基于CFD技术的旋流泵优化设计与试验研究

为了提高旋流泵的扬程与效率,基于雷诺时均Navier-Stokes方程和标准k-ε湍流模型,应用三维无结构四面体网格及Simplec算法,利用计算流体力学软件Fluent对3种不同高度差叶片旋流泵的水力性能进行了数值模拟,得到其内部流场的速度分布和压力分布情况,揭示了旋流泵在不同叶片高度时的运动规律,并对数值模拟结果进行了试验验证.结果表明:旋流泵内部存在较强的纵向旋涡和轴向旋涡,高低叶片可以改善旋流泵内部的流动情况,提高旋流泵的扬程与效率.试验研究证明了模拟结果的正确性,当旋流泵叶片的高度相差8%左右时,扬程提高0.15 m,效率提高约3%.     

采用开缝叶片流动控制的低比转速离心泵数值模拟与试验研究

基于流动控制技术,以某型号的低比转速离心式不锈钢冲压叶轮作为研究模型,采用数值模拟和试验研究了叶片不同开缝位置(r/R)对叶轮内部能量、湍流动能及耗散率分布的影响,同时制作了开缝叶片离心泵样机模型,并进行了试验验证,分析了叶片上开缝的相对位置对离心泵的扬程及效率等外特性的影响,比较了叶片有、无开缝的性能变化。研究结果表明:叶片开缝的位置对叶轮内流体能量的分布以及获得的总压能影响较大;开缝的存在会引起离心泵内部流场的变化,在开缝的地方会产生湍动能及耗散率的突变;不同的开缝相对位置对离心泵性能影响不同,开缝的相对位置为0.875,与没有开缝叶片的离心泵相比,效率提高了1.52%,拓宽了离心泵的高效区间,在大流量时,开缝存在起到了抑制分离的产生,提高了离心泵的扬程,改善了叶轮流道中流体的流动状态。     

偏心度与间隙比对轴流泵流动激励力的影响

叶轮偏心将会引起轴流泵叶轮顶部间隙沿周向不均匀,从而导致附加的流动激励和噪声.利用计算流体力学商业软件Fluent模拟不同偏心度和间隙比的轴流泵非定常流场,研究周向非均匀间隙对泵内压强脉动及叶轮激励力的影响.结果表明:壁面压强脉动强度并不是在最小间隙处达到最大,而是出现在偏离最小间隙处约30°~60°的方向,并随着间隙比增大,脉动强度最大值发生位置逐渐向最小间隙处靠拢;同时,偏心造成的非均匀叶顶间隙引起了轴频处的压强脉动,在间隙比为2.5%下偏心度从0%增加到60%,轴频处的压强脉动相对增量为661.54%;叶轮受到的径向激励力时均值与偏心度呈线性关系,其斜率与间隙比的平方根成正比.     

轴流泵内部流动诱导噪声数值研究

为改善轴流泵运行的稳定性,采用CFD方法和Lighthill声比拟理论,利用CFX对模型泵在0.55Q_(BEP)、0.6Q_(BEP)、0.9Q_(BEP)、Q_(BEP)、1.1Q_(BEP)流量下的轴流泵内部流场进行非定常模拟,并基于CFX数值模拟所得到的流动信息,根据FW-H方程提取叶片表面偶极子声源,并在LMS Virtual.Lab中采用内外声学直接边界元模型计算不同工况下的模型泵内叶频及其谐频处的内声场。研究结果表明,泵内边界上最大声压值随着流量的减小逐渐增大;叶片偶极子噪声在叶频96Hz处的深度失速工况泵内边界声压比最优工况下增大了28.9%;壳体偶极子噪声在轴频24Hz处的深度失速工况泵内边界声比最优工况下增大了6.5%,在叶频96 Hz时的深度失速工况泵内边界声压高于最优工况7%。     

添加剂对CO_2水合物浆流动特性的影响

搭建了研究水合物浆生成、流动、传热特性的实验系统,对添加TBAB、TWEEN两种防聚剂的CO_2水合物浆与纯水系中的CO_2水合物浆进行比较,从而筛选出流动特性最好的防聚剂种类及其对应的质量分数.结果发现,添加TBAB和TWEEN后能有效阻止水合物聚集成团,提高了浆体的稳定性和均匀性.研究表明:当流速为0.2~0.4 m·s~(-1)时,浆体表现为H-B流体,呈剪切变稀特性;当流速为0.4~0.6 m·s-1时,TBAB质量分数分别为0.3%、0.9%和TWEEN质量分数为0.6%时浆体均表现为宾汉姆流体,呈剪切变浓特性,其余质量分数时浆体与低流速区相似,均表现为H-B流体,呈剪切变稀特性.提高TBAB质量分数,对改善CO_2水合物浆流动效果明显,而当TWEEN质量分数为0.6%时浆体的流动特性最好.     

