Numerical investigation on vibration and noise induced by unsteady flow in an axial-flow pump

Full-scale structural vibration and noise induced by flow in an axial-flow pump was simulated by a hybrid numerical method. An unsteady flow field was solved by a large eddy simulation-based computational fluid dynamics commercial code, Fluent. An experimental validation on pressure fluctuations was performed to impose an appropriate vibration exciting source. The consistency between the computed results and experimental tests were interesting. The modes of the axial-flow pump were computed by the finite element method. After that, the pump vibration and sound field were solved using a coupled vibro-acoustic model. The numerical results indicated that the the blade-passing frequency was the dominant frequency of the vibration acceleration of the pump. This result was consistent with frequency spectral characteristics of unsteady pressure fluctuation. Finally, comparisons of the vibration acceleration between the computed results and the experimental test were conducted. These comparisons validated the computed results. This study shows that using the hybrid numerical method to evaluate the flow-induced vibration and noise generated in an axial-flow pump is feasible.     

螺旋式纸浆离心泵内部流动的数值模拟

为分析螺旋式纸浆离心泵内部流动状态,给优化过流部件结构的优化设计提供基础,采用CFD分析软件Fluent对螺旋式离心泵内部单相流动和固液两相流动进行了数值模拟。给出了螺旋式叶轮建模方法和流场分析方法,分析了泵内流体速度和压力的分布特性,并基于流动模拟结果预测了水力性能,单相输送条件下的计算结果与试验结果取得了较好的一致。通过对一定体积浓度和颗粒粒径下固液两相流的研究计算,分析了螺旋式离心泵叶片表面以及流道内的固液相分布状态,对螺旋式结构的优化具有一定的参考意义。     

极大流量工况下离心泵内部流场数值分析

针对离心泵极大流量工况下内部流动特性的问题,应用流体动力学软件Fluent,采用RNGκ-ε湍流模型与SIMPLEC算法,对某一高比转速离心泵内部流场进行了数值模拟,并与实验结果进行了比较。对比分析了4种不同流量工况下离心泵内部流体速度和压力分布以及离心泵的外特性。研究结果表明,在设计流量工况下,离心泵内部压力分布均匀,速度迹线平滑;较大流量工况下,蜗壳压力不断减小,速度分布不均匀;极大流量(1.7Qopt)工况下,蜗壳出口处出现局部负压现象,速度流线产生的漩涡增大,在扩散管局部位置流体受到冲击,容易出现回流现象。针对离心泵在不同工况下以及达到极大流量工况下内部流动随流量变化规律的研究,可为高比转速离心泵多工况优化设计、延长使用寿命提供参考。     

Numerical study of a two-stage turbine characteristic under pulsating flow conditions

With developments of turbo-compounding and two-stage turbocharging technologies, two-stage turbine is increasingly applied in automotive engines. This paper numerically investigates the characteristic of a two-stage turbine on a turbo-compound engine under pulsating flow conditions. The behaviors of turbine stages with the swallowing capacity ratio (SR) equals to 2.0, under low, mid and high load conditions were studied. Results show that the Low pressure turbine (LPT) is more sensitive to the pulsating flow, especially at low load conditions, compared with High pressure turbine (HPT). It is caused by the dramatic change of velocity ratio in LPT. Results also show that the load split between HPT and LPT under pulsating flow conditions deviates from that at quasi-steady conditions, indicating the different behaviors of the two-stage turbine under pulsating conditions.     

离心泵内流场空化特性的数值模拟研究

针对离心泵内流场特性分析困难的问题,对离心泵流场数值模拟的几何模型建立、模型网格划分和边界条件设定进行了研究,采用计算流体力学方法,获取了在敞水性能条件下离心泵的扬程-流量、效率-流量的变化关系;结合Zwart空化模型,重点对不同有效汽蚀余量时离心泵的空化流场进行了数值模拟,得到了离心泵的内部流线和空泡分布的情况,并与该离心泵机组进行了性能测试实验,最后在此基础之上进行了对比分析。研究结果表明,所采用的数值模拟方法和空化模型合理有效,此结果可为进一步开展离心泵空化监测技术研究提供借鉴。     

Effects of clearance flow on the characteristics of centrifugal pump under low flow rate

Journal of Mechanical Science and Technology - The Reynolds averaged Navier-Stokes equations and the shear stress transport k-w turbulence model are employed to simulate the centrifugal pump with...     

