Statistical analysis of pressure fluctuations during unsteady flow for low-specific-speed centrifugal pumps

A three-dimensional transient numerical simulation was conducted to study the pressure fluctuations in low-specific-speed centrifugal pumps. The characteristics of the inner flow were investigated using the SST k-ω turbulence model. The distributions of pressure fluctuations in the impeller and the volute were recorded, and the pressure fluctuation intensity was analyzed comprehensively, at the design condition, using statistical methods. The results show that the pressure fluctuation intensity increases along the impeller streamline from the leading edge to the trailing edge. In the impeller passage, the intensity near the shroud is much higher than that near the hub at thc inlet. However, the intensity at the middle passage is almost equal to the intensity at the outlet. The pressure fluctuation intensity is the highest at the trailing edge on the pressure side and near the tongue because of the rotor-stator interaction. The distribution of pressure fluctuation intensity is symmetrical in the axial cross sections of the volute channel. However, this intensity decreases with increasing radial distance. Hence, the pressure fluctuation intensity can be reduced by modifying the geometry of the leading edge in the impeller and the tongue in the volute.

Optimization on the Impeller of a Low-specific-speed Centrifugal Pump for Hydraulic Performance Improvement

In order to widen the high-efficiency operating range of a low-specific-speed centrifugal pump, an optimization process for considering efficiencies under 1.0Qd and 1.4Qd is proposed. Three parameters, namely, the blade outlet width b2, blade outlet angle β2, and blade wrap angle φ, are selected as design variables. Impellers are generated using the optimal Latin hypercube sampling method. The pump efficiencies are calculated using the software CFX 14.5 at two operating points selected as objectives. Surrogate models are also constructed to analyze the relationship between the objectives and the design variables. Finally, the particle swarm optimization algorithm is applied to calculate the surrogate model to determine the best combination of the impeller parameters. The results show that the performance curve predicted by numerical simulation has a good agreement with the experimental results. Compared with the efficiencies of the original impeller, the hydraulic efficiencies of the optimized impeller are increased by 4.18% and 0.62% under 1.0Qd and 1.4Qd, respectively. The comparison of inner flow between the original pump and optimized one illustrates the improvement of performance. The optimization process can provide a useful reference on performance improvement of other pumps, even on reduction of pressure fluctuations.

Effect of impeller reflux balance holes on pressure and axial force of centrifugal pump

The size of impeller reflux holes for centrifugal pump has influence on the pressure distribution of front and rear shrouds and rear pump chamber, as well as energy characteristics of whole pump and axial force. Low specific-speed centrifugal pump with Q=12.5 m3/h, H=60 m, n=2950 r/min was selected to be designed with eight axial reflux balance holes with 4.5 mm in diameter. The simulated Q-H curve and net positive suction head(NPSH) were in good agreement with experimental results, which illustrated that centrifugal pump with axial reflux balance holes was superior in the cavitation characteristic; however, it showed to little superiority in head and efficiency. The pressure in rear pump chamber at 0.6 times rate flow is 29.36% of pressure difference between outlet and inlet, which reduces to 29.10% at rate flow and 28.33% at 1.4 times rate flow. As the whole, the pressure distribution on front and rear shrouds from simulation results is not a standard parabola, and axial force decreases as flow rate increases. Radical reflux balance holes chosen to be 5.2 mm and 5.9 mm in diameter were further designed with other hydraulic parts unchanged. With structural grids adopted for total flow field, contrast numerical simulation on internal flow characteristics was conducted based on momentum equations and standard turbulence model(κ-ε). It is found that axial force of pump with radical reflux balance holes of5.2 mm and 5.9 mm in diameter is significantly less than that with radical reflux balance holes of 4.5 mm in diameter. Better axial force balance is obtained as the ratio of area of reflux balance holes and area of sealing ring exceeds 6.

CAVITATING SUPPRESSION OF LOW SPECIFIC SPEED CENTRIFUGAL PUMP WITH GAP DRAINAGE BLADES

This paper aims to clarify the cavitation suppression mechanism of the gap structure impeller based on the analysis of cavitation characteristics in a low specific speed centrifugal pump. In order to obtain reliable and consistent numerical results, some numerical considerations and modeling methodology were demonstrated and researched, and a check of the time and space resolution were also conducted. Hence the predicted cavitation performance of the two centrifugal pumps were investigated and compared with experimental results, and they were in qualitative agreement. It was confirmed that the new gap structure impeller has a very good characteristic of inhibiting cavitation, especially in large flow area, the present numerical method can effectively capture the major internal flow features in the centrifugal pump, through the comparison of the two type impeller flow fields, the cavitation suppression mechanism of the gap impeller may be the combination effects of the small vice blade＇s guiding flow and gap tunnel＇s auto-balancing of pressure.