叶片包角对高比转速离心泵固液两相流动的影响

为研究叶片包角对高比转速离心泵固液两相流动的影响,采用Mixture多相流模型,利用CFX软件对5种不同叶片包角的高比转速离心泵进行了固液两相湍流数值模拟,分析了固液两相流中固体体积分数分布及速度变化规律。研究表明:在2%的泥沙含量条件下,随着叶片包角的增加,效率有所下降,叶片包角φ=100°时效率最优;颗粒主要分布在叶轮后盖板及叶片背面尾部;固体速度在距后盖板的0.7位置及叶片头部位置达到最大;随着包角的增大,叶轮流道内的压力在减小,后盖板、叶片背面尾部的颗粒浓度明显降低,流道和叶片上的固体速度会增加;颗粒浓度下降速度快慢的临界点在距离后盖板0.15处;叶片背面颗粒浓度的峰值点出现在叶片长度为0.9处,此时,φ=110°时的颗粒含量受到包角的影响最大;综合颗粒体积分数及固相速度的分布规律,适当增大叶片包角使得效率降低,但可改善固液两相流离心泵后盖板及叶片背面磨损情况。     

轴流泵内气液两相流动的数值模拟

为进一步揭示轴流泵的气液两相流动的一般规律,基于ANSYS软件对轴流泵的气液两相流动三维流场进行数值计算与分析,研究了叶轮及出口导叶的压力面和吸力面的静压分布及气泡体积分布情况。结果表明,叶轮流道内,同等气泡体积分数下,当气泡粒径增大时,压力面上的气泡会由叶片出口处向着靠近轮毂处减少;而吸力面上的气泡会由进、出口处向着叶片中部靠近轮毂处聚集。气泡粒径不变时,当气泡体积分数增大时,叶片压力面上的气泡会由进口及轮缘处向着出口靠近轮毂处聚集;而吸力面上的气泡会由进、出口处向着叶片中部靠近轮毂处聚集。导叶流道内,同等气泡体积分数下,当气泡粒径增大时,叶片压力面上的气泡会由出口及轮缘处向着进口靠近轮毂处聚集,出口靠近轮缘处气泡越来越少;而吸力面上的气泡会由叶片进、出口向着叶片中部慢慢扩散。气泡粒径不变时,当气泡体积分数增大时,压力面上的气泡会由进口靠近轮毂处向着出口靠近轮缘处扩散;而吸力面上的气泡会由叶片进、出口向着叶片中部扩散。     

可调向心涡轮蜗壳流动周向非均匀性的研究

针对某可调向心涡轮增压器,基于蜗壳流动周向非均匀性的分布规律,提出采用改进喷嘴座连接臂结构和非均匀布置可调导叶的设计方案,以降低涡轮级各部分的流动损失,提高涡轮效率.结果表明:改型后涡轮工作在发动机标定功率工况对应相似转速条件下效率相对提高值最大为5.18%,,发动机最大转矩工况对应相似转速条件下效率相对提高值最大为3.57%,;改型后蜗壳出口气流角变得更加均匀,蜗壳出口气流角与导叶开度角相接近,减小了喷嘴环区域的流动损失,解释了改型前、后涡轮效率提高的原因;改型后各叶轮流道流量的周向非均匀性明显降低,各叶轮叶片负荷周向分布更加均匀.证明改型方案对提高涡轮效率,降低叶片振动,延长涡轮有效使用寿命具有积极的影响.     