电动燃油泵流道数值仿真及结构改进研究

针对电动燃油泵流道内液体流动规律复杂,工作效率需要改善的问题,运用Fluent软件对燃油泵内部流场进行仿真分析。基于雷诺时均N-S方程和标准K-∑湍流模型以及标准壁面函数法,采用三维非结构四面体网格划分方法,对包括不同叶片数、不同叶片夹角和不同叶轮厚度的燃油泵结构模型进行了数值模拟,得到了燃油泵内部流场压力云图和流线图。以燃油泵叶轮结构参数为变量,出口流量为目标函数,通过对仿真结果进行了数值拟合,得到了叶轮叶片数,叶片夹角,叶轮厚度和出口流量的一般规律。并通过燃油泵台架实验,对优选的燃油泵性能进行了验证。研究结果表明,实验数据与仿真结果基本吻合,且改进后的燃油泵流量提高了2.5%左右,其工作性能得到改善。     

基于数值建模的直线共轭内啮合齿轮泵流量特性分析

文中根据齿轮啮合基本原理,推导直线共轭内啮合齿轮副的齿廓方程,基于数值建模的方法建立三维模型进行运动仿真验证其正确性.在此基础上,用矢量射线法推导齿轮泵容腔容积角导数公式、流量公式,应用MATLAB编程分析齿轮泵齿数差、齿形半角对容腔容积角导数变化剧烈程度和流量脉动的影响,对直线共轭内啮合齿轮泵的理论设计和应用有重要指...     

Test investigation on hydraulic losses in the discharge passage of an axial-flow pump

In a discharge passage with a guide blade discharge circulation and secondary flow because of bend pipe, the flow in a 1-channel discharge passage of an axial flow pump is a complicated spiral flow. For a 2-channel passage, the discharge in the left channel is bigger than that in the right, and the passage hydraulic losses are abnormal. In this study, the section current energy of the passage is accurately measured and determined with a 5-hole probe. The hydraulic loss characteristics are determined and analyzed. The methods deducing the hydraulic losses are investigated. The results indicate that the passage hydraulic losses are not proportional to the flow discharge. Compared with a circular pipe, the hydraulic losses of a divergent discharge passage are smaller and the pump assembly efficiency is 10%–30% higher. As for the 1-channel passage, the axial-flow pump outlet circulation is usually too big; the passage hydraulic losses are also big, but a small circulation can slightly reduce hydraulic losses. As for the 2-channel passage, discharges in the two channels are not equal and the hydraulic losses increase. The outlet guide blade with a small discharge circulation or without circulation could reduce discharge passage hydraulic losses and increase pump assembly efficiency by 6%–11%. __________ Translated from Chinese Journal of Mechanical Engineering, 2006, 42(5): 39–44 [译自: 机械工程学报]     

Numerical investigation on the transient characteristics of sediment-laden two-phase flow in a centrifugal pump

The objective of this work was to determine pressure fluctuation and transient flow characteristics, which aims to provide references to improve noise and vibration performance for the pump design and optimization when delivering sediment-laden flow. The three-dimensional (3D) transient simulations were simulated by SST k-ω turbulence model combined with Homogeneous equilibrium model (HEM). The experimental and numerical data was compared to validate the numerical accuracy. The simulation results predicted that the concentration shows strong effects on the external performance, velocity, pressure, turbulent kinetic energy distribution and peak amplitude of pulsation frequency, which all perform increasing trend with the rise of concentration. Meanwhile, the effect of the diameter size of particles on the flow field was relatively minor, which can also evidently influence the internal flow, but the effect is not simply proportional to the diameter size. The effect of diameter size on silt flow needs to be taken into account associated with the concentration distribution. The dominant frequency of solid-liquid approximately equals 0.8 times that of pure water, and the transient characteristics of sediment-laden flow perform low frequency with high amplitude features.     

小流量工况下低比转速离心泵内部流场的数值分析

针对小流量工况下低比转速离心泵内部流动特性问题,通过运用计算流体力学软件FLUENT,并采用RNG k-ε湍流模型和SIMPLE算法,对离心泵内部流场进行了数值模拟。采用3种不同网格数对离心泵模型进行了网格无关性分析以验证提高数值计算的准确性。沿进水管道至其进口端设置了监测点,分析了周向速度和轴向速度,得出了不同工况下发生回流的位置,分析比较了4种流量工况下离心泵内部的流场分布。结果表明:0.7Qd工况下,进水管道和叶轮流道中的流线均比较平滑,离心泵内部流动比较稳定。0.6Qd工况下,叶轮进口和叶轮流道开始产生了漩涡。随着流量的进一步降低,叶轮进口回流强度增大,叶轮流道中的漩涡逐渐向其相邻流道中扩展,离心泵内部的流态十分紊乱。     

Numerical simulations of the internal flow pattern of a vortex pump compared to the Hamel-Oseen vortex

We did a numerical study of the internal flow field of a vortex pump. Five operating points were considered and validated through a measured characteristic curve. The internal flow pattern of a vortex pump was analyzed and compared to the Hamel-Oseen vortex model. The calculated flow field was assessed with respect to the circumferential velocity, the vorticity and the axial velocity. Whereas the trajectories of the circumferential velocity were largely in line with the Hamel-Oseen vortex model, the opposite was true for vorticity. Only the vorticity at strong part load was in line with the predictions of the Hamel-Oseen vortex model. We therefore compared the circumferential velocity and vorticity for strong part load operation to the analytical predictions of the Hamel-Oseen vortex model. The simulated values were below the analytical values. The study therefore suggests that a vortex similar to the Hamel-Oseen vortex is only present at the strong part load operation.     

