叶片与隔舌干涉对离心泵性能和压力脉动影响的数值研究

采用SST k-ω湍流模型对离心泵内部流场进行了三维非定常数值模拟,分析了不同时刻叶片与隔舌相对位置对模型泵瞬时性能及压力脉动的影响。利用数理统计学原理和时-频域数据处理方法对流场内监测点的压力脉动进行分析。结果显示:叶片与隔舌间的动静干涉引起模型泵瞬时性能呈周期性变化,瞬时扬程与瞬时效率波动较大而瞬时轴功率波动值较小;改进特定时刻叶片与隔舌相对位置处泵的最低瞬时性能是提高其总体性能的一条途径;隔舌及叶片附近均是较强的脉动源,脉动最强的部位不在隔舌顶部而是向螺旋线方向偏移;叶片通过频率是压力脉动的主要频率。     

交错叶片对双吸离心泵性能特性影响分析

为了积极响应及实现国产化要求,对原进口泵进行整机国产化研制,通过数值模拟分析了叶轮叶片交错角度为0°、15°、30°时离心泵内的流态和压力脉动。结果表明:随着叶片交错角度的增大,小流量工况下,扬程值逐渐降低,效率值无明显变化;大流量工况下,扬程值和效率值逐渐增大;额定工况下,随着叶片交错角度的增大,压出室对称分布的两个单独流道同一位置处静压值逐渐增大,相对速度值逐渐减小,而叶片处的相对速度值无明显变化。压出室内压力脉动幅值随着叶片交错角度的增大出现明显的减弱现象。同一叶片交错角度下,随着压出室过流断面的增加,压力脉动幅值逐渐减小,隔舌位置处压力脉动幅值受动静干涉作用最大。站场运行结果表明,叶片交错角度为30°的国产泵较原进口泵振动值减小、耗能降低、泵运行平稳且效率高。     

基于CFD的双流道泵内流特性分析

针对双流道泵小流量工况效率低、运行稳定性差等问题,通过CFD数值分析,对0.6Q_d、0.8Q_d、1.0Q_d、1.2Q_d工况下叶轮流动特性进行了压力、速度分布和隔舌处的压力脉动分析研究。结果表明:叶轮内压力分布存在明显的对称性,泵内各压力梯度所占区域随流量增加而增加,压力分布逐渐向高压区移动。叶轮截面1的速度随着流量增加而逐渐增大。在叶轮截面2内,叶轮内速度随着流量的增加而增加。叶轮进口旋涡随着流量增加而逐渐减小。流体经过截面2旋涡后,在截面3两侧流道内分别形成两个单独流动旋涡。在叶轮截面3内,叶轮流道内速度随着流量增加逐渐上升。隔舌处压力脉动具有周期性。设计工况下相邻波峰与波谷相差31.3 kPa。     

高速离心泵的压力脉动特性分析

为揭示高速离心泵的水力不稳定性,采用雷诺时均方法和SST k-ω湍流模型,对一带前置诱导轮和半开式复合叶轮的高速泵进行了不同工况下三维非定常湍流数值模拟,得到了泵内部流场特性及泵内监测点的压力脉动情况,并对其进行了频谱分析。结果表明,由于诱导轮、叶轮与扩压器的动静耦合作用,高速泵内存在比较明显的压力脉动。叶轮域从叶片入口到出口,压力脉动的峰峰值逐渐增加;相同径向位置处工作面的压力脉动明显高于非工作面。叶轮内压力脉动的频率为3fr(导叶叶片数×叶片通过频率)及其倍频,主频为3fr。导叶扩压器域内隔舌位置处的压力脉动峰峰值最大。随着水流向下游流动,扩压器内的压力脉动逐渐减小。螺旋线部分压力脉动的主频为3fr,与诱导轮叶片的通过频率相吻合。扩散段部分压力脉动的主频为7fr,与叶轮长叶片的通过频率吻合。     

旋流泵内部非定常压力脉动分析

为了深入分析旋流内部流场的压力脉动特性,建立旋流泵数值计算模型,基于标准k-ε湍流模型,开展旋流泵内部流动结构的非定常计算,分析旋流泵进口、出口及压水室的监测点的压力脉动情况,探讨各处压力时域与频域图变化规律,并对脉动特性进行试验验证。结果表明:不同工况下旋流泵压力波动呈现明显的周期性变化;叶轮与隔舌处的干涉作用是压力脉动的来源,隔舌处的脉动主频以叶频为主;旋流泵内部充满大量回流与漩涡,也是造成流动不稳定的因素,该研究结果为旋流泵的稳定运行提供了理论依据。     

