液力透平蜗壳内非定常压力脉动的研究

液力透平内部流场的非定常压力脉动是影响机组运行稳定性的关键因素之一,为了研究液力透平蜗壳内部的压力脉动,采用流场分析软件对一单级液力透平内部流场进行了三维定常和非定常数值模拟,对蜗壳流道内不同周向位置、径向位置和不同流量时的压力脉动进行了时域和频域分析。结果表明:在一个叶轮旋转周期内蜗壳内压力的脉动数量等于叶片数;蜗壳入口位置和割舍位置处压力脉动较小,蜗壳环形部分中部和割舍前端位置处压力脉动较大;蜗壳内压力脉动的主频和次主频分别为叶频和2倍叶频;液力透平蜗壳内部的压力脉动程度在小流量下较小,随着流量的增加,压力脉动程度逐渐增加,大流量时最为剧烈。为了验证数值计算的准确性,建设了开式液力透平试验台,制造了模型样机对液力透平进行了外特性试验和非定常压力脉动测量,验证了数值计算的准确性。     

离心泵叶轮内非定常流动的动态模态分解分析

为了精确分析离心泵叶轮内复杂的非稳态流动特性,基于泵内流动的大涡模拟(large eddy simulation, LES)数值计算结果,在设计工况及小流量工况下对叶轮内非定常相对速度场进行动态模态分解(dynamic modal decomposition, DMD),得到能够反映叶轮内复杂流动特征的前4阶主要模态及其相应的频率信息。分析结果表明：DMD方法能够有效识别叶轮内复杂流动的脉动频率,提取出相应的流场结构,将叶轮内复杂的流场特征分解为基本模态特征、反映叶轮流道内流动分离及不稳定涡结构的高阶动态模态特征;基本模态能够反映由流道几何形状引起的叶轮出口高速射流区与低速尾迹区及叶片背面流动分离区域。设计工况速度场2阶～4阶动态模态流场反映出叶轮内流动受蜗壳干扰在叶片背面产生的流动分离及不稳定涡结构脱落特征;小流量工况速度场动态模态表征了由于叶轮旋转及蜗壳干扰在流道内发生流动分离、失速等流场特征。通过DMD方法能够有效地对叶轮内重要流场结构进行低维近似,清楚地分析离心泵叶轮内复杂流场的非定常特性。     

对旋风机级间流场涡量和噪声分布规律的分析

利用LES（大涡模拟）方法对一台对旋风机进行全流场非定常的模拟计算,获得风机内部流场的数值模拟数据。在对旋风机级间流场设置若干监测面,并在监测面的轮毂、流道和机壳位置分别设置监测点,并将对旋风机两级叶轮中间区域的涡量分布情况进行分析,研究对旋风机两级叶轮中间流场涡量分布的特点;利用FW-H噪声模型对对旋风机气动噪声分布情况进行模拟;研究涡量分布与风机噪声特性之间的关系。研究结果可为对旋风机气动噪声分析提供参考。     

核主泵小流量工况压力脉动特性

为研究小流量工况下核主泵内部压力脉动的变化规律,基于雷诺时均N-S方程和标准k-ε两方程及SIMPLEC算法,应用CFX软件对核主泵小流量工况进行定常和非定常数值计算,得到泵内部流场和各工况监测点的压力脉动,并将时域信号进行快速傅里叶变换为频域信号。结果表明:核主泵内压力脉动明显,叶频在由压力脉动诱发的振动中起主导作用,主要表现为叶轮和导叶间的动静干涉。叶轮导叶流道内的回流造成了小流量工况叶轮和导叶流道及其周向的不稳定压力脉动,回流主要存在于叶轮和导叶进出口位置,因此该区域的压力波动剧烈且周期性差。核主泵的振动,不利于核电站的安全稳定运行,通过对小流量工况的压力脉动分析,对预测核主泵在极端工况下的动态特性和推进核主泵国产化具有十分重要的意义。     