HYDRODYNAMIC OPTIMIZATION DESIGN OF LOW SOLIDITY VANED DIFFUSER FOR A CENTRIFUGAL PUMP USING GENETIC ALGORITHMS

This paper presents a hydrodynamic redesign of the conventional vaneddiffuser into the low solidity varied diffuser for the maximum static pressure recovery in acentrifugal pump. A Bezier curve representation for profile description was coupled with ablade-to-blade flow calculation and a real-coded genetic algorithm. A low solidity vaned diffuser of0.89 in solidity was obtained through the present optimum design. Numerical analysis andexperimental test were made to evaluate the hydrodynamic performance of the centrifugal pump withthe designed low solidity vaned diffuser and original vaned diffuser. The obtained resultsdemonstrate that the centrifugal pump with the optimized vaned diffuser has compact size comparedwith the original one while the performance requirements have been met.

叶顶间隙对低比转数小流量泵性能的影响

为建立叶顶间隙对低比转速小流量泵性能的影响关系,采用数值计算的方法,以叶顶间隙宽s和叶轮出口宽b的比值(s/b)表征间隙大小,对不同间隙下泵的性能展开对比分析。分析发现,随着间隙的增加,泵的扬程和效率均逐渐降低,最大和最小间隙下的扬程和效率差分别达15.4%,5.5%。当间隙较小即s/b<0.2时,扬程曲线在小流量工况会出现不稳定的“驼峰”现象,在s/b>0.3后,设计工况附近效率的降幅显著增大。从流动特性来看,随着叶顶间隙的增大,间隙泄漏流对叶轮内主流区影响加剧,会诱导严重的二次流和旋涡的产生,同时间隙内不稳定流动也会产生能量损失,造成扬程和效率下降。为低比转数小流量泵的设计与优化提供借鉴意义。

基于MOP的低比转速离心泵优化设计研究

针对传统低比转速离心泵效率偏低的问题,提出一种实现低比转速离心泵快速和智能化优化方法。以IS 80-50-250型低比转速离心泵为研究对象,采用叶轮机械设计软件CFturbo提取叶轮子午流道和叶片型线控制点参数;利用最佳预测元模型(MOP)和梯度算法得到优化后的参数和三维模型;对优化前、后的水力模型进行CFD数值计算,通过试验验证了数值计算的准确性,并分析优化前、后水力模型性能和流态,验证了优化方法的可行性。结果表明:在设计工况下,通过优化方法得到优化泵的效率与数值计算得到的效率高度一致,说明该方法可以实现离心泵的优化设计,优化后泵的效率提升了2.86%,扬程提高了2.08 m,优化效果较为显著,且优化后泵内部流动得到了较为明显的改善。研究结果对提高离心泵的水力性能具有借鉴意义。

离心泵叶轮动应力的长短期记忆网络预测与疲劳分析

低比转速离心泵在运行时会伴随着应力集中问题,应力集中和动应力变化可能导致低比转速离心泵发生疲劳损伤。传统的有限元方法在分析应力疲劳问题时受限于预测能力不足。本文提出了一种基于长短期记忆网络(LSTM)的离心泵疲劳寿命预测方法,通过利用长短期记忆网络对额定工况和小流量工况下动应力时间序列信号进行训练及预测,并结合疲劳寿命模型对不同运行条件下的离心泵运行寿命进行预测。结果表明:LSTM模型能够准确捕捉动应力的变化趋势,额定工况下的动应力拟合效果明显优于小流量工况。额定工况下动应力预测集MAPE值相较于小流量工况下降了21.33%。预测动应力为2.28×10^(7)Pa时,其运行寿命可达3×10^(8)的循环次数,满足高强度运行的寿命要求。本文所提出的方法能够有效提高离心泵的运行寿命预测精度,为离心泵的管理和维护提供更可靠的支持。