长短叶片叶轮双吸离心泵径向力数值仿真

将1200S56型单级双吸离心泵原型叶轮改型为长短叶片复合叶轮,以该改型双吸长短叶片复合叶轮离心泵为研究对象,基于CFD理论对该离心泵内部流场进行数值仿真。通过改变边界条件获得不同工况下叶轮出口与蜗壳耦合面的静压、速度分布。采用叶轮出口压力法分析该离心泵在不同工况下的径向力,并与原型叶轮离心泵径向力分析结果对比。结果表明:采用长短叶片复合叶轮使叶轮出口的静压力及绝对速度变大,增加了离心泵的扬程,有效的提高了泵的整体水力性能;短叶片的增加使该泵径向力的最小值点向大流量偏移,出现在1.2倍额定流量工况,最小值由原型叶轮的5574N减小到1494N;采用长短叶片复合叶轮改善了泵在大流量工况下的径向受力情况。     

汽车冷却水泵小流量工况下非定常空化特性研究

针对汽车冷却水泵的空化问题,对小流量工况下非定常空化特性及其对压力脉动的影响进行了研究。采用SST k-ω湍流模型和Zwart-Gerber-Belamri (ZGB)空化模型,对水泵在典型空化状态下的流场进行了数值模拟研究,得到了小流量工况下叶轮内的非定常空化流动特征和空泡的时空演变规律;对蜗壳上的压力脉动进行了频谱分析,得到了不同空化条件对压力脉动的影响;通过泵的空化实验,对数值模拟结果进行了验证。研究结果表明:随着空化余量的减小,各监测点压力脉动峰的峰值和主频幅值逐渐增大,特别是隔舌位置处的压力脉动变化最为显著;泵内的空泡表现为不对称分布,主要集中在叶片前缘位置以及后盖板靠近叶轮进口位置,并随着空化的加剧,空泡体积分数逐渐增大。     

某混流泵压力脉动分析研究

为了研究某混流泵内部流场压力脉动情况,应用商业软件Numeca进行非定常数值模拟。通过设置监测点,得到了叶轮和导叶位置的压力脉动结果,并进行了频域分析。结果表明,泵内压力脉动变化规律是周期性的。在叶轮内,叶片尾缘的压力脉动幅值均大于前缘,而导叶内压力脉动幅度由叶片前缘到尾缘逐渐减小,与叶轮内压力脉动变化规律相反。     

侧壁式压水室离心泵的压力脉动特性

压力脉动是引起泵振动的主要因素之一,为有效地降低离心泵内压力脉动水平,提出具有特殊结构的侧壁式压水室。为研究其压力脉动特性,采用FLUENT软件对比转数130的侧壁式压水室离心泵进行数值计算,并将时域信号进行快速傅里叶变换为频域信号,结果如下:由于叶轮和隔舌的动静干涉作用,侧壁式压水室内压力脉动周期性明显,叶频在由压力脉动诱发的振动中占主导作用;由于隔舌位置及结构的变化,叶轮出口处液流与隔舌的直接冲击、干涉作用减弱,因此侧壁式压水室内隔舌附近监测点处的脉动幅值并未明显地高于其他点。与常规螺旋形压水室相比,侧壁式压水室可以大幅地降低泵内压力脉动水平,因此采用侧壁式压水室可以显著地降低由压力脉动诱发的振动,改善泵的振动性能。     

偏离工况下离心泵的压力脉动和振动分析

为分析偏离工况下离心泵压力脉动和振动情况,本文采用大涡模拟和滑移网格技术研究一离心泵在偏离工况下叶轮内部和叶轮与蜗壳动静干涉位置的压力脉动,并对其进行了频域分析。分析结果表明:离心泵内部流动产生的压力脉动主频多数情况下是其通过频率。在不同运行工况下,叶轮出口处的压力脉动幅值均最大,大流量偏离工况下离心泵内部各部分压力脉动特性与设计工况基本相同,只是脉动幅值略有增大;小流量偏离工况下,离心泵叶轮出口(叶轮和蜗壳动静干涉区域)压力脉动幅值有所增大,脉动主频不再是通过频率,而且其频谱宽度明显增大;当离心泵运行工况小于0.6Q时,压力脉动明显比设计工况剧烈。     

Influence of blade thickness on transient flow characteristics of centrifugal slurry pump with semi-open impeller

