Investigation into the Interaction of Centrifugal Compressor Impeller and Vaneless Diffuser

Theinteractionofcentrifugalcompressorim pelleranddiffusertakesgreateffectontheperfor manceofcentrifugalcompressor.Researchresults showthatwhentheairflowoutoftheimpellerflows throughthediffuser,theefficiencyofthecompressor maydecreaseby10%orso.Soitcanbeofg…     

径向导叶式多级泵单级叶轮切割的三维数值模拟

为探究径向导叶式压出室离心泵叶轮切割后性能的变化,基于N-S方程、标准k-ε湍流模型和SIMPLE算法对MD-280-42×4多级离心清水泵单级叶轮外径切割进行三维湍流数值计算,分析不同切割量下径向导叶式离心泵外特性和内部流动变化。结果表明:在设计工况(Q_d=0.078 m3/s)下,随着切割量的增加,径向导叶式离心泵的水力效率、轴功率均呈现下降趋势;在相同小流量工况下,随着切割量的增加,叶轮与导叶间隙和反导叶流道处流动损失逐渐减小,水力效率呈现上升趋势;在相同大流量工况下,随着切割量的增加,正反导叶流道流动均匀性受到较严重破坏,产生了较大的能量耗散,水力效率明显下降。       

多段离心压缩机中冷系统优化调节

离心压缩机是一种应用广泛的大型耗能机组 ,它具有运转周期长、功率消耗大等特点。因此如何调节中冷系统使偏离设计工况的机组在其相对的最经济工况点运行 ,对于企业节能 ,提高能量利用率具有重要的意义。在应用欧拉方程、伯努力方程及焓值方程等流体力学及热力学基本方程对多段离心压缩机进行系统分析的基础上 ,建立了以机组运行费用为目标函数 ,以满足排气压力 ,排气温度等工艺要求 ,中冷器冷却能力及压缩机喘振、阻塞等限制条件为约束的有约束非线性的系统优化模型 ;确定了求解方法 ;编制了人机交互界面良好的计算机应用软件。可在不增加任何投资的基础上 ,通过中冷系统的优化调节 ,使机组系统处于相对最优的运行状态。     

风扇级负荷对其进口总压畸变响应特性影响研究

基于不同转子级负荷下的风扇压气机叶排实验特性,应用畸变传递的矩阵分析模型,对不同级负荷下的风扇压气机转子叶排、静子叶排的容进口总压畸变特性进行了详细分析,初步建立了级负荷对总压畸变及其沿轴流压气机叶排衰减特性影响规律。计算结果表明,提高转子级负荷在设计工况附近能有效提高转子叶排容总压畸变能力,但在接近失速工况下其容总压畸变能力明显降低;不同转子负荷下其后静子叶排容畸变特性存在明显差异,这对合理选择风扇压气机设计级负荷尤为重要。     

进口导叶/叶轮/扩压器非定常相干的数值研究

在非零进口导叶预旋角度下,采用非定常的方法对进口导叶/叶轮/扩压器三部件之间非定常相干进行了数值模拟,研究了进口导叶/叶轮/扩压器三部件之间动静相干的机理。结果表明,叶轮由于受进口导叶尾流和扩压器势反冲效应的双重非定常影响,叶轮受非定常影响最小的区域出现在叶片50%弧长附近,最大的非定常影响出现在叶轮和扩压器之间的动静交界面上。当离心压缩机前带有进口导叶预旋时,扩压器受前面两部件的同时影响,扩压器叶片上的非定常变化沿流向比较均匀。     

长短叶片半开式离心叶轮内部流动的数值模拟

为了分析分流叶片对于半开式离心叶轮内部流动的影响，对轴向间隙为1.1 mm的4长叶片和4长4短叶片的两种半开式低比转速高速离心叶轮进行了研究.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了三维紊流数值计算和分析；并对离心泵进行了试验研究.数值计算结果表明，分流短叶片可以改善叶轮内部的流动；两个叶轮内部的静压力都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的；具有分流叶片的叶轮出口的压力系数较高.实验结果表明，具有分流叶片的叶轮离心泵的扬程和效率较高，说明分流叶片可以提高离心泵的性能.     

