可逆式水轮机变工况研究

针对抽水蓄能电站稳定性的要求,利用可逆式水轮机水泵工况断电过程中蜗壳出水边的压力始终保持恒定（水轮机工况的水头）,机组转速连续变化这一规律,根据转速的不同来选取不同的工况点。在Fluent软件中,通过变换转轮的边界条件设置,可模拟可逆式水轮机水泵断电过程不同工况点水力变化,计算时采用雷诺时均方程和RNG肛￡湍流模型,压力和速度耦合采用半隐式（SIMPLEC）算法。对可逆式水轮机不同工况点模拟结果进行了分析总结,数值试验结果直观地反映了可逆式水轮机水泵工况断电的不同工况点、叶片表面的压力分布、蜗壳内部的流场漩涡分布、水力损失等,对可逆式水轮机的转轮设计和结构优化有一定的应用价值。     

Analysis of transient flow in a pump-turbine during the load rejection process

The transient flow in pump-turbines during the load rejection process is very complex. However, few studies have been conducted on three-dimensional (3-D) numerical simulation. Hence, we simulated 3-D transient turbulent flow in a pump-turbine during the load rejection process using the calculation method of coupling the flow with the rotor motion of rigid body. To simulate the unsteady boundary conditions, the dynamic closing process of the guide vanes was simulated with the dynamic mesh technology. The boundary conditions at the spiral-casing inlet and the draft tube outlet were determined using the user defined functions (UDF) according to the experimental data. The numerical results of the rotational speeds show a good agreement with the experimental data. Then, the complex transient flow in the pump-turbine during the load rejection process was analyzed based on the numerical results. The results show that there are severe unsteady vortex flows in the vaneless space near the conditions under which the hydraulic torque on the runner equals to zero. When the pump-turbine operates into the maximum reverse discharge condition in the reverse pump operating process, the unsteady vortex flows in the vaneless space are instantaneously impacted into the region between the guide vanes and the stay vanes by the sudden reverse flows. The formation and development mechanism of the unsteady vortex flow in the vaneless space is associated with the distribution characteristic of the velocity field.     

Experimental study on hydrodynamic performance of a cavitating centrifugal pump during transient operation

An experimental study has been carried out in order to analyze the cavitation of a centrifugal pump and its effect on transient hydrodynamic performance during transient operation. The transient characteristics of the centrifugal pump were tested under various suction pressure and starting conditions. In transient operation of continuous starting and stopping process, instantaneous rotational speed, head, flow rate and suction pressure of the pump were measured. The effect of cavitation on transient performance of the centrifugal pump during transient operation was analyzed, and then the effects of starting acceleration rate and suction pressure of pump on cavitation were presented. Results showed that the cavitation would be delayed during rapid starting period. However, in the condition of low suction pressure and high rotational speed, pump cavitation is inescapable even if the starting period is less than a second. After the serious transient cavitation occurred, the transient performance of centrifugal pump would decline obviously, and the instantaneous head of pump would fluctuate.     

双向轴流泵装置性能预测与内部流动分析

对一采用S形叶片的双向轴流泵装置进行数值研究,在不同流量工况条件下分析泵的正、反向运转性能,对该泵的瞬时启动过程进行了监测并对泵内的非定常空化现象进行了分析。研究表明,正、反向运转时,泵的性能存在明显的差异,反向的扬程和效率均高于正向;在泵正向启动过程中,叶轮背面进口边产生空化区,反向运转时未发生明显的空化现象;两种运转模式下,叶轮进出口断面上压力脉动特征频率分布相似,但叶轮进口的压力脉动幅值较高。     

Analysis of the Pump-turbine S Characteristics Using the Detached Eddy Simulation Method

Current research on pump-turbine units is focused on the unstable operation at off-design conditions, with the characteristic curves in generating mode being S-shaped. Unlike in the traditional water turbines, pump-turbine operation along the S-shaped curve can lead to difficulties during load rejection with unusual increases in the water pressure, which leads to machine vibrations. This paper describes both model tests and numerical simulations. A reduced scale model of a low specific speed pump-turbine was used for the performance tests, with comparisons to computational fluid dynamics(CFD) results. Predictions using the detached eddy simulation(DES) turbulence model, which is a combined Reynolds averaged Naviers-Stokes(RANS) and large eddy simulation(LES) model, are compared with the two-equation turbulence mode results. The external characteristics as well as the internal flow are for various guide vane openings to understand the unsteady flow along the so called S characteristics of a pump-turbine. Comparison of the experimental data with the CFD results for various conditions and times shows that DES model gives better agreement with experimental data than the two-equation turbulence model. For low flow conditions, the centrifugal forces and the large incident angle create large vortices between the guide vanes and the runner inlet in the runner passage, which is the main factor leading to the S-shaped characteristics. The turbulence model used here gives more accurate simulations of the internal flow characteristics of the pump-turbine and a more detailed force analysis which shows the mechanisms controlling of the S characteristics.     

