导叶时序对多级液力透平压力脉动的影响

为研究导叶时序对多级液力透平性能的影响,以两级径流式液力透平为研究对象,建立以首级导叶周向位置为基准,依次将次级导叶周向旋转10°的5种时序方案。基于RNG k-ε湍流模型对不同导叶时序位置引起的内流瞬态特性进行了研究。结果表明：导叶时序对液力透平外特性曲线有一定影响,但对各过流部件压力脉动影响更为显著;各监测点处压力脉动主频幅值随着导叶交错角度的增大呈现出不同的规律,当交错角度为40°时液力透平内压力脉动降幅最大,首、次级叶轮出口和次级导叶过渡段主频幅值相比0°方案分别降低了11%,51%和16%;导叶时序对首、次级导叶出口压力脉动几乎无影响。     

混流泵内压力脉动测量与分析

以比转速为336的某导叶式混流泵为例,沿流体流动方向在泵进口、叶轮出口、导叶出口、泵出口4个位置设置监测点,对比了0.6Q_d、0.8Q_d、Q_d、1.2Q_d、1.4Q_d(Q_d为设计流量)5种工况下的压力脉动情况。结果表明,泵进口和泵出口压力脉动幅值较低,导叶进口处脉动幅值最高,且小流量工况较大流量工况脉动剧烈,小流量工况下,泵内运行不稳定,出现回流、漩涡等,引起复杂、无规律的压力脉动;各工况下,泵进口处在叶频到7倍轴频范围内均出现了较为紊乱的脉动;与设计工况相比,非设计工况的脉动情况更为复杂。     

叶轮进口边型线对两级离心泵空化及非定常流动特性的影响

针对叶片进口边型线对两级离心泵空化及内部非定常流动特性的影响,在保持泵体和其他几何参数不变的情况下,通过改变第一级叶轮叶片进口边曲率,计算了两级离心泵内的空化及非定常流动。获得了空化性能曲线、第一级叶轮流道内测点的压力脉动和第一级叶轮的受力情况。结果表明:进口边对临界空化余量、压力脉动和受力情况的影响不具有单调性,而是存在最优值;压力脉动的主导频率为15倍轴频,并且压力脉动出现高幅低频现象;轴向力和径向力的脉动主频分别为轴频和2倍叶频;径向力的波动幅值远小于空间x,y方向受力的波动幅值。     

径向导叶对高速离心泵非定常流动影响的分析

应用计算流体力学技术对带导叶与不带导叶高速离心泵的内部流场进行定常及非定常数值模拟,从而预测出带导叶与不带导叶两种方案下的外特性曲线走势情况。同时得到了流体流经关键位置时在不同工况下的压力脉动情况,并对相应的时域图及频域图进行了对比分析。结果表明,带有导叶的高速离心泵相比于无导叶离心泵扬程较高,扬程曲线更加平缓,同时在大流量工况下,高速离心泵效率更高也更稳定。从时域图分析,不同工况下两种方案中的高速离心泵压力脉动存在明显的周期性,其中带有导叶的高速离心泵在大流量工况下压力脉动幅值相对较小,不带导叶的高速离心泵在小流量下压力脉动幅值相对较小;从频域图分析看,两种方案中的高速泵都是在一倍叶频处存在较大峰值,即动静干涉作用是引起压力脉动的主要因素,同时通过对比,在不同工况下带有导叶的高速离心泵在二倍叶频处峰值较小,说明添加径向导叶对缓解动静干涉起到一定作用。通过比较不同方案下监测点压力脉动平均值及峰值曲线图,说明在高速泵中加装径向导叶可以有效地发挥扩压作用,降低液流速度,充分将速度能转化为压能。结合上述结论,可以得出带导叶高速离心泵适合在大流量高工况下运行,如消防灭火,石油化工,航空航天等领域。     

