高马赫数离心压缩机模型级叶轮叶型优化

应用NUMECA软件对Mu2=1.21的高马赫数离心压缩机模型级在设计工况下进行三维流动数值模拟。分析叶轮内部流场时发现,叶轮叶片出口吸力面处流动发生分离并伴随有较大的旋涡,且在叶顶处尤其明显。这一现象增加了流动损失,导致模型级效率以及工作范围达不到要求。针对这一问题,提出了改进措施。应用NUMECA流体分析软件中的AUTOBLADE和DESIGN3D模块,对叶轮叶片中弧线型线进行调节改进。改进后叶轮流动中的分离与旋涡现象消失,且叶轮等熵效率在设计工况下增加了4.58%,模型级变流量工作范围也扩大了5.83%,从而满足了设计性能的要求。结果表明,控制叶轮叶片型线角度分布,可以有效地改善叶轮流场,消除近壁面分离和旋涡现象,从而提高整级的性能。     

流体机械离心叶轮出口流场控制技术研究

流体机械离心叶轮的内部流场复杂,其内部出现的二次流会导致叶轮出口的压力和速度分布不均匀,致使叶轮效率降低,同时恶化后续元件的进口流场,使整机性能下降。本文提出了一种优化离心叶轮出口流场的新技术叶片后段开孔法;并以9-19离心风机为算例,探索此法提高整机效率和压力的可行性。数值计算结果表明,叶片后段开孔法将离心风机设计流量和小流量区的效率提高了1%-2％,同时压力也略有提高,效果明显。流场分析表明,叶片后段开孔法可以有效改善叶轮的流场结构,减少了流动损失,提高了离心叶轮的效率。     

离心泵偏置短叶片叶轮内部流动的粒子图像速度测量

对三副短叶片不同偏置的低比转数复合叶轮离心泵,应用粒子图像速度仪分别测试大流量、设计流量和小流量三种工况下长短叶片叶轮同一叶槽内的瞬时流场.分析叶槽内相对速度矢量、速度等值线的特征,揭示短叶片不同偏置时的速度分布规律.研究三副长短叶片复合叶轮出口处径向速度、切向速度、相对速度和相对液流角沿圆周的分布,测得与三副叶轮相对应的泵外特性曲线.测量结果表明,分流短叶片不同偏置对叶槽内流场的影响差异明显,当短叶片进口相对出口向压力面偏转时,叶轮出口相对速度分布很不均匀,短叶片工作面出口存在较大的低速区;与之相反,当短叶片进口相对出口向吸力面偏转时,叶轮出口速度分布较均匀,并且泵的扬程与流量曲线明显右移,大流量时,效率显著提高.     

叶片仿鲨鱼鳍的导叶式离心泵数值仿真研究

针对导叶式离心泵内部流场流动不稳定的问题,运用仿生学技术和原理对鲨鱼鳍结构做了适当抽象处理,并运用在导叶式离心泵叶轮叶片前缘位置。对叶片仿鲨鱼鳍的导叶式离心泵内部流场进行了数值计算,研究了3个典型工况下离心泵内部流场的流动特性,得到了叶轮和导叶径向力的变化特性,进而分析了离心泵内部流场的湍动能分布规律,并进行了试验验证。研究结果表明:相比原模型,叶片仿鲨鱼鳍的导叶式离心泵改善了泵内流动特性,减小了泵内的湍动能分布;同时降低了叶轮和导叶的径向力,减弱了叶轮与导叶的动静干涉作用;仿鲨鱼鳍叶片减轻了导叶式离心泵内部流动的不稳定,明显提高了泵的扬程和效率等外特性参数。     

组装式压缩机叶片扩压器设计及性能分析

针对某组装式压缩机用半开式小流量系数叶轮,设计了两种不同型式的叶片扩压器,并对半开式叶轮和叶片扩压器组成的模型级的内部流动进行数值模拟,以及对两种扩压器的流场分布和性能进行了分析。试验结果表明:采用机翼形扩压器相比楔形扩压器,气动性能得到明显提高。     

