪声类型.然后使用CFD软件ANSYS CFX对风机内部流场做了整场瞬态数值模拟.流体压力脉动作用于蜗壳产生一个随时间变化的力,激励其振动,实现流体到结构的单向耦合.接着运用ANSYS multiphysics模块对风机蜗壳进行了谐响应分析,最后应用LMS SYSNOISE模拟了蜗壳振动向外辐射的噪声.     

求解非定常空气动力学的分离变量法

本文使用分离变量法求解非定常流动。消去了时间变量，建立了三维和二维的非定常流动的分离变量以后的位势方程，作为算例计算了通风机蜗壳中的声场，得到了共鸣和不共鸣两种情况下的结果。     

洗扫车用离心风机气动噪声的优化

离心风机是洗扫车的关键部件,降低风机的气动噪声可极大提升产品性能。基于有限元分析软件和FW-H声比拟模型,对离心风机的气动噪声强度进行了计算。重点研究了蜗壳宽度和蜗舌半径两个结构参数对风机气动噪声的综合影响,结果表明:合理地减小蜗壳宽度和增大蜗舌半径能够在保持风机气动性能基本不变的情况下有效降低风机的气动噪声。基于数值分析软件,通过多项式拟合方法分别建立了蜗壳宽度和蜗舌半径与风机效率、全压以及总声压级之间的函数关系;并在不降低风机效率与全压的前提下,结合多目标优化遗传算法得到了最优的蜗壳宽度和蜗舌半径,优化之后风机的总声压级降低了2.8dB,降噪效果明显。     

非设计工况下离心式压气机蜗舌对蜗壳流场影响的计算与分析

本文介绍离心式压气机蜗壳在变工况下的非轴对称流场计算,着重分析蜗壳舌部对压气机特性的影响.在文献中介绍了偏离设计工况时蜗壳的非轴对称工作特性,文献对舌部进口条件作了修正,进而推广至变工况的场合.本文对文中所提出的舌部进口条件作了解析计算并考虑了粘性的影响.计算与实验表明,经舌部进入蜗壳的流量值对蜗壳的非轴对称流场起着相当重要的作用,它为改善压气机的特性提供了依据.     

变螺旋角方法离心风机蜗壳型线数值优化

基于变螺旋角蜗壳型线设计方法,通过大涡模拟(LES)计算风机内部的非定常流场,利用二次回归正交试验设计法,对某离心风机的蜗壳型线进行数值优化以降低风机的A声级。优化时以蜗壳型线起始和终了位置的螺旋角为设计变量,以非定常流场计算得出的时均效率和A声级为目标函数,通过优化得到使风机气动噪声最低的最佳螺旋角分布,进而得到最佳蜗壳型线。利用数值模拟对优化结果进行了验证,验证结果表明:优化之后,时均效率降低了0.07%,A声级降低了4.04dB,时均效率和A声级相对于原风机分别降低了0.09%和4.51%;本次二次回归正交试验优化具有较高的预测精度,与CFD数值验证得出的时均效率和A声级的相对误差分别为0.01%和0.53%。     

离心风机子午通道内湍流场数值模拟

由进风口－叶轮－无叶扩压器－蜗壳等部件组成的离心风机通道内流分析是非常复杂的，目前还只能是分别计算各部件内的流场，但必须考虑部件间的相互影响。本文采用轴对称Ｎ－Ｓ方程，根据三维叶轮通道计算给出的叶片力分布，求解了考虑叶片力的进风口－叶轮－无叶扩压器组成的子午通道问题，所得结果可用来给出三维叶轮通道计算的进口条件，并可用于优化设计进风口及叶轮前、后盘形状。该方法已得到实践检验。     

Application of the SAS turbulence model to predict the unsteady flow field behaviour in a forward centrifugal fan

In the current study, the unsteady flow in a centrifugal fan is carried out using Computational Fluid Dynamics calculation based on the Scale Adaptive Simulation (SAS) approach to model the turbulence phenomenon. The SAS concept is based on the introduction of the von Karman length scale into the turbulence scale equation. The information provided by the von Karman length scale allows SAS models to dynamically adjust to resolved structures in an Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulation, which results in a Large Eddy Simulation-like behaviour in unsteady regions of the flow field. At the same time, the model provides standard RANS capabilities in stable flow regions. The introduction of the von Karman length scale is based on the reformulation of Rottas's equation for the integral length scale. To validate the numerical results, the overall performances of the fan and the wall pressure fluctuations computed upon the volute casing surface are compared with the unsteady measured data.     