Numerical study on the pulsatile flow characteristics of proximal anastomotic models

Haemodynamics was widely believed to correlate with anastomosis restenosis. Utilizing the haemodynamic parameters as indicator functions, distal anastomosis was redesigned by some researchers so as to improve the long-term graft patency rate. However, there were few studies upon the proximal anastomosis. Therefore, in this study, flow characteristics and distributions of the haemodynamic parameters in proximal anastomosis under physiological flow condition have been investigated numerically for three different grafting angles: namely, 45 degrees forward facing, 45 degrees backward facing, and 90 degrees anastomotic joints. The simulation results showed a flow separation region along the graft inner wall immediately after the heel at peak flow phase and it decreased in size with the grafting angle shifting from 45 degrees forward facing to 45 degrees backward facing. At the same time, a pair of vortex was found in the cross-sectional planes of the 45 degrees backward facing and 90 degrees grafts. In addition, stagnation point was found along the graft outer wall with small shifting during the physiological cycle. High spatial and temporal wall shear stresses gradients (WSSG) were observed around the anastomotic joint. Low time-averaged wall shear stress (WSS) with elevated oscillation shear index (OSI) was found near the middle of anastomosis at the aorta wall and along the graft inner wall respectively, while high time-averaged WSS with low OSI was found at the heel, the toe, and the region downstream of the toe. These regions correlated to early lesion growth. Elevated time-averaged WSSG was found at the same region, where the elevated low-density lipoprotein (LDL) permeability was observed as reported in the literature. The existence of nearly fixed stagnating location, flow separation, vortex, high time-averaged WSS with low OSI, low time-averaged WSS with elevated OSI, and high time-averaged WSSG may lead to graft stenosis. Moreover, the simulation results obtained were consistent with those of experimental measurements. Based on the validated simulation results, the 45 degrees backward-facing graft was found to have the lowest variation range of time-averaged WSS and the lowest segmental average of WSSG among the three models investigated. The 45 degrees backward-facing graft is thus recommended for the bypass operation with expected higher patency rate.     

水平轴风机失速状态下的数值分析

以变桨水平轴风机叶轮为研究对象,针对最大阵风停机顺桨状态下,利用FLUENT计算流体软件对风机的三维流场进行数值模拟分析,再对模拟的流场结果进行保存输出到有限元软件AN-SYS中作为结构计算的初始条件,进而进行结构计算。通过对风机叶轮进行流固分析,为风机的设计提供有利的参考,对风机叶轮的设计研究提供数值模拟依据。这种方法也可以应用到分析该风机在运动时候的状态,根据数值模拟结果进行优化设计能够改进风机的使用效率,这对节约能源、提高发电机的经济效益具有重要意义。     

The lubrication characteristics of the vane tip under inlet pressure boundary conditions for an oil hydraulic vane pump

The lubrication modes of line contact between the vane and the camring in an oil hydraulic vane pump have been investigated. First, variations of the radial acting force of a vane were calculated from previously measured results of the dynamic internal pressure in four chambers surrounding a vane. Next, distinctions of the lubrication modes were made using Hooke’s chart, which represents an improvement over Johnson’s chart. Finally, the influence of boundary conditions in the lubrication region on fluid film lubrication was examined by calculating film pressure distributions. The results show that the lubrication modes of the vane tip are a rigidvariable viscosity region. This region discharges pressure higher than 7 MPa, and exerts a great influence on oil film pressure in the large arc section due to the Piezo-viscous effect.     

Numerical simulation of water flow in an axial flow pump with adjustable guide vanes

A new adjustable guide vane (AGV) is proposed in this paper. This vane can reduce hydraulic losses and improve the performance of an axial flow pump. The formula of AGV adjustment was obtained after theoretical analysis. The fluid flow inside the axial flow pump with a fixed guide vane and adjustable guide vane was simulated. The calculated Q-H curves for the fixed guide vane agreed well with the experimental ones. The results show that the attack angle and flow separation have an important contribution to the vortices which create hydraulic losses in the guide vane channel. The AGV can decrease hydraulic losses and significantly enhance the pump head and efficiency by changing the guide vane angle.     