长短叶片离心泵汽蚀性能数值模拟分析及实验研究

为提高离心泵的汽蚀性能,利用CFD数值模拟分析与实验研究相结合的方法对长短叶片离心泵在不同汽蚀余量时叶轮内部气液两相的分布规律进行分析研究,分析了3种不同短叶片进口直径在不同汽蚀工况时气泡分布情况对叶轮内部流动和性能的影响。分析结果表明:选择合理短叶片的进口直径可以有效提高离心泵的抗汽蚀性能,避免叶轮进口堵塞和流道内发生漩涡汽蚀。当汽蚀余量减小到一定程度,离心泵短叶片进口直径为0.65D2(D2为叶轮外径)时,在长叶片和短叶片的背面都会出现漩涡汽蚀区;当离心泵短叶片进口直径为0.75D2时,在长叶片背面与短叶片工作面间的流道内会出现两个漩涡汽蚀区;当离心泵短叶片进口直径为0.85D2时,离心泵的抗汽蚀性能最佳。     

高转速大小叶片斜流叶轮数值模拟

用数值模拟方法对高压比大小叶片斜流式叶轮内部全三维有粘流场进行了详细分析,获得该压缩机的特性曲线和主要参数分布。计算结果表明,设计点达到设计要求值,斜流叶轮内部流动正常,满足性能要求,叶轮的小叶片在气流通道后部还有一定的改进余地。     

分流叶片周向位置对离心叶轮性能及内部流动的影响

利用商用计算流体力学软件包NUMECA FINE/TURBO对Krain叶轮内部三维粘性流场进行了数值模拟研究。重点分析了分流叶片不同周向位置对该叶轮内部流动和性能的影响,得出了不同周向位置时的叶轮效率、压比随质量流量变化关系,结合对叶轮内部流场的详细分析,给出了适合此半开式离心叶轮分流叶片周向位置的最佳设计方案。研究结果表明:分流叶片不同周向位置对叶轮流道流场影响明显,当偏向主叶片吸力面一侧时可以有效提高叶轮效率。     

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。     

基于ANSYS CFX旋涡泵的数值模拟

旋涡泵内部流动比较复杂,为了更好的约束旋涡泵内部流体的运动,提高旋涡泵的效率,文中设计了5种不同形状的叶轮,通过ANSYSCFX对流动区域进行网格划分,采用基于雷诺时均方程的RNG k-ε湍流模型对不同叶片形状的旋涡泵内部流场进行了数值模拟。研究分析了旋涡泵内部压力场和速度场的分布情况,提出了采用全圆弧转弯叶轮的旋涡泵效率比较高的观点,对优化旋涡泵结构有一定的参考价值。     

离心压缩机二元和三元叶轮内流分析

选择两个不同相对轴向尺寸和相对宽度的叶轮,在各自子午型线保持不变的情况下,分别对每一个叶轮构造普通圆弧叶片和三元扭曲叶片。利用Ｓ１,Ｓ２流面理论简化计算模型对所构成的具有不同叶片形式的叶轮进行了内部流场计算。着重对比了叶片表面的速度分布,对其起因进行了分析讨论。     

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.     

The vibration behavior of impeller blades in the five-axis CNC flank milling process

Today, in most cases, impellers of centrifugal compressors are produced by flank milling on five-axis CNC milling machines. The complex three-dimensional geometry of the very thin blades consists of ruled surfaces. The flank milling process allows a fast production of the impellers and the surface of the blades is of high quality. The limited strength of the very thin blades and also the thin outer radial part of the disk lead to a high sensitivity to static and especially dynamic forces that are caused by the instationary flow in the impeller. The dynamic forces of rotating stall and surge are the most dangerous excitations of the bladed disk. Coupled vibrations may occur and damage the impeller. The highest static load is caused by the centrifugal forces. Therefore, most of the high-loaded impellers are manufactured from aluminum alloy or titanium because of the low density of this light metals and the relatively high strength. Most of the interests and the investigations in the last years are paid to the vibration behavior and the dynamic loads of the impeller during operation. But sometimes, the highest stress may occur during the production process and damage the impeller or weaken the strength and so cause later problems. Especially, excitations from the dynamic forces during the flank milling process have to be taken under consideration. The vibration behavior of the impeller is very complex and is affected by the vibration behavior of the cutter and the milling machine. In this paper, the change of the vibration behavior of centrifugal compressor impeller blades during the manufacturing process is investigated. During the finishing of the thin blades, the blade thickness is continuously changing and also the strength and the corresponding eigenfrequencies of the blade. The dynamic forces acting on the blades are caused by the cutter, the milling machine, and the cutting process. The quantity of the forces and the frequency of the excitation are determined by the rotational speed of the cutter, the feed, the number of edges, and the chip thickness. The results described in this paper give useful information about the change of the vibration behavior of the centrifugal impeller blades during the flank milling process and possible interaction with the cutter and the machine.     