斜流泵压力脉动模型试验研究

为探究斜流泵叶轮进出口处压力脉动的分布规律,通过模型试验测量斜流泵在不同叶片安装角度及扬程下叶轮进出口的压力脉动,运用时域和频域分析法对比分析压力脉动。结果表明,当扬程低于额定扬程时,随着扬程增加,泵运行趋于稳定,压力脉动相对幅值逐渐减小,当扬程达到额定扬程后,压力脉动相对幅值达到恒定值;叶轮出口处离转轮位置较近,受叶片旋转作业的影响较大,导致出水流道处压力脉动相对幅值较进口处大;叶轮进口处压力脉动频率以3倍转频为主,2倍转频脉动干扰较明显;叶轮出口压力脉动较复杂,在6倍转频处波动最大,同时伴有低频脉动。研究成果可为斜流泵设计与管理提供理论依据。     

固液两相流对离心泵压力脉动特性的影响

为了研究含沙水流下径向式导叶离心泵内的压力脉动变化规律,采用大涡模拟和Mixture多相流模型相结合的数值模拟方法,并结合SIMPLEC算法,对输送固液两相流介质的径向式导叶离心泵进行了全流道三维非定常数值计算,并在叶轮与导叶交接面及蜗壳出口段处,将固液两相介质与清水介质时的计算结果进行对比分析。数值计算结果表明,离旋转轴越远处压力脉动幅值越小;导叶与蜗壳内叶频是压力脉动主要频率,且在1倍叶频处最大;导叶内压力脉动幅值均大于蜗壳内,且随着颗粒粒径的增大,压力脉动幅值逐渐减小;蜗壳隔舌处的压力脉动幅值大于蜗壳其他部位;在叶轮与导叶交接面处,清水介质时压力脉动幅值大于固液两相介质时,固液两相介质时脉动波形滞后于清水介质时0.003 5 s;蜗壳出口段,固液两相时压力脉动幅值均大于清水时。     

低比转速多级泵间隙尺寸改变对内部流场及其性能的影响

为研究低比转速多级泵间隙尺寸的改变对内流场及其性能的影响,应用CFX软件对带间隙模型泵进行数值模拟,设计了12个间隙组合模型,分析了泵的外特性、间隙泄漏量、叶轮出口与导叶进口速度压力的变化规律。结果表明,随着间隙尺寸的增加泵扬程和效率均有所下降;叶轮口环的泄漏来自遭到撞击改变方向的叶轮出口流体,导叶口环的泄漏来自次级叶轮进口的流体;间隙对泵的影响程度依次为叶轮口环导叶口环叶轮与导叶的运转间隙;叶轮出口流出的液体进入导叶时极大地阻断了叶轮泵腔之间与叶轮导叶轴向间隙的流体交换。数值模拟结果较估计值仍然偏高,数值模拟对单一模型的准确度有待商榷,说明多组模型对比十分必要。研究成果为进一步深入分析奠定了基础。     

三级轴流式油气混输泵内流场压力脉动特性

为研究轴流式油气混输泵含气工况级间相互影响以及流道内压力脉动特性,应用Fluent软件数值模拟了三级油气混输泵在设计流量下的全流场瞬态,获得了混输泵内两相运动特征和流动部件内压力脉动情况,并分析了压力脉动时域和频域。结果表明,动静干涉是产生静压波动的主要因素,静压波动均值从入口到出口逐渐增大,级内动静交界处耦合作用较小,级间动静交界处耦合作用则较为明显。各级压缩单元叶轮进口均为脉动最剧烈的地方,距离叶轮进口越远,压力脉动幅值越小,在叶轮出口达到最小。在压缩单元内,流动方向的压力脉动主频幅值逐渐降低。首级叶轮出口、二级叶轮中间和出口以及末级叶轮中间位置压力脉动频率主要为2倍叶频,其他监测点压力脉动频率均为1倍叶频。气相对压力脉动频率影响较小,仅影响幅值。研究结果可为混输泵的结构优化设计及流动诱导振动控制提供参考。     