低温离心泵入口多余物定位及在线监测报警系统设计

低温离心泵是大型低温系统中的关键设备。为确保系统的自适应性和稳定性,需要实时监测离心泵的运行状态。特别是在工作环境恶劣、供应介质品质不稳定的情况下,及时判断故障位置并提前进行报警尤为重要。基于此,设计一套低温离心泵入口多余物定位及在线监测报警系统。该系统在低温离心泵的各部件前后加装压强测点,并引入设备参数实时监测算法,以实现故障的定位和报警,为低温系统的在线监测和报警提供初步解决方案。

高效低压钻井液系统研制与应用

为了满足科威特地区9000 m超深井钻机的作业需求,研发了高效低压钻井液系统。该系统比同级别系统安全性高、工艺流程复杂、环境更友好,可同时满足水基钻井液、油基钻井液作业工况。首次在9000 m超深井钻机配套的低压钻井液系统上应用节能型搅拌器、多功能螺旋输送机、双机械密封离心泵,使得低压钻井液系统更加节能、环保。该系统采用双通道工艺流程,双层钻井液罐设计罐面通道更为顺畅。厂内试验结果表明,该系统噪声低于82 dB,设备轴承温升不高于32℃,工艺流程正常,满足设计要求。随钻机开展了2 h的设备运转试验和2 h的联调试验,低压钻井液系统工作稳定正常。研究成果丰富了钻机产品的多样性,可广泛应用于科威特、阿联酋、沙特等中东地区超深井作业。

低温液体泵的简介与常见故障分析

简单介绍了低温泵中最常见的两种形式的液体泵——低温离心泵、低温柱塞泵的工作原理,并分别以某钢厂75000 m3/h空分中使用的液氧泵和液氩泵为例,列举了低温泵运行中的常见故障及维护手段。通过总结提炼,加快了设备故障排除及维护速度,提升了设备管理人员管理水平。

低比转数离心泵叶轮内能量转换特性

对比转数为60的离心泵内部流场进行数值模拟计算,从叶轮做功过程和能量损失过程两方面分析了叶轮内能量转换特性。将叶轮按径向尺寸分为8个区域,展示了不同工况、不同区域中压力和粘性力做功大小、功率密度分布、湍动能耗散率分布、能量损失组成及分布等能量转换相关特征。结果表明,叶轮进口区域能量转换效率相对较低且受叶片进口安放角影响,叶轮中部区域是叶轮做功和流体获得能量的关键区域,叶轮出口区域对叶轮性能有显著影响,壁面摩擦损失是叶轮内能量损失的主要组成部分。

长短叶片离心泵正交试验研究

试验设计选择了短叶片进口直径、进口偏置角和出口偏置角3个因素,每因素取3个水平,按L9(33)正交试验方案,设计制作了9副长短叶片复合叶轮,并对其外特性进行试验研究,检测出9副叶轮的动力特性.试验结果表明:短叶片设置对泵扬程有一定的提高,但效率差异较大,当取短叶片进口直径0.4(D2-D1)+D1,进口偏置角10,°出口偏置角0°时,泵的性能有明显改善.

低比转数离心泵内部非定常流动特性数值预测

为了深入研究低比转数离心泵在运行过程中内部的非定常不稳定流动现象的内在机理,采用CFD数值模拟的方法对模型泵内部三维湍流流场进行数值计算,并根据离心泵速度三角形推导了用来直观定量衡量流动非定常强度的时均非定常强度系数。通过分析该时均非定常强度系数在低比转数模型泵中的分布可知,叶轮叶片背面附近流场非定常性较强,且流体流经叶片后缘产生的尾迹现象同样随时间波动明显。蜗壳流道出口管及靠近叶轮出口处流动非定常性较强。

低比转速离心泵范围的界定

对国内外大量低比转速离心泵有关资料进行了统计研究和计算 ,分析了低比转速泵内各种水力损失和结构指标 ,提出了低比转速离心泵的比转速划分范围 。

离心泵小流量工况下的内部流动特性

为研究离心泵在小流量工况运行下性能及其内部流动特性,以型号为IS160-50-65的离心泵为研究对象,采用商用化软件Ansys CFX 12.0对模型离心泵的叶轮进口、叶轮流道以及蜗壳流道组成的全流场进行定常数值计算.同时,为了提高数值计算的准确性,考虑采用3种不同的网格数对模型离心泵的扬程进行网格无关性分析.且从离心泵的外特性及其内部流场分析了不同小流量工况下离心泵性能的变化规律.研究结果表明:与试验结果相比,设计工况下,扬程预测偏差为1.47%,效率预测偏差为3.61%;且随着流量降低,计算扬程的偏差值呈一定的下降趋势,计算效率的偏差值逐渐增大.另外,在设计工况下,离心泵的内部流动比较均匀;而在小流量工况下,离心泵进口管道及叶轮流道均出现回流现象,而回流引起的旋涡流有时甚至会堵塞叶轮流道;在极小流量Q/Qd=0.2时,回流区域已延伸至全部的进水管路中.