非同步动叶周向分布关系对轴流引风机性能的影响

为研究风机叶片发生非同步对风机运行的影响,以SAF36-25-2轴流式引风机为例,应用流场仿真软件FLUENT获得了相间对称分布、两两相间分布、两两对称分布和相邻分布4种叶片安装角发生正反向同等程度偏离情况下引风机的运行特性及流场特征。研究表明:叶片非同步将对风机通道内的流场产生极大的影响,正向偏离时,旋涡出现在非同步叶片旋转方向下一叶片流道内,反向偏离时,旋涡出现在非同步叶片对应的叶片流道内;动叶相间对称分布位置正向偏离引风机效率降低7.7%,反向降低5.8%,相邻分布位置正向偏离引风机效率降低7.2%,反向降低3.0%,相间对称分布位置周向分布对引风机流动效率的影响相对较大;动叶开度正向偏离时平均效率下降可达7.4%,反向偏离时平均效率下降可达4.85%,相对于叶片开度反向偏离,正向偏离产生的不利影响更为明显。     

轴流压气机叶型的类 形函数表述方法及气动优化

利用分析函数表示叶型中弧线与厚度分布,结合准三维流动求解器以及序列二次规划算法对高负荷级的动叶和静叶进行了以减小落后角和气动损失为目标的气动优化。初始叶型为NACA 65叶型,中弧线采用广义抛物线表示,只用最大拱度和最大拱度位置控制;厚度分布采用一阶类/形函数表示,只用一个比例因子KR控制。叶型几何只用3个参数变量,实现对初始叶型的表达。优化后动叶和静叶设计点损失分别下降19%和7.4%,工作范围均有增加,静压比提高,优化叶型的气动分布符合可控扩散叶型的设计思想。     

Effect of Impeller Geometry and Tongue Shape on the Flow Field of Cross Flow Fans

Experiments were conducted to investigate the effect of impeller geometry and tongue shape on the flow field of cross flow fans. Three impellers (Ⅰ,Ⅱ,Ⅲ) having same outer diameter, but different radius ratio and blade angles were employed for the investigation. Each impeller was tested with two tongue shapes. Flow survey was carried out for each impeller and tongue shape at two flow coefficients, and for each flow coefficient at different circumferential positions. The flow is two-dimensional along the blade span except near the shrouds. The total pressure developed by the impellers in each case is found to be maximum at a circumferential position of around 270°. The total and static pressures at the inlet of impellers are more or less same regardless of impeller and tongue geometry, but they vary considerably at exit of the impellers. Impeller Ⅲ with tongue T2 develops higher total pressure and efficiency where as impeller Ⅱ with tongue T2 develops minimum total pressure. Higher diffusion and sma     

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.     

双吸泵空化非定常数值分析

为了分析双吸泵内部非定常空化流,采用SST湍流模型及基于Rayleigh-Plesset方程的输运空化模型,对双吸泵空化流场进行定常与非定常模拟,得到了双吸泵内流场空化初生部位及空化发展情况,并设置监测点分析了空化状态下双吸泵内不同位置处的压力脉动特性。结果表明,空化首先发生于叶片吸力面头部靠近前盖板处,随着空化余量的降低,空化面积及空泡体积分数不断增大,空化继续发展后,空泡会逐渐向叶片吸力面及叶轮出口扩散,从而降低泵的扬程;在一个旋转周期内,单个叶片上的空化状态呈现出由弱变强、再由强变弱的发展趋势;随着空化余量的降低,监测点处压力脉动幅值增加,蜗壳流道内压力脉动的主频为叶频,谐频为叶频的倍数,且蜗壳隔舌处的压力脉动幅值最大。     

特低扬程双向立式轴流泵装置水动力特性数值计算

为了研究特低扬程双向立式泵装置的水动力特性,采用数值模拟与模型试验相结合的方法,分析了某特低扬程双向泵装置及过流部件在不同工况下的水动力特性。结果表明,该特低扬程双向立式泵装置及过流部件在设计工况时可获得较为理想的内、外特性;设计工况下泵装置的效率可达70%以上;最高扬程附近运行时,导叶叶道内出现流动分离等不良流态,转轮叶片工作面与背面压差较大,应避免在最高扬程附近运行。     

Experimental analysis of flow structure in contra-rotating axial flow pump designed with different rotational speed concept

As a high specific speed pump, the contra-rotating axial flow pump distinguishes itself in a rear rotor rotating in the opposite direction of the front rotor, which remarkably contributes to the energy conversion, the reduction of the pump size, better hydraulic and cavitation performances. However, with two rotors rotating reversely, the significant interaction between blade rows was observed in our prototype contra-rotating rotors, which highly affected the pump performance compared with the conventional axial flow pumps. Consequently, a new type of rear rotor was designed by the rotational speed optimization methodology with some additional considerations, aiming at better cavitation performance, the reduction of blade rows interaction and the secondary flow suppression. The new rear rotor showed a satisfactory performance at the design flow rate but an unfavorable positive slope of the head-flow rate curve in the partial flow rate range less than 40% of the design flow rate, which should be avoided for the reliability of pump-pipe systems. In the present research, to understand the internal flow field of new rear rotor and its relation to the performances at the partial flow rates, the velocity distributions at the inlets and outlets of the rotors are firstly investigated. Then, the boundary layer flows on rotor surfaces, which clearly reflect the secondary flow inside the rotors, are analyzed through the limiting streamline observations using the multi-color oil-film method. Finally, the unsteady numerical simulations are carried out to understand the complicated internal flow structures in the rotors.     