基于轴向力的离心压缩机级密封的状态预测方法

本文讨论离心压缩机级密封状态的评估问题。根据离心压缩机转子所承受的、可实时监测的轴向力与级密封间隙的关系,提出了基于轴向力的离心压缩机级密封状态的预测方法。在分析叶轮两侧缝隙内泄漏气体流动的基础上,采用计算流体动力学方法对其进行仿真,得到轮盘及轮盖上的压力分布,由此计算出轴向力。把不同级密封间隙值及对应的轴向力作为输出、输入向量,对BP神经网络进行训练,以获得在线状态评估模型。测试结果表明,该模型对离心压缩机级密封的状态预测方法是有效的。     

Development and application of a throughflow method for high-loaded axial flow compressors

In this paper, a novel engineering platform for throughflow analysis based on streamline curvature approach is developed for the research of a 5-stage compressor. The method includes several types of improved loss and deviation angle models, which are combined with the authors’ adjustments for the purpose of reflecting the influences of three-dimensional internal flow in high-loaded multistage compressors with higher accuracy. In order to validate the reliability and robustness of the method, a series of test cases, including a subsonic compressor P&W 3S1, a transonic rotor NASA Rotor 1B and especially an advanced high pressure core compressor GE E³ HPC, are conducted. Then the computation procedure is applied to the research of a 5-stage compressor which is designed for developing an industrial gas turbine. The overall performance and aerodynamic configuration predicted by the procedure, both at design- and part-speed conditions, are analyzed and compared with experimental results, which show a good agreement. Further discussion regarding the universality of the method compared with CFD is made afterwards. The throughflow method is verified as a reliable and convenient tool for aerodynamic design and performance prediction of modern high-loaded compressors. This method is also qualified for use in the further optimization of the 5-stage compressor.     

Numerical investigation of radial inflow in the impeller rear cavity with and without baffle

In typical small engines, the cooling air for high pressure turbine(HPT) in a gas turbine engine is commonly bled off from the main flow at the tip of the centrifugal impeller. The pressurized air flow is drawn radially inwards through the impeller rear cavity. The centripetal air flow creates a strong vortex because of high inlet tangential velocity, which results in significant pressure losses. This not only restricts the mass flow rate, but also reduces the cooling air pressure for down-stream hot components. The present study is devoted to the numerical modeling of flow in an impeller rear cavity. The simulations are carried out with axisymmetric and 3-D sector models for various inlet swirl ratio β_0(0–0.6), turbulent flow parameter lT(0.028–0.280) with and without baffle. The baffle is a thin plate attached to the stationary wall of the cavity, and is proved to be useful in reducing the pressure loss of centripetal flow in the impeller rear cavity in the current paper. Further flow details in impeller rear cavity with and without baffle are displayed using CFD techniques. The CFD results show that for any specified geometry, the outlet pressure coefficient of impeller rear cavity with or without baffle depends only on the inlet swirl ratio and turbulent flow parameter. Meanwhile, the outlet pressure coefficient of the cavity with baffle is indeed smaller than that of cavity without baffle, especially for the cases with high inlet swirl ratio. The suppression of the effect of centrifugal pumping and the mixing beween the main air which is downstream of the baffle and the recirculating flow of the vortex in the stationary cavity, which are caused by the use of baffle, are the underlying reasons that lead to the reduction of outlet pressure loss.     

多级离心泵内部间隙流动与泄漏损失

为研究多级离心泵前后密封口环对整体水力性能和容积损失的影响,以某高压离心泵为分析模型,建立叶轮、导叶和密封环一体化的整体模型并进行了三维流场模拟,得到不同工况下多级泵的水力性能和口环间隙泄漏量,分析间隙内的流场结构.结果表明,考虑环形间隙结构的全模型性能预测结果与试验值取得较好的一致,在设计点附近的泄漏量预测值与经验公式计算结果接近.高压多级离心泵内部泄漏损失对性能存在明显的影响,间隙内的回流和叶片出口处的损失随流量增加而减小,相反地,叶轮入口处的损失因流量和间隙泄漏量增加而增大.     