As the critical component, the impellers of the slurry pumps usually have blades of a large thickness. The increasing excretion coefficient of the blades affects the flow in the impeller resulting in a relatively higher hydraulic loss, which is rarely reported. In order to investigate the influence of blade thickness on the transient flow characteristics of a centrifugal slurry pump with a semi-open impeller, transient numerical simulations were carried out on six impellers, of which the meridional blade thickness from the leading edge to trailing edge varied from 5-10 mm, 5-15 mm, 5-20 mm, 10-10 mm, 10-15 mm, and 10-20 mm, respectively. Then, two of the six impellers, namely cases 4 and 6, were manufactured and experimentally tested for hydraulic performance to verify the simulation results. Results of these tests agreed reasonably well with those of the numerical simulation. The results demonstrate that when blade thickness increases, pressure fluctuations at the outlet of the impeller become severe. Moreover, the standard deviation of the relative velocity in the middle portion of the suction sides of the blades decreases and that at the outlet of the impeller increases. Thus, the amplitude of the impeller head pulsation for each case increases. Meanwhile, the distribution of the time-averaged relative flow angle becomes less uniform and decreases at the outlet of the impeller. Hence, as the impeller blade thickness increases, the pump head drops rapidly and the maximum efficiency point is offset to a lower flow rate condition. As the thickness of blade trailing edge increases by 10 mm, the head of the pump drops by approximately 5 m, which is approximately 10 % of the original pump head. Futhermore, it is for the first time that the time-averaged relative flow angle is being considered for the analysis of transient flow in centrifugal pump. The presented work could be a useful guideline in engineering practice when designing a centrifugal slurry pump with thick impeller blades.

     

不同形式高速离心叶轮内部流动的数值模拟

为分析叶轮结构对于叶轮内部流动的影响,对8叶片的闭式和半开式两种形式低比转速高速离心复合叶轮进行研究.采用S-A湍流模型和雷诺时均N-S方程,对叶轮内部的流动进行三维紊流数值计算和分析,并对离心泵进行试验研究.数值计算结果表明,两种形式叶轮内部都存在回流,其中半开式叶轮内部的回流区域较少,液流在间隙里的相对流动大致为圆周方向;叶轮内部的静压力都是由叶片进口到出口逐渐升高,等静压曲线几乎是沿圆周方向,半开式叶轮叶片顶部的静压力低于相应位置根部的静压力,闭式叶轮出口的压力系数高于半开式叶轮.试验结果表明,半开式叶轮离心泵的效率较高,说明叶轮内部的回流是影响离心泵性能的重要因素.     

不同叶片数下管道泵内部流动及振动特性的数值与试验研究

为研究不同叶片数下管道泵内部的流动特性及振动特性,采用标准k-ε湍流模型和滑移网格技术,在CFX数值计算软件中,分别对6叶片和7叶片的管道泵内部全流场进行三维非定常数值模拟,计算得到不同流量下叶轮内部流动特性、蜗壳内部静压特性以及叶轮转矩波动特性。对比0.1qV工况下两种叶片数下的数值计算结果,发现6叶片下的“射流-尾迹”效应及静压变化梯度均大于7叶片,6叶片下的转矩波动强度大于7叶片;不同叶片数下,叶轮内部的相对速度变化规律、静压变化规律以及蜗舌附近低压区的发展变化规律与蜗舌和叶轮的相对位置有关。采用振动试验测量不同叶片数下管道泵的振动水平,分析振动试验结果和数值计算结果表明,在不同流量下,6叶片的振动水平高于7叶片,主要在于6叶片具有较强的压力脉动和不稳定流体力的作用;叶频及其倍频是管道泵产生振动的主要激励频率。因此,可以通过优化叶片设计参数(Z,β2,β1)来改善管道泵内部的不稳定流动状态,进而降低振动水平。     

超低比转速复合式离心泵内部流动特性分析

为研究超低比转速复合式离心泵内部流动特性,以一台比转速为16、半开式复合叶轮离心泵为研究对象,应用ANSYS-Fluent19R1软件对模型泵进行三维全流场数值模拟计算,得出泵内部流场及作用在叶轮、蜗壳上的径向力分布规律。结果表明:在不同流量工况下,随着流量的增加,在隔舌附近出现较大的压力梯度;在长叶片与短叶片相间隔流道内低速区面积较大、叶轮出口处分布较多的旋涡;当流量从0.2倍增加至1.8倍额定流量时,作用在蜗壳上的径向力幅值逐渐减小,作用在叶轮上的径向力幅值先减小后增加,在1.0倍额定流量时径向力幅值达到最小,而后增大。为超低比转速复合式离心泵的设计优化提供参考。     

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。     

Investigation on Reduction of Pressure Fluctuation for a Double-Suction Centrifugal Pump