五级导叶式离心泵轴心轨迹的试验测量

鉴于多级离心泵轴心轨迹研究较少的问题,对五级导叶式离心泵的能量性能和轴心轨迹进行了试验测量。结果表明,设计工况下五级导叶式离心泵的扬程为165.40m、效率为72.84%;测点的轴心轨迹时域在x向呈现周期性的畸形正弦波,在y向呈现周期性的畸形余弦波;前轴承测点A1的轴振变化幅度大于后轴承测点A2的轴振变化幅度,前轴承B2的振动比后轴承B1的振动更强;设计工况下,前轴承测点A1的轴心轨迹呈现近似八字形分布,后轴承测点A2的轴心轨迹呈现近似椭圆分布。研究成果可为多级离心泵的振动特性分析提供参考。     

蜗壳进口宽度对离心泵非定常性能的影响研究

为分析蜗壳进口宽度对离心泵非定常性能的影响,以一台比转速为126的离心泵为研究对象,采用ANSYS CFX软件的标准k-ε湍流模型对同一叶轮、不同蜗壳进口宽度(56、63、66.5和70 mm)时,不同流量工况(0.8～1.2设计流量)条件下泵的外特性、内部流场以及压力脉动进行研究。结果表明:在设计流量下,适当改变蜗壳进口宽度对离心泵的扬程、效率影响不大;但随着蜗壳进口宽度的增大,蜗壳隔舌处的湍动能增大并向扩散段延伸;同时,蜗壳隔舌处压力脉动的压力值增大了4.2%,压力脉动幅值增大了3.4倍。设计时为提高中比转速离心泵的综合性能,应取蜗壳进口宽度为叶轮出口直径的1.8倍。     

离心压气机错排叶栅扩压器性能研究

依据叶片设计的基本理论,在原设计单列圆弧叶栅扩压器的基础上,根据相似准则设计了一种新型的双列错排叶栅扩压器;同时利用NACA叶型又设计了另一种双列错排叶栅扩压器。随后重点对三种扩压器与离心叶轮相连后的结构性能进行了详细的三维粘性数值模拟研究,并对流场中的压力、速度、极限流线和熵分布情况进行了全面的分析。研究结果表明：基于NACA叶型的双列错排叶栅扩压器可以更好地利用叶轮出口的动能,从而提高叶轮-扩压器结构的效率;但若叶栅的叶型设计不合理,则会使总压比降低,效率反而降低,即叶型对错排叶栅扩压器的性能影响较大。     

Experimental and numerical investigation on application of half vane diffusers for centrifugal pump

Vaned diffusers are widely used in centrifugal pumps, but little research has been published regarding action mechanism and the influence of diffuser vane height on dynamics performance of centrifugal pumps. Experimentally and numerically, the present investigation was focused on the dynamics performances of a low specific speed centrifugal pump equipped with vane diffusers with different vane heights. The pump performance was appraised when the diffuser vane height (h/b) was 0 (vaneless), 0.5, 0.6, 0.8 and 1 (vaned) times the diffuser width respectively. The pressure fields were numerically simulated in order to study the influence of half vane diffusers on inner flow field. The experimental results of operating performance showed that the efficiency was significantly improved for 2.5% at design flow point and the head was significantly improved for nearly 3 m at over flow point. The best efficiency point shifted towards higher flow rate with h/b reducing, and the high efficiency area was broadened by using half vane diffusers. Besides, half vane diffusers could reduce the intensity of pressure fluctuations at the leading edge of the stator vanes, and reduce the influence of rotor-stator interaction in tongue region. The numerical results showed that half vane diffusers could enhance flow uniformity in pumps, symmetry of pressure distributions on the impeller outlet and preferable regularity of radial force distributions. Therefore, it is very useful and feasible to apply half vane diffusers in centrifugal pumps.     