大流量工况下核主泵内部不稳定特性分析

为了研究大流量工况下,核主泵内部流动不稳定特性,基于RNG k-ε湍流模型,利用ANSYS CFX对大流量工况下核主泵内部流场进行三维非定常数值模拟,分析了大流量工况下在导叶不同位置9个监测点上压力脉动的时域和频域特性。研究结果表明:由于漩涡的存在,H~Q曲线在1.0Qd~1.1Qd内出现正斜率现象。核主泵导叶流道内最大压力脉动出现在导叶进口处,随着流量的变化,主泵运行偏离最优工况越远,导叶进口处的压力脉动系数越大,在1.3 Qd工况时导叶进口处的压力脉动系数最大且为出口处的2.5倍;蜗壳壁面的径向力受流量变化影响最大,在一个旋转周期内蜗壳壁面所受到的径向力随流量的增加平均值逐渐增大,偏离额定工况越大,蜗壳壁面受到的径向力最大,导叶次之,叶轮最小。试验与数值对比分析发现大流量工况下二者吻合较好,证明该数值模型可较准确地描述泵内流场特征。     

自吸离心泵叶轮内流场的数值模拟

本文基于N—S方程和标准κ-ε紊流模型,对ZBY80-35／45自吸离心泵叶轮设计流量下叶轮内流场三维紊流进行了数值计算,获得了叶轮内流场的速度、压力分布,对数值计算结果进行了分析研究,为叶轮的水力设计提供了有价值的信息。     

组合压气机中尾迹与势流同频/异频干涉的叠加特性

为揭示多级压气机中上下游叶轮对中间叶片叠加气动影响特性,阐述不同叠加干涉情况下下游叶轮进气角度变化,采用数值方法模拟了一级轴流和一级离心组成的组合压气机非定常流场。详细讨论了上游动叶尾迹和下游动叶势流对中间导流叶栅段气流非定常流动的异频和同频叠加干涉特性,依据计算结果,直观地展示了静叶通道中两种干涉间相互激励和抑制作用的位置和时间,与数学公式的推导结果相互印证。研究结果表明:当上下游动叶对中间静叶段异频干涉时,干涉的激励、抑制区域的轴向位置随时间发生变化;当上下游动叶对中间静叶干涉频率相同时,干涉的相互激励、抑制区域的轴向位置不随时间发生变化,但干涉的激励、抑制区域的轴向位置受时序位置影响。另外,上游动叶尾迹与下游离心叶轮势流的不同叠加情况,决定着下游离心叶轮进口相对气流角的大小及波动幅值。      

气体涡轮流量计流道压力损失的数值模拟

采用计算流体力学(CFD)的方法对一口径为80mm的气体涡轮流量计进行工况条件的数值模拟研究.通过计算,分析了流量计在不同流量下,各部件包括前整流器、前导流器、机芯壳体、叶轮支座、叶轮和后导流器对压力损失的影响,给出了各部件的流量与压力损失的关系曲线及其压力损失比例.数值模拟结果与实验结果相符,进而从流道内的压力分布和流场分析压力损失原因并提出减少压力损失的改进思路.     

离心泵变工况过渡过程瞬态水力特性研究

为研究离心泵汽从设计工况向非设计工况过渡过程的瞬态水力特性及内部流动机理,通过pro/E软件对离心泵内部流道进行三维造型,利用雷诺时均N-S方程和 两方程及SIMPLEC算法,应用计算流体力学软件CFX对离心泵叶轮流道内的变工况瞬态流动特性进行数值模拟计算,研究分析离心泵在进口压力连续下降时其内部的汽蚀特性进行数值模拟,并与试验结果进行对比, 结果表明：数值模拟结果与试验结果的变化趋势一致。流场分析表明：变流量过渡时,叶轮流道内的压力值没有明显增大,但压力变化幅度随流量的变化而增大;向大流量过渡时,流量增加对叶片瞬态载荷影响不大,而向小流量过渡时,由于二次回流等因素的存在对叶片瞬态载荷影响很大;由设计工况向汽蚀工况的过渡过程中,在临界汽蚀余量时,受到气泡相的影响叶片的瞬态载荷变化较大,特别是进口处叶片载荷瞬态变化更大;压力值与其幅度都出现急剧下降;作用在叶轮上的径向力大小和方向也急剧增大。     

换气扇内部流场的数值仿真和能效分析研究

某种型号换气扇(B型)在使用中,存在能效偏低的问题,应用计算流体力学方法对其三维内部流场进行了数值模拟,预测了最大风量和整体能效曲线,通过与试验数据比较表明了数值计算的可靠性.进而详细分析了换气扇子午平面和回转面的流动情况,出风口与叶轮之间的间隙流动及叶轮流道内的二次流等局部流动特征.上述结果对于对该换气扇进行优化设计和改型有一定的指导和借鉴意义.     