Exit-flow velocity survey of two single-tangential-inlet vaneless turbine volutes

The most cited analytical technique for designing turbine volutes is to assume the throughflow is free from torque, although for this assumption to hold, the volute walls must lie near what would be streamlines in an unbounded free vortex-plus-sink flow. The single tangential inlet design, with inlet offset decreased and diameter increased to attain the weak exit swirl required by high specific speed turbines, deviates from such a shape, and the volute’s internal geometry is no longer torque-free. It is desired to know the actual time-averaged flow leaving such a volute, so that a rotor can be designed to compliment it.For two existing single tangential inlet volutes, time-averaged radial and tangential velocity and static pressure measurements of exit flow have been obtained on a cylindrical cut plane through the radial-inflow section using a three-port yawmeter in air. The Reynolds numbers based on inlet pipe mean conditions, around 10⁵, are well into the fully-turbulent regime and on the order of comparable water turbines.A comprehensive map of time-averaged exit flow of both volutes is presented. The integrated values of gross angular momentum flux change and total pressure loss coefficient are tabulated. Circumferential variation of flowrate and swirl strength highlight unexpected differences in outlet flow between the two volute designs. Results are presented alongside corresponding numerical results from the commercial package Fluent (Fluent, Inc., Lebanon, NH, USA) using Reynolds stress, k-ω, and inviscid flow models.In both volutes, measured gross exit angular momentum flux was more than 1.7 times what the zero-torque assumption would predict when blindly applied to the volute as a whole. This discrepancy is attributed to significant turning near the volute’s inlet region leading to an updated view of what an appropriate control volume is when applying the zero-torque assumption. Additionally, variation of both radial and tangential velocity in both the circumferential and axial directions on the order of 15% of the mean value reveal that volute swirl characterization by a single measurement would have a significant associated uncertainty.     

Internal flow numerical simulation of a cross‐flow fan in refrigerant operating condition using user‐defined functions

In the paper, a cross‐flow fan in refrigerant operating condition is systematically simulated using user‐defined functions. Three‐dimensional simulations are acquired with Navier–Stokes equations coupled with k–ε turbulence model, and internal flow characteristics of an indoor split‐type air conditioner are obtained, which is mainly composed of cross‐flow fan and heat exchanger. It has systematically been simulated in the isothermal flow condition that the performance of cross‐flow fan may be reduced easily with dry or humid air, and in the refrigerant operating condition in which user‐defined functions are applied to the humid air, considered as a mixture of dry air and vapor. A density‐modulated function is adopted to deal with the condensation of the vapor at the heat‐transfer region approximately. The results show flow mechanism of the two gas‐phase flow, including phase‐vary process. The distribution of the parameters is not uniform at the inlet of the machine, the intensity and position of pressure and velocity vary along the axial direction of the fan, the distribution of vapor volume fraction and turbulent intensity in heat‐transfer region is obtained, and the external characteristic data of the indoor machine are obtained and analyzed. Compared with the experimental data, the calculated characteristic curves and designed parameters are on target. © British Crown Copyright 2010/MOD. Reproduced with permission. Published by John Wiley & Sons, Ltd.     

Flow and performance characteristics of twin-entry radial turbine under full and extreme partial admission conditions

This paper presents numerical and experimental investigation of the performance and internal flow field characteristics of twin-entry radial inflow turbines at full and extreme partial admission conditions. The turbine is tested on a turbocharger test facility, which was developed for small and medium size turbochargers. Experimental results show that the lowest efficiency corresponds to extreme conditions. Therefore, flow field analyzing is employed to consider these conditions. The flow pattern in the volute and impeller of a twin-entry turbine is analyzed using an in-house fully three-dimensional viscous flow solver. The computational performance results are compared with the experimental results and good agreement is found. The flow field at the outlet of the turbine is investigated using a five-hole pressure probe; the numerical results are also compared with experimental measurements at the outlet of the rotor. For the volute, results show that lowest entropy gain factor corresponds to the extreme conditions, particularly when shroud side entry is fully closed. At the inlet of the rotor for equal admission conditions, the incidence angle is mostly in the optimum values. However, large variation in the incidence angle is seen in the extreme conditions, which lead to larger incidence losses and consequently a lower efficiency. In addition, entropy distribution contours corresponding to the exit plane are considered. For full admission, the location of low entropy gain factor at this plane occupies a region near the shroud side of suction surface as well as near the hub side of the pressure surface that corresponds to a region of high absolute flow angle. However, for the extreme cases, the low entropy gain factor occupies a relatively larger region near the shroud side than full admission. So, higher loss generation is noted at the extreme cases. Moreover, this entropy gain factor region is increased when shroud side entry is fully closed.     