Numerical investigation on influence of diffuser vane height of centrifugal pump

Vaned diffusers are extensively used in centrifugal pumps, but the influence of vane height on internal flow field and overall performance is not explicit. This paper mainly presents numerical investigation on influence mechanism of diffuser vane height in a single-stage centrifugal pump. The head values were carried out on a low specific speed centrifugal pump equipped with different diffuser vane height by numerical simulation and experimental method. And the deviation between numerical results and experimental results were < 5%. The diffuser vane height h/b ratio is changed as 0, 0.3, 0.4, 0.5, 0.6, 0.8, and 1 in this study. The numerical analysis shows that reducing diffuser vane height could eliminate the vortex which appears at tongue region. Meanwhile, the influence of rotor-stator interaction was reduced by reducing the vane height. Consequently, the energy loss in the volute and the diffuser could both be decreased at design flow point and over flow point. In the other hand, the circumferential velocity at partial flow point gets larger which could lead to large frictional loss. In general, reducing the diffuser vane height at design and over flow point could improve the output work of impeller.     

多级离心泵叶轮相位交错对转子受力变化影响的研究

本文以一六级多级离心泵为模型,设计A、B、C、D四组不同的交错方案,A为叶轮相位不交错、 B为叶轮相位交错一个流道相位的1/2、C为叶轮相位交错一个流道的1/(Z-1)、D为叶轮相位交错一个导叶流道的1/(Z-1)(其中Z叶轮为叶片数)。通过四组方案对多级离心泵的三维全流场进行数值分析,得到不同叶轮交错方案在不同工况条件下流场对机械部件的荷载变化。分析结果表明：叶轮相位交错使转子的径向力矢量分布向轴心集中;叶轮相位交错结构可以有效地减小转子受到的径向力,使转子运行稳定性得到提高;叶轮相位交错会造成不同工况下的转子受力波动幅值和成分发生改变;在设计工况下数值计算轴向力绝对值要高于理论计算的结果     

超低比转速离心风机无叶扩压器改进设计研究

为了提高超低比转速离心通风机的气动性能,通过理论分析提出了降低超低比转速离心风机内部损失的扩压器设计方法,采用数值模拟的方法得到不同直径旋转扩压器和静止扩压器的性能特点,从风机静压、效率、扩压器静压恢复系数和滞止压力损失系数等方面对其分析比较。研究得到：在设计流量下,旋转扩压器直径增大8.7%后,风机静压提升6.8%,效率提高3%,扩压器静压恢复系数提高62.9%,扩压器内滞止压力损失减少71.9%,表明在尺寸允许范围内适当增大扩压器直径可获得更高的静压升,同时降低损失、提高效率;另外,静止扩压器壁面与通流之间的剪切力更大,损失更多,设计流量下静止扩压器比等直径旋转扩压器滞止压力损失增加75.2%,表明旋转扩压器比静止扩压器有更好的性能。     

The influence of wedge diffuser blade number and divergence angle on the performance of a high pressure ratio centrifugal compressor

Wedge diffuser is widely used in centrifugal compressors due to its high performance and compact size. This paper is aimed to research the influence of wedge diffuser blade number and divergence angle on centrifugal compressor performance. The impact of wedge diffuser blade number on compressor stage performance is investigated, and then the wedge diffusers with different divergence angle are studied by varying diffuser wedge angle and blade number simultaneously. It is found that wedge diffuser with 27 blades could have about 0.8% higher adiabatic efficiency and 0.14 higher total pressure ratio than the wedge diffuser with 19 blades and the best compressor performance is achieved when diffuser divergence angle is 8.3°.These results could give some advices on centrifugal compressor design.     

Pump-induced fluctuating pressure in a reactor coolant pipe

An analytical model is proposed to describe the propagation of pressure pulsations originated at the pump outlet through the inlet pipe of a pressurised water reactor (PWR). Pressure pulsations data from a pre-critical vibration monitoring programme (PVMP) for a C-E reactor are presented and compared with those calculated by the analytical model. The propagation of pump-induced pressure pulsation is important because of the potential for vibration and resultant damage of reactor internals.