Numerical investigation of two-phase flow characteristics in multiphase pump with split vane impellers

Multiphase pump is a cost-effective option for subsea oil and gas field development. The ability to handle different inlet gas volume fractions (GVFs) especially high inlet GVF is critical to the development of pump performance. In this study, the two-phase flow characteristics in normal impeller and split vane impeller at different inlet GVFs were investigated by steady numerical simulations. The gas distribution on blade-to-blade plane and meridional flow channel at different inlet GVFs were analyzed and compared. Gas accumulation area and movement characteristics of the gas-liquid flow in impeller flow passage were also pointed out by unsteady simulations. Experimental results of the pump differential pressure were compared with the numerical simulation results, to validate the accuracy of numerical simulation method. The flow characteristics in pump with modified impeller and its performance at different inlet GVFs were both compared with that of the normal impeller. The steady simulation results of normal impeller in different inlet GVFs show that gas concentrating area in the flow passage increases as inlet GVF grows. The unsteady simulation results indicate that gas pocket firstly occurs on the pressure side of impeller, then moves to the suction side in the middle area of blade and finally transfers to outlet of impeller and disappears. The errors between numerical simulation results and experiment data are below 10 %, which validated the feasibility of the numerical simulation method. Simulation results on the split vane impeller demonstrate that the gas accumulation area in flow passage of the modified impeller is dramatically decreased compared to that of the normal impeller. The performance of the modified impeller is generally better than the normal impeller especially in high inlet GVF conditions.

     

Numerical simulation and analysis of flow characteristics in the front chamber of a centrifugal pump

We performed numerical simulations to study the flow characteristic in a centrifugal pump based on the RANS equations and the RNG k-ε turbulent model. The flow field, including the front and back pump chambers, the impeller wear-ring, the impeller passage, the volute casing, the inlet section and outlet section was calculated to obtain accurate numerical results of fluid flow in a centrifugal pump. The flow characteristic was studied from the internal flow structure in pump chambers, the radial velocity at impeller outlet as well as the pressure inside of the pump, the circumferential velocity and the radial velocity in front pump chamber. The variation of flow parameters in internal flow versus flow rate in the centrifugal pump was analyzed. The results show that the overall performance of the pump is in good agreement with the experimental data. The simulation results show that the distribution of flow field in the front pump chamber is axial asymmetry. The energy dissipation at the impeller outlet is larger than other areas. The distribution of the circumferential velocity and that of radial velocity are similar along the axial direction in the front pump chamber, but the distribution of flow is different along the circumferential and the radial directions. It was also found that the vorticity is large at the impeller inlet compared with other areas.     

多级离心泵首级叶轮停机特性数值研究

针对多级离心泵在突然断电情况下可能出现的意外事故问题,基于滑移网格技术、用户自定义函数和SIMPLE算法,在关死点处和给定转速下降规律情况下,对一多级离心泵首级叶轮的停机过程进行了内部非定常粘性流动的数值模拟,通过数值计算获得了多级离心泵首级叶轮停机过程的外特性和内部流场演化特性,重点分析了叶轮进口、叶轮出口和反导叶出口3个位置处的瞬态物理量变化。研究结果表明,无量纲扬程系数在停机之前和停机过程前期阶段基本不变,而在停机过程末期迅速下降,叶轮停止转动时,各个物理参数并未同步趋零,总之表现出明显的瞬态行为特征;叶轮出口处的物理量参数变化受叶轮转动影响最大,其次受叶轮进口处的参数变化影响,而反导叶出口处的参数变化最小。     

Study on unsteady tip leakage vortex cavitation in an axial-flow pump using an improved filter-based model

The aim of the present investigation is to simulate and analyze the tip leakage flow structure and instantaneous evolution of tip vortex cavitation in a scaled axial-flow pump model. The improved filter-based turbulence model based on the density correction and a homogeneous cavitation model were used for implementing this work. The results show that when entering into the tip clearance, the backward flow separates from the blade tip near the pressure side, resulting in the generation of a corner vortex with high magnitude of turbulence kinetic energy. Then, at the exit of the tip clearance, the leakage jets would re-attach on the blade tip wall. Moreover, the maximum swirling strength method was employed in identifying the TLV core and a counter-rotating induced vortex near the end-wall successfully. The three-dimensional cavitation patterns and in-plain cavitation structures obtained by the improved numerical method agree well with the experimental results. At the sheet cavitation trailing edge in the tip region, the perpendicular cavitation cloud induced by TLV sheds and migrates toward the pressure side of the neighboring blade. During its migration, it breaks down abruptly and generates a large number of small-scale cavities, leading to severe degradation of the pump performance, which is similar with the phenomenon observed by Tan et al. [35].