Aerodynamic effects of impeller-diffuser axial misalignment in low-flow-coefficient centrifugal compressor

A numerical investigation on the aerodynamic effects of impeller-diffuser axial misalignment in the low-flow-coefficient centrifugal compressor is conducted through three-dimensional CFD analysis.The results show that the flow,especially near the diffuser inlet,is influenced by the axial misalignment obviously.When the impeller offsets to one side,the pressure at diffuser inlet close to this side will descend,and the vortex in the cavity on the other side will partially enter the diffuser and then result in the back flow.The performances of the stage and its components also change with the impeller-diffuser axial misalignment.There exists an optimum offset making the efficiency maximum at a given operating point.Furthermore,the effect of impeller-diffuser axial misalignment on the axial thrust is pronounced.The axial thrust is nearly increased linearly with the increase of axial misalignment.The aerodynamic effects of impeller-diffuser axial misalignment in the low-flow-coefficient centrifugal compressor behaves more remarkably at the large flow rate.To alleviate the aerodynamic effects of impeller-diffuser misalignment,a rounding in the meridional plane at the diffuser inlet can be applied.     

二级增压系统中高压级压气机性能研究

为使高低两级压气机达到优化匹配,提高整个二级增压系统的效率,在二级增压系统试验台架上对高压级压气机的性能进行了研究。通过在增压系统中,使新鲜空气首先通过低压级压气机进行预压缩,提高其温度和压力,从而得到高压级压气机的高温高压进口条件。在两级压气机之间设置中冷器,使每一条等转速曲线,高压级压气机进口温度保持不变。试验结果表明,由于进口温度提高,压气机折合转速与实际转速相差较大,为达到预定压比,必须进一步提高压气机转速;进口压力大幅度提高是造成高压级压气机折合流量偏小的主要原因;为避免高压级压气机发生喘振,应控制高压级压气机的进口压力。     

Investigation of the spike-stall warning method using the blade passing signal

The vaned-diffuser usually brings compressor instability problems under the small flow rate, for instance the spike-type rotating stall phenomenon which restricts the operation range and may cause the trouble of blade fatigue. Since it is difficult to mathematically predict the spike-type stall for its randomness, finding out a practical method to warning this stall precursor appears to be meaningful. The paper explains the relationship between the spike-type precursor and the blade passing irregularity coefficient to analyze whether this coefficient is appropriate for the spike-stall warning inside a centrifugal compressor with the vaned-diffuser. The advanced wireless measurements were conducted on a 1.5 stages test centrifugal compressor to capture the unsteady behavior progressing from the design to stall inception within the region between the impeller trailing edge (TE) and diffuser leading edge (LE). The circumferential distribution of the blade passing irregularity has been quantitatively revealed. The steep increase of the blade passing irregularity at some “special locations”, which is responsible for the onset of the spike-type precursor, is highlighted. Also, to further understand the spike precursor inside the diffuser passage corresponding to the circumferential “special location” with maximum irregularity, the high-response transient measurement within this passage is presented. With the help of full-annulus computational fluid dynamics (CFD) simulation and the mathematical model, it is proved that the blade passing irregularity precisely reflects the flow characteristics during the spike precursor, which presents the guidance for this stall warning method.     

利用轴向力预测离心压缩机的级密封状态

根据离心压缩机转子所承受的、可实时监测的轴向力与级密封间隙的关系,提出了基于轴向力的离心压缩机级密封状态的预测方法.在分析叶轮两侧缝隙内泄漏气体流动的基础上,采用计算流体动力学方法对其进行仿真,得到轮盘及轮盖上的压力分布,由此计算出轴向力.把不同级密封间隙值及对应的轴向力作为输出、输入向量,对BP神经网络进行训练,以获得在线状态预测模型.测试结果表明,该模型对离心压缩机级密封的状态预测是有效的.     