运行参数与轴流泵流体激励力的关系

泵内非定常压力脉动会引发泵体的结构振动,运行工况的变化会改变泵内流场的流动状态,从而对泵的振动特性产生影响。通过流体力学计算软件FLUENT对某台立式轴流泵内流场进行仿真计算,分别改变泵运行速度和流量两项参数,得出转速改变后,叶轮受到的力会偏离了相似理论的计算值;工作在小流量时,泵内压力脉动与叶轮受力均大于大流量工况,且叶轮区域出现流动分离现象,不利于振动噪声的控制。     

Unsteady flow investigation in rotor-stator interface of a radial diffuser pump

The flow in a vaned diffuser radial pump is fully turbulent and strongly unsteady, caused by the rotor-stator interaction. In this paper, two-dimensional laser Doppler velocimetry (LDV) measurement results have been utilized to investigate the unsteady flow in a low specific speed radial diffuser pump with leaning impeller trailing edges. CFD simulations have been also conducted to provide more extensive results at different flow rates. The analysis has been mainly focused on the flow in the radial gap region between the impeller and diffuser where the unsteady interaction is the strongest. The velocity and turbulence fields are detailedly examined and quantitatively compared between CFD and LDV as well. In addition, the downstream effect from the impeller rotation has been compared between the leaning and normal trailing edges of the impeller.     

Druckschwingungsverteilung im Seitenkanal von Verdichtern

Distribution of the pressure oszillations in the side channel of compressors The investigation of the unsteady pressure field in side channel machines with high pressure coefficients of ψ_n = 3,5 to 34 gives a better understanding of the unsteady turbulent vorticity flow in the impeller and the side channel and also of the energy transfer. The impeller with high number of blades generates a turbulent vorticity flow, which exists over the entire side channel. The specific momentum causes pressure oscillations of p(t) = 250 Pa to 9,0 kPa also in the entire side channel which lead to an increase of the static pressure in the circumference of the side channel. The oscillation of the pressure is exited by the blade passage frequency and the frequency of the turbulent vorticity flow, with the lower frequencies having priority to the energy transfer. It also leads to dissipation losses limiting the efficiency and causing a heat up of the gas.     

Dämpfung von Rotating Stall in Radialverdichterstufen

In part load span centrifugal compressors incline rotating stall in the impeller, which often causes transient pressure oscillations and surge. Operation in part load span with transient processes has to be avoided, because it can endanger the compressor and the plant by vibrations. Active devices like an upstream or downstream side channel stage can influence flow and unsteady gas pressure oscillations in centrifugal compressor stages and shift rotating stall to lower flow or entirely avoid it. This article shows experimental results for characteristic lines and unsteady gas pressure oscillations in centrifugal compressor stages, which where coupled with an downstream side channel stage. The enforced turbulent eddy flow with unsteady gas pressure oscillation in side channel stages diminishes unsteady gas pressure oscillation in the centrifugal compressor stage and limits pressure gradient as well as the maximum reachable value of gas pressure oscillation at rotating stall.     

有气相注入的管内气液分层流数值模拟

管内气液两相分层流是管道输运和水平井采油过程中重要的研究课题之一，而气液界面是研究的重点内容，尤其是有气泡穿过界面的分层流是水平井采油过程中从有壁面注入时不可回避的流动现象，也是数值计算的难点所在。本文利用VOF方法[1]捕捉气液界面，应用有限体积方法和重正化 湍流模式[2]计算圆管内三维非定常雷诺平均方程，得到了典型的界面上有质量交换时的分层流的流场、界面形状和界面上阻力变化的结果。     

某跨音速高压涡轮非定常流动数值模拟研究

通过求解三维非定常雷诺平均N-S方程模拟某跨音速高压涡轮非定常流场,研究涡轮内非定常流动特征。通过对静子尾迹及静子尾缘激波和转子叶排之间的相互干涉过程进行详细分析,发现定常/非定常模拟方法获得的涡轮总体性能参数基本一致但流场存在较大差异。静子尾迹是导致涡轮流场非定常性的重要因素之一:在转子叶栅通道中部和下部,静子尾迹和转子叶片附面层及下通道涡发生明显干涉,并导致通道中下部损失周期性波动幅度较大,此外尾迹和下通道涡间的干涉作用在转子尾缘处诱导出高频脱落涡。静子尾缘激波也是导致涡轮流场非定常性的原因之一,激波和转子叶片作用形成复杂的波系结构,对涡轮流场影响显著:一方面激波/附面层干涉导致转子和静子的吸力面产生周期性变化的高温区域;另一方面激波撞击叶片导致叶片表面的气流在激波后出现分离,对转子静压分布产生影响,使得转子叶片表面载荷出现明显的非定常性,进而导致涡轮输出功的周期性波动十分剧烈。     