The theory of pump-induced pressure pulsation distributions in the coolant annulus in a PWR has been developed by Penzes¹ and by Bowers and Horvoy² on the assumption that the pressure pulsations are due to excitations at the inlet nozzles. The pressures in the annulus are calculated based on prescribing the pressure at the inlet nozzles and on the concept of time dependent body force in the governing differential equations. The analytical model presented in the present paper and the theory given by Penzes¹ and Bowers and Horvoy² describe the propagation of pump-induced pressure pulsations in the critical regions (from the pump outlet through the inlet pipe and the coolant annulus in a PWR) for deterministic loads on PWR internals.

In the present analytical model the pressure pulsations are assumed to travel in plane waves so that the governing equation is one-dimensional in nature. The boundary condition at the pump outlet end of the inlet pipe is a time-dependent harmonic function; amplitudes for pump related frequencies are established based on an existing theory for hydraulic noise in centrifugal pumps.³ At the inlet nozzle end of the inlet pipe, due to the complexity of its acoustic characteristic, three types of boundary condition are considered—open, closed and piston-spring supported. Therefore, the analytical model essentially consists of a one-dimensional wave equation with time-dependent non-homogeneous boundary conditions. Closed-form solutions for the problem are derived using a linear transformation technique which reduces the problem to one involving a non-homogeneous differential equation with homogeneous boundary conditions.

Numerical examples are given for a typical reactor. Pressure power spectral density data are presented for data taken at inlet nozzles during a C-E PVMP. Distinct peaks at various pump related frequencies such as rotor speed, twice rotor speed, blade passing frequency and twice blade passing frequency, are observed. RMS pressures predicted by the analytical model at pump related frequencies are compared with those from PVMPs. The spatial distributions of the pressure field along the length of the inlet pipe for the three typical boundary conditions are given. Finally, the effect of the pipe geometry on the pressure field and the acoustic frequencies is analysed.     

The change of the inlet geometry of a centrifugal compressor stage and its influence on the compressor performance

The impact on the compressor performance is important for designing the inlet pipe of the centrifugal compressor of a vehicle turbocharger with different inlet pipes. First, an experiment was performed to determine the compressor performance from three cases: a straight inlet pipe, a long bent inlet pipe and a short bent inlet pipe. Next, dynamic sensors were installed in key positions to collect the sign of the unsteady pressure of the centrifugal compressor. Combined with the results of numerical simulations, the total pressure distortion in the pipes, the pressure distributions on the blades and the pressure variability in the diffuser are studied in detail. The results can be summarized as follows: a bent pipe results in an inlet distortion to the compressor, which leads to performance degradation, and the effect is more apparent as the mass flow rate increases. The distortion induced by the bent inlet is not only influenced by the distance between the outlet of the bent section and the leading edge of the impeller but also by the impeller rotation. The flow fields in the centrifugal impeller and the diffuser are influenced by a coupling effect produced by the upstream inlet distortion and the downstream blocking effect from the volute tongue. If the inlet geometry is changed, the distributions and the fluctuation intensities of the static pressure on the main blade surface of the centrifugal impeller and in the diffuser are changed accordingly.     

Experimental study of operation performance for hydrocarbon fuel pump with low specific speed

In this paper,a small flow rate hydrocarbon turbine pump was used to pressurize the fuel supply system of scramjet engine.Some experiments were carried out to investigate the characteristics of turbine pump driven by nitrogen or combustion gas under different operating conditions.A experimental database with regard to the curves of the rotational speed,mass flow rate and net head with regard to centrifugal pump were plotted.These curves were represented as functions of the pressure and temperature at turbine inlet/outlet and the throttle diameter at downstream of centrifugal pump.A sensitivity study has been carried out based on design of experiments.The experimental was employed to analyze net head of centrifugal and throttle characteristics.The research results can accumulate foundations for the close loop control system of turbine pump.