贯流泵装置模型试验转轮出水口压力脉动研究

结合某贯流泵装置模型试验,研究了转轮出水口的压力脉动情况.研究表明,转轮出水口压力脉动的统计参数绝对值随着扬程的提高而增大,相对值在最优效率区时最小;出水口存在与转频相关的脉动.一定叶片角度,不同扬程下,当流量小于该角度下最高效率点的流量时,出水口出现低频压力脉动,脉动表现为某个低频及其倍频.     

反转泵液力透平速度滑移机理

速度滑移对液力透平的水力性能和内流特性有一定影响。以反转泵液力透平为研究对象,评估不同湍流模型对液力透平水力性能影响的敏感性,通过数值模拟与试验值误差分析发现,采用RNG k-ε湍流模型预测液力透平水力性能具有较高的可信度。选用RNG k-ε湍流模型和CFX17.0,分析透平内速度滑移机理及速度滑移量化指标,进一步对比液力透平和离心泵速度滑移的大小及流动机理。研究发现：液力透平叶轮内存在速度滑移现象,速度滑移导致透平水头降低,并诱发了附着于叶片工作面的旋涡。透平滑移系数随比转速变化而变化,数值在0.2～0.4。比较反转泵液力透平透平工况与泵工况的滑移系数发现：当比转速大于50时,透平工况的滑移系数比泵工况的小,比转速低于50时,出现了透平工况滑移系数高于泵工况的情形。     

Computational analysis of centrifugal pump delivering solid-liquid two-phase flow during startup period

The transient behavior of centrifugal pumps during transient operating periods, such as startup and stopping, has drawn more and more attention recently because of urgent needs in engineering. Up to now, almost all the existing studies on this behavior are limited to using water as working fluid. The study on the transient behavior related to solid-liquid two-phase flow has not been seen yet. In order to explore the transient characteristics of a high specific-speed centrifugal pump during startup period delivering the pure water and solid-liquid two-phase flow, the transient flows inside the pump are numerically simulated using the dynamic mesh method. The variable rotational speed and flow rate with time obtained from experiment are best fitted as the function of time, and are written into computational fluid dynamics （CFD） code-FLUENT by using a user defined function. The predicted heads are compared with experimental results when pumping pure water. The results show that the difference in the transient performance during startup period is very obvious between water and solid-liquid two-phase flow during the later stage of startup process. Moreover, the time for the solid-liquid two-phase flow to achieve a stable condition is longer than that for water. The solid-liquid two-phase flow results in a higher impeller shaft power, a larger dynamic reaction force, a more violent fluctuation in pressure and a reduced stable pressure rise comparing with water. The research may be useful to tmderstanding on the transient behavior of a centrifugal pump under a solid-liquid two-phase flow during startup period.     

载荷扰动下滑动推力轴承绝热瞬态过程分析

分析了滑动推力轴承在载荷冲击下的绝热瞬态行为.通过对轴承油膜压力、温度及推力盘动力学建模,应用有限差分法以及Newton-Raphson法对模型求解,获得了大载荷扰动工况下滑动推力轴承热瞬态性能参数的非线性变化规律.讨论了载荷幅值,初始速度等对热瞬态过程的影响.结果表明,载荷冲击会在短时间内造成油膜温度显著升高及最小膜厚减小,从而导致轴承在瞬态过程中失效.     

并联液流通道结构的磁流变制动器电磁场和温度场特性分析

为了改善磁流变制动器的制动性能,提出一种并联液流通道结构的磁流变制动器.通过合理利用材料的导磁特性,使磁流变制动器内部的3层轴向阻尼间隙均被利用,有效提升了制动性能.建立了并联液流通道结构的磁流变制动器的力学模型,并对磁流变制动器进行了电磁场仿真分析;由仿真分析可知,磁流变制动器在转速为400 r/min时,最大制动转...     