叶片与蜗舌耦合对离心风机性能和旋转噪声影响的数值研究

利用三维N-S方程和RNGk-ε湍流模型对离心风机内部的非定常粘性流场进行了数值模拟,分析了不同时刻叶片与蜗舌所处的不同相对位置对风机瞬时性能、叶轮出口流动以及对蜗舌处的静压分布和静压脉动的影响。同时指出,改进特定时刻叶片与蜗舌处于特定相对位置时风机的瞬时性能是提高风机总体性能的一条新的途径。此外,还尝试运用一种新的方法,即不用求解声场而直接依据非定常流场中的静压脉动分析了蜗舌处主要气动噪声源的位置及其成因。     

一种考虑薄壁散射效应的声学计算模型

采用薄壁边界元/FW-H理论混合方法建立了考虑薄壁声学散射效应的数值计算模型.这种声学计算模型可以预测存在薄壁如风扇机匣、蜗壳等条件下的声波的传播及散射问题.计算模型的建立主要包含噪声源的计算和声源的传播两方面:首先建立FW-H的频域方程,并采用计算流体力学方法计算流场,通过流场数据计算气动噪声源;然后采用薄壁面边界元法计算固壁对声波的散射,并计算声波在固壁散射后的声场分布.数值计算结果和实验结果及经典的叶轮机管道风扇噪声理论进行了对比,结果表明,这种计算模型与理论计算结果及实验结果吻合较好,可以准确的预测机匣壁的散射效应对声源传播的影响.     

Effect of inlet volute wrap angle on the flow field and performance of double inlet gas cyclones

In response to the divergent understanding of double inlet cyclone performance in the literature, the effect of inlet volute wrap angle on the performance and flow field of double inlet cyclone separator was studied by Computational Fluid Dynamic (CFD) method. The results showed that the inlet volute wrap angle can affect the comparison results of the single and double inlet gas cyclones with the same total inlet cross-sectional area and velocity. 0° and 90° volute double inlet improved the efficiency mainly by separating particles below 10 μm, while 180° volute double inlet had no separation advantage for any particles, so the symmetrical double inlet does not always improve the efficiency, and the appropriate inlet volute wrap angle should be selected according to the actual situation, otherwise, the expected performance requirements of the symmetrical double inlet cyclone cannot be achieved. Compared with the flow field, it is found that the inlet volute wrap angle changed the tangential velocity of the symmetrical double inlet cyclone separator, thus changing the performance.     

Isothermal velocity and turbulence measurements downstream of a model multilobed turbofan mixer

An isothermal experimental investigation of the three dimensional flow field downstream of a model multilobed turbofan forced mixer is presented. LDA measurements of the three mean velocities and corresponding turbulence intensities were obtained in the downstream duct where the turbine (primary) and fan (secondary) streams emerging from the lobes mix together. The flow development in the near field was quantified by measuring the cross plane velocities. These were found to consist of large radial flows, of order 15% of the mean axial velocities at the lobe inlet, with changing sign depending on location. The cross-plane flow is consistent with a large scale axial vortex pair (per lobe) which persists throughout the downstream duct and enhances mixing in this region. Turbulence generation and anisotropy of the turbulence structure were evident mainly in the shear layers formed as the fan and turbine streams emanated from the lobe trailing edge. Spatial uniformity in the mean and turbulent fields was measured as little as five heights downstream of the mixer exit, indicating the rapid mixing achievable in these systems.     

Experimental investigation of the interaction of two flows on the axial fan hollow blades by flow visualization and hot-wire anemometry

Experimental investigation of the interaction of internal flow with external flow around hollow airfoil NACA series in a low-speed wind tunnel was conducted and is presented in the paper. The region near the trailing edge of the hollow airfoil was studied in detail and measurements of velocity and turbulence intensities were performed with hot-wire anemometry. Determination of flow structure on the hollow airfoil was performed with computer-aided visualization. It can be concluded from the measurement analysis that higher values of velocities, lower turbulence intensities and a significant decrease of circulation effects on the suction side of the hollow blade were achieved, due to the introduction of internal flow. The results obtained on the hollow airfoil were applied on the rotating axial fan. Influence of the internal flow of the hollow blade on the flow field of the axial fan was studied. With the introduction of the internal flow a reduction of circulation effects on the fan hollow blade was achieved. Aerodynamic characteristic of the axial fan reached higher degree of total pressure difference and normalized efficiency through the entire fan working conditions.