空调离心叶轮尾流噪声的数值预估

由于现有的计算技术限制,风机气动噪声的数值预估是非常困难的。对于单个离心叶轮,已知其最主要的气动噪声源是叶片尾缘涡脱落导致的叶片表面压力脉动。基于Lee(1993)的轴流风机尾流噪声模型,提出一种可适用于离心叶轮尾流噪声数值预估方法。它包括三项主要工作:首先利用商用CFD软件Fluent对叶轮内的三维流场进行了数值模拟,并对所得气动性能进行实验验证;然后对叶片尾缘附近的速度剖面进行分析,提取出吸力面和压力面两侧的边界层厚度;最后,根据改进的噪声预估模型对叶轮的总声压级进行数值预估,在设计工况附近所得结果与实验值相比误差小于3dB。     

侧壁式压水室离心泵小流量非稳态旋转失速特性

用数值计算方法研究具有特殊结构的侧壁式压水室离心泵,分析小流量工况时模型泵的非稳态旋转失速特性,用快速傅里叶变换(FFT)获得压力脉动信号的频谱特征。结果表明,小流量工况时模型泵的扬程曲线呈驼峰状,压水室不同位置处压力分布不均;受叶轮旋转产生的非稳态作用影响,叶轮不同叶片流道内流动结构差异较大。不同流量下,叶轮内部分离涡结构诱发的激励频率各异,0.4ФN工况时模型泵压力脉动频谱图出现0.5fR及高次谐波频率,压力脉动最大幅值出现于4fR频率处;0.2ФN流量时非定常流动结构会诱发0.18fR及高次谐波频率;0.05ФN流量时压力脉动频谱图同时出现0.1fR、0.28fR两种激励频率。旋转失速现象出现时,频谱图中叶频处压力脉动幅值不再起主导作用。     

Überschallströmung und instationäre Verdichtungsstöße in Seitenkanalverdichtern

For some years it is known that the admission flow into the side of side channel compressors sensitive and thereby disrupt the work of transferring gas to the impeller only to the scope angle of Δα _K =95° begins. The delay of the work transferred to the breaker could exit through the stationary pressure measurement in the side channel in 1999 identified and confirmed repeatedly. The reason, however, could not be found so far. Only the unsteady pressure measurement in the rotating impeller and a strong temporal resolution of the pressure in the breaker and behind the breaker showed unsteady compression shocks immediately after the interrupter input and output. The following contribution shows the experimental results of pressure measurement in rotating impeller. The results were measured by a telemetry system with transmitters and receiving antenna from the rotating impeller in the high-resolution measurement has been transferred. This allowed the foundations for a further optimization of the side channel and transmission of the work to be.     

A FINITE ELEMENT PERTURBATION METHOD FOR COMPUTING FLUID-INDUCED FORCES ON A CENTRIFUGAL IMPELLER ROTATING AND WHIRLING IN A VOLUTE CASING

A finite element based method has been developed for computing time-averaged fluid-induced radial excitation forces and rotor dynamic forces on a two-dimensional centrifugal impeller rotating and whirling in a volute casing. In this method potential flow theory is used, which implies the assumption of irrotational inviscid flow. In comparison with other analyses of fluid-induced impeller forces, two main features have been included. Firstly, the hydrodynamic interaction between impeller and volute isproperly modelled. Secondly, the variation of the width of the volute has been adequately included in the two-dimensional analysis by a modification of the equation of continuity. A regular perturbation method is used to deal with the effects of the whirling motion of the impeller. The excitation forces are calculated from the zeroth-order problem in which the impeller axis is placed at the volute origin. The rotor dynamic forces associated with the whirling motion of the impeller are derived from the first-order solution. The force components, tangential and normal to the whirl orbit, are predicted as functions of the impeller--volute geometry, the flow conditions and the whirl speed ratio. The method is applied to a centrifugal pump experimentally tested at the California Institute of Technology. Comparisons between predictions and experimental data show the capabilities of the proposed method to reproduce the main features of fluid-induced impeller forces in centrifugal pumps. © 1997 by John Wiley & Sons, Ltd.