叶片数对离心泵小流量工况空化特性的影响

为研究小流量下离心泵的空化特性,采用ANSYS CFX 14.5,基于k-ε湍流模型和Rayleigh-Plesset空化模型,以3种叶片数叶轮的IS50-65-160型离心泵为研究对象,对其内部空化流动分别进行了数值模拟。为了提高数值计算准确性,进行了网格无关性分析,且从泵空化性能、叶轮所受扭矩及轴向力分析了叶片数对泵小流量下空化特性的影响规律。研究结果表明:当叶片数从4增加至8时,离心泵扬程增加,但其效率变化较复杂。小流量工况下,随着空化系数降低,各叶片数叶轮扭矩与泵扬程均不同步地发生陡降,且出现相似地匍匐下降规律;当扬程下降3%后,各叶轮所受轴向力的大小几乎恒定;单个叶片流道的空泡体积出现突增,明显较其他叶片流道大,各叶片流道空泡分布极不对称。研究发现,离心泵扬程及扭矩匍匐下降特性很可能与不对称叶片空化相关。

低比转数离心泵驼峰工况附近内部流动特性分析

为了揭示驼峰的产生机理,采用CFD数值预报对低比转数离心泵驼峰工况附近内部流动特性进行了深入分析,建立了扬程与内部流动特性之间的关系.在0.1~1.6倍设计流量下扬程的模拟值与试验值的相对误差在3.62%以内,且预报驼峰所在工况与实测结果基本一致.对驼峰附近工况0.2,0.3,0.4倍设计流量下的内部流动进行了分析,预报结果表明：泵进口管道存在大量回流,造成叶轮进口预旋,诱发驼峰;各叶轮流道内均存在不同程度大小的旋涡,在0.2和0.3倍工况甚至堵塞了整个流道;存在旋涡的叶轮流道出口相对速度值较大,而绝对速度值较小.结合泵基本方程进一步分析,发现出口相对流速的增大使得扬程降低,引发驼峰.对比叶轮出口R/R2=0.9处绝对速度,小流量下波动更加严重,且其圆周分量下降非常明显,直接降低了这些工况下的扬程值;叶轮进口的预旋及出口回流是诱发驼峰的原因,消除或者减小这些非稳态现象可作为抑制驼峰的出发点.

计算离心泵面积比和蜗壳面积的方法

依据离心泵的面积比原理,推导得出了计算离心泵面积比的计算公式,公式体现了面积比值和叶轮、蜗壳的水力参数关系。提出建立在面积比原理基础上、低比转速离心泵在加大流量设计后的面积比、蜗壳第八断面面积的计算方法及公式,面积比及蜗壳的第八断面面积和泵的流量加大系数、比转速加大系数得到了联系,也和叶轮、蜗壳的水力参数有关。解决泵行业一直依据经验统计值确定面积比而不能使低比转速离心泵在设计点效率最高这一问题。实例表明:提出的计算方法能够提高低比转速离心泵的效率,充实低比转速离心泵的设计理论。

低比转速复合叶轮离心泵内的非定常流动特性

为了研究低比转速离心泵内由叶轮/蜗壳相互作用所引起的非定常流动特性,基于滑移网格和RNGk-ε湍流模型计算了具有4长8短复合叶轮离心泵内部的非定常流动。计算结果显示,离心泵内部速度和压力在空间上呈现高度非对称性,在时间上呈现高度非定常性。蜗壳第Ⅳ断面和第Ⅷ断面速度变化规律基本一致,周向速度沿蜗壳径向减小,第Ⅷ断面出现负的径向速度,流动最为复杂。叶轮和蜗壳的动静耦合是产生压力脉动的主要原因,压力脉动的频率受叶轮转频控制,主频为叶片通过频率。蜗壳周向的脉动压力幅值呈现上下波动,但从第Ⅰ断面到第Ⅷ断面其幅值整体上在逐渐衰退,直到蜗壳第Ⅷ断面达到最小。与定常计算相比,在设计点下非定常计算所得的有效扬程更接近实验值,说明非定常计算可以比较准确地预测泵的扬程。