Double-suction centrifugal pumps have been applied extensively in many areas,and the significance of pressure fluctuations inside these pumps with large power is becoming increasingly important.In this study,a double-suction centrifugal pump with a high-demand for vibration and noise was redesigned by increasing the flow uniformity at the impeller discharge,implemented by combinations of more than two parameters.First,increasing the number of the impeller blades was intended to enhance the bounding effect that the blades imposed on the fluid.Subsequently,increasing the radial gap between the impeller and volute was applied to reduce the rotor-stator interaction.Finally,the staggered arrangement was optimized to weaken the efficacy of the interference superposition.Based on numerical simulation,the steady and unsteady characteristics of the pump models were calculated.From the fluctuation analysis in the frequency domain,the dimensionless pressure fluctuation amplitude at the blade passing frequency and its harmonics,located on the monitoring points in the redesigned pumps(both with larger radial gap)are reduced a lot.Further,in the volute of the model with new impellers staggered at 12°,the average value for the dimensionless pressure fluctuation amplitude decreases to 6% of that in prototype pump.The dimensionless rootmean-square pressure contour on the mid-span of the impeller tends to be more uniform in the redesigned models(both with larger radial gap);similarly,the pressure contour on the mid-section of the volute presents good uniformity in these models,which in turn demonstrating a reduction in the pressure fluctuation intensity.The results reveal the mechanism of pressure fluctuation reduction in a double-suction centrifugal pump,and the results of this study could provide a reference for pressure fluctuation reduction and vibration performance reinforcement of doublesuction centrifugal pumps and other pumps.     

Influence of blade wrap angle on centrifugal pump performance by numerical and experimental study

The existing research on improving the hydraulic performance of centrifugal pumps mainly focuses on the design method and the parameter optimization. The traditional design method for centrifugal impellers relies more on experience of engineers that typically only satisfies the continuity equation of the fluid. In this study, on the basis of the direct and inverse iteration design method which simultaneously solves the continuity and motion equations of the fluid and shapes the blade geometry by controlling the wrap angle, three centrifugal pump impellers are designed by altering blade wrap angles while keeping other parameters constant. The three-dimensional flow fields in three centrifugal pumps are numerically simulated, and the simulation results illustrate that the blade with larger wrap angle has more powerful control ability on the flow pattern in impeller. The three pumps have nearly the same pressure distributions at the small flow rate, but the pressure gradient increase in the pump with the largest wrap angle is smoother than the other two pumps at the design and large flow rates. The pump head and efficiency are also influenced by the blade wrap angle. The highest head and efficiency are also observed for the largest angle. An experiment rig is designed and built to test the performance of the pump with the largest wrap angle. The test results show that the wide space of its efficiency area and the stability of its operation ensure the excellent performance of the design method and verify the numerical analysis. The analysis on influence of the blade wrap angle for centrifugal pump performance in this paper can be beneficial to the optimization design of the centrifugal pump.     

Effects of Blade Number on Characteristics of Centrifugal Pumps

The blade number of impeller is an important design parameter of pumps,which affects the characteristics of pump heavily.At present,the investigation focuses mostly on the performance characteristics of axis flow pumps,the influence of blade number on inner flow filed and characteristics of centrifugal pump has not been understood completely.Therefore,the methods of numerical simulation and experimental verification are used to investigate the effects of blade number on flow field and characteristics of a centrifugal pump.The model pump has a design specific speed of 92.7 and an impeller with 5 blades.The blade number is varied to 4,6,7 with the casing and other geometric parameters keep constant.The inner flow fields and characteristics of the centrifugal pumps with different blade number are simulated and predicted in non-cavitation and cavitation conditions by using commercial code FLUENT.The impellers with different blade number are made by using rapid prototyping,and their characteristics are tested in an open loop.The comparison between prediction values and experimental results indicates that the prediction results are satisfied.The maximum discrepancy of prediction results for head,efficiency and required net positive suction head are 4.83%,3.9% and 0.36 m,respectively.The flow analysis displays that blade number change has an important effect on the area of low pressure region behind the blade inlet and jet-wake structure in impellers.With the increase of blade number,the head of the model pumps increases too,the variable regulation of efficiency and cavitation characteristics are complicated,but there are optimum values of blade number for each one.The research results are helpful for hydraulic design of centrifugal pump.     

不同叶轮形式下离心泵整机非定常流场的数值研究

针对无短叶片、有长短叶片和短短叶片三种叶轮的离心泵,采用非定常CFD方法数值分析了设计工况点的整机全三维流场,讨论了不同叶片形式对水泵扬程、进出口压力波动及叶片表面和中央回转面内参数分布的影响。其中,与无短叶片情况相比较,详细分析了短叶片的有无和短叶片尺寸对泵内流场的影响;并对一个压力波动周期内,由于叶片和蜗舌相对位置不同内部流场的变化给出了相应的分析结果。从动力学角度对降低水泵的振动和噪声提供了有益的分析结果。