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。     

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.     

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.

     

带分流叶片低比转速无过载离心泵优化设计

针对TS65-40-250离心泵易过载和出现驼峰等问题,采用无过载设计法并添置分流叶片,重新选取叶轮设计参数,设计3种优化方案。采用Pro/E和ICEM分别对3种方案进行三维造型和结构化网格划分,网格总数为150万。利用商业软件CFX12.1对优化方案进行数值模拟,边界条件设定为速度进口、压力出口和无滑移壁面。采用标准k-ε模型,预测了3种方案下的外特性,分析了不同设计方案下叶轮内的压力、流线、湍动能、速度分布。通过数值模拟,得出叶轮1的水力性能和内部流动状态均较好。利用快速成型法加工叶轮1并进行试验。试验结果表明,叶轮1扬程最高高出设计参数的15%,试验效率高于国家标准2%～6%,而且有很好的无过载性能。模拟结果和实验结果表明,采用无过载设计并添置分流叶片优化方法是可行的,这种设计方法可以为低比转速无过载离心泵优化设计提供参考。     

PERFORMANCE CHARACTERISTICS AND VISCOUS FLOW ANALYSIS OF CENTRIFUGAL PUMPS

ＰＥＲＦＯＲＭＡＮＣＥＣＨＡＲＡＣＴＥＲＩＳＴＩＣＳＡＮＤＶＩＳＣＯＵＳＦＬＯＷＡＮＡＬＹＳＩＳＯＦＣＥＮＴＲＩＦＵＧＡＬＰＵＭＰＳＰＥＲＦＯＲＭＡＮＣＥＣＨＡＲＡＣＴＥＲＩＳＴＩＣＳＡＮＤＶＩＳＣＯＵＳＦＬＯＷＡＮＡＬＹＳＩＳＯＦＣＥＮＴＲＩＦＵＧ...     

Particle image velocimetry in a centrifugal pump: Details of the fluid flow at different operation conditions

Centrifugal pumps are present in the daily life of human beings. They are essential to several industrial processes that transport single- and multi-phase flows with the presence of water, gases, and emulsions, for example. When pumping low-viscous liquids, the flow behavior in impellers and diffusers may affect the centrifugal pump performance. For these flows, complex structures promote instabilities and inefficiencies that may represent a waste of energetic and financial resources. In this context, this paper aims at characterizing single-phase water flows in one complete stage of a centrifugal pump to improve our understanding of the relationship between flow behavior and pump performance. For that, a transparent pump prototype was designed, manufactured and installed in a test facility, and experiments using particle image velocimetry (PIV) were conducted at different conditions. The acquired images were then processed to obtain instantaneous flow fields, from which the flow characteristics were determined. Our results indicate that the flow morphology depends on the rotational speed of the impeller and water flow rate: (i) the flow is uniform when the pump works at the best efficiency point (BEP), with streamlines aligned with the blades, and low vorticity and turbulence in the impeller; (ii) the velocity field becomes complex as the pump begins to operate at off-design conditions, away from BEP. In this case, velocity fluctuations and energy losses due to turbulence increase to higher numbers. Those results bring new insights into the problem, helping validate numerical simulations, propose mathematical models, and improve the design of new impellers.     

Parametric study on a forward-curved blades centrifugal fan with an impeller separated by an annular plate

A parametric study on the geometry of an impeller in a forward-curved blades centrifugal fan for residential ventilation has been carried out in this work. Numerical analysis of a forward-curved blades centrifugal fan was carried out by solving three-dimensional Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model. A validation of numerical results was conducted by comparison with experimental data for the pressure and efficiency. The impeller separated by an annular plate was employed, and the annular plate height and the angle between the upper and lower impellers were selected as the geometric parameters to investigate their effects on the efficiency of the forward-curved blades centrifugal fan. Additionally, the impeller geometry having the highest efficiency was tested with the number and exit angle of blades. The results show that the impeller with properly installed annular plate improves the aerodynamic performance of the forward-curved blades centrifugal fan.