后掠式轴流泵内部流场的二维PIV试验研究

以一后掠角为60°的后掠式轴流泵为研究对象,采用PIV技术对其内部流场进行测量,得到了0.8Qopt,1.0Qopt,1.2Qopt3个工况下叶轮在一个流道周期的12个拍摄截面上的速度场。发现在0.8Qopt工况下,经过后掠叶片的流体具有明显的径向流动趋势,流量越小径向流动趋势越明显。叶轮内流体在后掠叶片进口边和转轮端壁区容易出现低速区域,并且流量越小低速区域越大;在靠近轮缘附近,叶片进口边压力面上的流体会向吸力面流动,流量越小该现象越明显。研究结果对掌握不同型式叶片的轴流泵内部流动特性具有重要的理论指导作用。     

Gas-liquid flow patterns visualization in a self-priming centrifugal pump

The self-priming pumps are ubiquitous in gas-liquid mixtures lift and transportation areas. The fast self-priming time is a vital evaluation index for a self-priming pump. However, the bubble movement path and the bubble size distribution characteristics during the self-priming process are still an open issue. This paper aims to obtain the gas-liquid flow patterns inside a centrifugal pump during the self-priming process and evaluate the effect of the rotational speed and the position of the back-flow hole on the self-priming time through experiments. A centrifugal pump with a double-blade was designed as a visualization prototype. The high-speed photography technology was used to capture the bubble motion and size in the pump during the self-priming process. The bubble image processing method was used to identify the bubble size distribution in the diffuser during the self-priming process. The bubble number and size distribution images were presented to understand the influence of the rotational speed and the position of the back-flow hole. The higher rotational speed accelerates the gas-liquid mixing rate and shortens the self-priming time. However, there is a limited value of the self-priming time as the speed goes up to a certain high level. Moreover, the position of the back-flow hole slightly affects the self-priming time.     

混流泵起动过程转子轴心轨迹的试验研究*

混流泵起动过程中的振动失稳严重威胁着泵机组的安全,研究起动过程中的轴心轨迹,可以全面、直观地反映瞬态效应对机组运行稳定性的影响,掌握非调节工况下转子的振动状态。基于本特利408数据采集系统,测量获得了起动加速过程中不同转速下转子的轴心轨迹图和时域图,分解提纯一倍频和二倍频轴心轨迹图及其时域图,解析起动过程不同转速下的频谱图。研究结果表明,加速过程中,一倍频轴心轨迹由长短轴相差不大的椭圆逐渐变为圆形,可以判断转子存在弓状回转涡动且涡动不断加剧;二倍频轴心轨迹由近似水平线段逐渐变化为水平方向扁平的椭圆,可以判断转子存在不对中现象且水平方向的振动不断加剧。结合瞬态外特性曲线,研究发现随着转速的逐渐增大,转子系统的瞬时水力冲击逐渐增大,转子不平衡量和径向偏移量逐渐增大,振动情况逐渐加重,当转速达到最大值时,轴系振动出现一个峰值并随转速稳定有所降低并逐渐趋于稳定。加速是引起轴系振动的主要原因,瞬态效应是影响振动故障恶化的重要因素。研究成果对于实时评估混流泵起动过程中的轴系运行状态、有效降低或防止振动故障的恶化具有重要的工程应用价值和理论指导作用。     

混流泵停机过程的瞬态水力特性分析研究

针对混流泵在不同转速下停机过程中的瞬态水力特性进行了试验研究，并对试验结果进行了讨论。介绍了用于瞬态水力性能测试的试验设备以及试验方法，不同转速下停机过程的瞬态水力特性，并尝试用三次多项式拟合的方法模拟停机过程的流量-扬程曲线。试验结果显示了在停机瞬间泵的流量和扬程迅速下降，管路能量亦急剧降低，但在这一过程中无噪音和气泡产生，由此提出了瞬态工作泵的停机阶段操作方法。同时，试验结果亦显示了三次多项式拟合曲线与实际测量曲线能基本符合。试验和计算结果可在瞬态工作特性方面为瞬态离心式水泵的设计和实际使用打下基础。     

变转速工况对直线共轭内啮合齿轮泵容积效率的影响

随着液压技术向高压化、轻量化、节能化发展,直线共轭内啮合齿轮泵因具有结构紧凑、流量脉动小、使用寿命长、噪声小等优点,其应用领域逐步扩大。随着内啮合齿轮泵使用转速的变化,其容积效率也出现变化,为了获得内啮合齿轮泵转速对其容积效率的影响规律,采用液压油、纯水两种介质,通过数值计算的方法,研究内啮合齿轮泵转子域空化特性、对比分析出口体积流率。结果表明：随着转速上升,内外齿啮合最小容积腔及吸油口处气相体积分数增加明显,易引起空化、气蚀,从而产生噪声、振动等问题;当转速过高时,介质中的气体析出明显,易出现吸空现象,导致齿轮泵容积效率降低,纯水介质比46#液压油介质下的齿轮泵容积效率更低。因此,要改善高转速工况下的齿轮泵容积效率,需优化内啮合齿轮泵进油口流道,增加入口压力,提升内啮合齿轮泵高转速工况下的综合性能。     