The effect of radial temperature gradient and axial magnetic field on the stability of couette flow: The narrow gap problem

A numerical solution to the MHD stability problem for dissipative Couette flow in a narrow gap is presented under the following conditions: (i) the inner cylinder rotating with the outer cylinder stationary, (ii) corotating cylinders, (iii) counter-rotating cylinders, (iv) an axially applied magnetic field, (v) conducting and nonconducting walls, and (vi) the presence of a radial temperature gradient. Results for the critical wave number a_c, and the critical Taylor number T_c, are presented. The variation of T_c is shown on graphs for both the conducting and nonconducting walls and for different values of ±μ (= Ω₂/Ω₁, where Ω₂ is the angular velocity of the outer cylinder, and Ω₁ is the angular velocity of the inner cylinder), the magnetic field parameter Q, which is the square of the Hartmann number and ± N (= Ra/Ta, where Ra is the Rayleigh number). The effects of ±μ, N and Q on the stability of flow are discussed. It is seen that the effect of the magnetic field is to inhibit the onset of instability, this being more so in the presence of conducting walls and a negative temperature gradient.     

结构参数对混流式循环水泵性能影响的数值模拟

在混流泵的设计改造中,常用方法是改变叶片的进出口角、改变进口边以及叶轮外径的切削。这些结构参数的改变,也改变了泵的性能。保持泵蜗壳和叶轮外形尺寸不变,改变叶片进出口角的大小、调节进口边、适当切削叶轮外径,设计出一系列的泵,并借助于FLUENT软件模拟泵的内部流场,然后,改变工况求得对应流量的扬程,从而绘制出结构参数改变时对应的泵性能曲线,总结结构参数变化对性能曲线影响的规律。     

基于响应面法的圆盘泵叶轮优化研究

为了提高圆盘泵的水力性能,以径向直叶片圆盘泵为研究对象,结合计算流体动力学方法(CFD)与响应面分析法,研究叶轮结构参数对泵扬程和效率的影响.以叶片高度、叶片数量和盘间距为优化设计变量,泵的扬程和效率为响应变量,基于Box-Behnken样本点设计法进行三因素三水平设计,建立17组样本点.通过ANSYS CFX数值计算...     

Cavitation in semi-open centrifugal impellers for a miniature pump

Cavitation in miniature pumps was investigated experimentally for two semi-open centrifugal impellers. Although both impellers had the same blade cross-section, one impeller had a two-dimensional blade, while the other had a leaned blade. The flows were also analyzed using a numerical model of the three-dimensional turbulent flow in the pumps near the peak efficiency point using the k-ɛ turbulence model and the VOF cavitation model. The average cavitation performance of each impeller was satisfactorily predicted by the numerical simulations. The results show that the miniature pumps have similar cavitation performances as an ordinary-size pump, with the cavitation performance of the semi-open impeller reduced by increased axial tip clearances. Also, both the hydraulic and cavitation performance of the semi-open impeller were improved by the leaned blade. The results also show that uniform flow upstream of the impeller inlet will improve the cavitation performance of a miniature pump. __________ Translated from J Tsinghua Univ (Sci & Tech), 2006, 46(8): 1451–1454 [译自: 清华大学学报(自然科学版)]     

含砂水对混流泵过流部件磨损的数值模拟

为了分析含砂水介质通过混流泵时的流场特性及叶片磨损情况,基于UG软件对混流泵进行建模并利用ICEM软件对其进行网格划分,使用CFX软件对含砂水两相流介质通过混流泵时的内部流场进行模拟分析。结果表明:混流泵磨损主要集中在叶轮叶片和空间导叶处,而且在叶片进口处容易出现磨蚀现象;混流泵扬程随流量增大而减小,效率随流量先增大后减小,且混流泵输送含砂水效率低于输送清水效率。