Anti-cavitation performance of a splitter-bladed inducer under different flow rates and different inlet pressures

The anti-cavitation performance of a high-speed centrifugal pump with a splitter-bladed inducer is investigated under different flow rates and different inlet pressures. Simulations and external characteristics experiments are carried out. Static pressure and the vapor volume fraction distributions on the inducer and the impeller of the pump under various operation conditions are obtained. The results show that the cavitation developments on the impeller and on the inducer with the flow rates are reverse, while the development of the inlet pressure on the inducer and the impeller is the same. Cavitation on the impeller increases with the increase of flow rates, and it extends to the near passages with rotating, while cavitation on the inducer is more complex than that on the impeller. Cavitation at the inlet of the inducer decreases with the increase of flow rates, while cavitation at the outlet of the inducer is opposite. The results also show that cavitation development on the impeller and on the inducer with the inlet pressure is the same. Cavitation both decreases with the increase of the inlet pressure at the same flow rate. Furthermore, asymmetric cavitation on the impeller and on the inducer is both observed. And the asymmetric degree of cavitation on the impeller is higher than that on the inducer.     

离心叶轮入口流动的动力学描述

在实验的基础上用动力学理论对离心叶轮机械入口的复杂流动进行了研究．把离心叶轮入口流动看成是保守系统,在此基础上建立了理想流动的自治系统．在相平面内初步讨论了离心叶轮入口流动的结构及其一些重要特性．     

离心泵部分负载下进口二次回流成因分析及验证

为探讨离心叶轮在部分负载下进口回流的成因以及其对离心泵运行的影响,应用理论分析与实验方法对强制涡压力分布特点、叶轮入口二次回流产生的原因进行分析,采用数值模拟方案对一比转速为66的泵进行数值计算,探讨在不同流量下叶轮进口速度与压力分布规律,对比叶片进口切割前后的泵外特性,分析入口回流对泵外特性的影响。结果表明:强制涡中压力随着半径增大按抛物线规律上升;二次回流产生的原因在于部分工况下旋转叶轮形成叶轮入口黏性流体的强制涡产生不同半径上的压力差,回流对消除流量扬程曲线的驼峰有积极作用。本文对离心泵部分负载下进口回流成因的探讨以及深入认识离心泵流动原理提供了一定的参考。     

低比转速离心泵驼峰稳定性及其影响因素研究

为了提高低比转速离心泵的效率,一般会将叶轮叶片出口角加大一些,但会引起H-Q曲线有驼峰,导致泵在小流量区运行不稳定.本文以国内某水泵厂生产的比转速为47的单级单吸式离心泵为研究对象,采用正交试验法选择叶轮出口边斜切比、出口角度、叶轮轴线倾斜角度、叶片包角、叶片进口边位置5个因素,每个因素采用4个水平,一共16个叶轮设计...     

节段式多级离心泵全三维湍流场的数值模拟

选取工业中常用的DF型多级离心泵作为研究对象,数值计算使用了FLUENT软件及其RNG k-ε湍流模型和多重参考坐标系,实现了节段式多级离心泵任意一整级（包括叶轮导叶在内）的全三维流场的数值模拟.模拟结果显示在叶轮出口与导叶入口衔接处,叶轮出流因受到导叶叶片头部的阻挡干扰,导致局部流体逆叶轮旋转方向运动.液流的静压值在正导叶出口附近达到泵级内最大值,进入反导叶后因沿程出现的水力损失静压值略有降低.计算结果得到了泵外特性实测值的验证.     

基于大涡模拟的导叶式混流泵叶轮内压力脉动特性分析

为研究导叶式混流泵叶轮内部非定常压力脉动特性,在其叶轮进口截面及出口截面附近分别设置8个压力脉动监测点,采用大涡模拟方法(LES)对导叶式混流泵内全三维流道(进水管、叶轮、导叶及出水管)进行模拟,并对8个监测点进行压力脉动时域图和频域图的分析。结果表明:由于旋转叶轮旋转失速、脱流效应及静止导叶的干涉作用,叶轮出口处压力脉动系数幅值均大于进口处脉动系数幅值,且其最大压力脉动发生在叶轮出口处,脉动波衰减较慢;叶轮进、出口截面上监测点的压力脉动频率以叶轮叶频为主频次,且压力脉动主要频率为叶频的倍数。