Centrifugal pump transient characteristics and analysis using the method of characteristics

A theoretical and experimental study has been carried out on the transient characteristics of a centrifugal pump during starting and stopping periods. Experiments have been conducted on a volute pump with different valve openings to study the dynamic behaviour of the pump during normal start up and stopping, when a small length of discharge pipe line is connected to discharge flange of the pump. Similar experiments have also been conducted when the test pump was part of a hydraulic system to study the system effect on the transient characteristics. Instantaneous rotational speed, flowrate, and delivery and suction pressures of the pump are recorded and it is observed in all the tested cases that the change of pump behaviour during the transient period is quasi-steady. The dynamic characteristics of the pump have been analysed by a numerical model using the method of characteristics. The model is presented and the results are compared with the experimental data. As the model contains speed acceleration and unsteady discharge terms, the model can be applied for analyses of purely unsteady cases where the pump dynamic characteristics show considerable departure from their steady-state characteristics.     

新月形内齿轮泵空化流场仿真分析

实际液压系统工作条件一直处于动态演变过程。为了分析变工况后新月形内齿轮泵空化流场的演进规律,提出了一种分布式参数模型,该模型利用动网格技术及两相流模型相结合来模拟齿轮泵中含气油液的流动状况。根据因子水平表及正交表性质设计了正交试验方案,在此基础上计算了不同试验对应的三维内流道模型并获得了流场特性及空化演进规律。结果表明:该类型齿轮泵中无明显困油区域,转子区是整个泵内压力最高也是最低的区域;转速一定时,油温对最低压力的影响最大,含气量次之,工作压力的影响可忽略;啮合区中的空化演进规律最为明显,气相整体呈现出先均匀分布,再分散集中,最后又均衡分布的变化规律;压力演变是气相发生运移的根本原因。     

Application of the Modified nverse Design Method in the Optimization of the Runner Blade of a Mixed-Flow Pump

To improve the design speed and reduce the design cost for the previous blade design method, a modified inverse design method is presented. In the new method, after a series of physical and mathematical simplifications, a sail?like constrained area is proposed, which can be used to configure di erent runner blade shapes. Then, the new method is applied to redesign and optimize the runner blade of the scale core component of the 1400?MW canned nuclear coolant pump in an established multi?optimization system compromising the Computational Fluid Dynamics(CFD) analysis, the Response Surface Methodology(RSM) and the Non?dominated Sorting Genetic Algorithm?II(NSGA?II). After the execution of the optimization procedure, three optimal samples were ultimately obtained. Then, through comparative analysis using the target runner blade, it was found that the maximum e ciency improvement reached 1.6%, while the head improvement was about 10%. Overall, a promising runner blade inverse design method which will benefit the hydraulic design of the mixed?flow pump has been proposed.     

梯形卸荷槽对外啮合齿轮泵困油压力与流量脉动影响的研究

为减小“困油”所引起的压力冲击与流量脉动,基于双斜型卸荷槽、根据齿轮的啮合特点以及啮合过程中困油腔容积的变化规律,对原耳形卸荷槽进行优化,设计了一种具有更大卸荷面积、结构更加紧凑且易加工的梯形卸荷槽。在数值模拟过程中,分别监测耳形、梯形卸荷槽所在的齿轮泵流场困油区压力与出油口流量变化情况。结果表明:当转速在1000~4000 r/min内变化时,梯形卸荷槽能使困油容积区域压力峰值比耳形卸荷槽分别降低36.3%~47.5%,10.7%~22.5%;能使出油口流量脉动系数降低20%~86.1%。证明了梯形卸荷槽降低困油压力缓解困油现象的高效性与降低泵出油口流量脉动的有效性,为渐开线外啮合齿轮泵卸荷槽的创新设计提供了一种新的途径。     

变转速工况下离心泵蜗舌处压力波动的试验研究

对某一单吸离心泵在变转速工况下蜗舌处的压力波动进行了测量与分析。该离心泵的叶轮为半开式叶轮并具有背叶片,它由原叶轮车削后得到,从而使得叶轮出口离蜗舌距离较大。结果显示:随着转速的提高,离心泵的流量及效率线性增大,而扬程以二次曲线形式增加。该离心泵蜗舌附近的压力波动频谱以叶轮转动频率整数倍的离散分量为主,特别是叶片通过频率及其二次谐波。最大波动分量的幅度占参考动压ρv22/2(v2为叶轮出口周向速度)的0.5%左右。随着转速的增大,压力波动的增加速度比转速提高速度快,且宽频波动幅度的提高比离散分量显著。另外,频谱分量中存在叶轮转动频率非整数倍的离散分量,以及与转速无关而取决于流体系统固有振动特性的离散分量。