离心压气机优化设计与流场仿真分析

采用正问题设计方法设计了一个压比为4.2的离心压气机模型。根据压缩系统边界条件约束,首先进行了一维计算,获取叶轮的轮廓图,然后采用参数化建模方法建立了含分流叶片的三维模型,运用CFX软件对不同叶片稠度下的叶轮气动热力学进行了对比数值计算,分析叶轮内部流场及其性能,最终选定9叶片的叶轮为最佳方案。在扩压器的设计方面,提出了一种叶片高度逐渐增加的有叶扩压器模型,并使用CFX对设计的扩压器模型与普通的扩压器进行了数值计算,定量分析其扩压机理及其总压损失特性,计算结果表明所设计的扩压器扩压效果明显优于普通的扩压器。所得结果可为离心式压气机的气动设计提供理论参考。     

无叶扩压器内的射流-尾迹型扰动分析

假设扩压器内部流动为不可压缩的二维流动,采用小扰动方法建立了无叶扩压器的状态矩阵模型,并利用文献中数据对扩压器进口的射流一尾迹型扰动进行了分析.结果表明:径向速度扰动衰减比切向速度快;径向速度扰动衰减的快慢主要受进口流量的影响,进口相对流动角对其影响不大;叶轮叶片数对扰动衰减也有一定影响,叶片数越多,沿径向的速度扰动和角动量衰减就越快;叶轮和有叶扩压器之间的无叶空间可能是引起压缩机失稳的关键因素.模型分析和已有文献十分吻合,验证了模型的正确性.     

导叶预旋角对叶轮_扩压器相干的影响

在不同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3部件之间非定常相干进行了数值模拟,并与实验结果作比较。研究了进口导叶预旋角度对叶轮及扩压器内部流动及非定常性的影响,同时探讨了3部件之间动静相干的机理。结果表明,计算结果同实验结果吻合很好。在同等流量下,进口导叶的尾流和大尺寸涡团的非定常作用使得叶轮和扩压器上的非定常性减小,其变化弧度仅在原来的1/4左右。进口导叶为负预旋时,由进口导叶尾流所带来的非定常影响比进口导叶正预旋角度下小的多,但叶轮尾流及扩压器的势反冲效应所引起的非定常效应却较正预旋角度下有所增大。     

高压比离心压气机气动设计与分析

设计了单级总压比9.5、流量1.95 kg/s的离心压气机,该压气机分为叶轮、径向扩压器和轴向扩压器三个部分。叶轮初步设计采用自编程的方法,叶型使用了双分流叶片,通过软件Numeca对叶轮进行了数值模拟,分析了入口激波和出口射流尾迹等流动结构;从性能和流场细节两方面比较了三种形式的径向扩压器。结果发现,扩压器入口收缩可以抑制回流,楔形扩压器的扩压性能明显优于无叶扩压器。     

离心压气机错排叶栅扩压器性能研究

依据叶片设计的基本理论,在原设计单列圆弧叶栅扩压器的基础上,根据相似准则设计了一种新型的双列错排叶栅扩压器;同时利用NACA叶型又设计了另一种双列错排叶栅扩压器。随后重点对三种扩压器与离心叶轮相连后的结构性能进行了详细的三维粘性数值模拟研究,并对流场中的压力、速度、极限流线和熵分布情况进行了全面的分析。研究结果表明：基于NACA叶型的双列错排叶栅扩压器可以更好地利用叶轮出口的动能,从而提高叶轮-扩压器结构的效率;但若叶栅的叶型设计不合理,则会使总压比降低,效率反而降低,即叶型对错排叶栅扩压器的性能影响较大。     

串列叶栅扩压器弦长比对离心压气机的性能影响研究

为研究串列叶栅前后排叶片的弦长比对离心压气机性能的影响规律,采用数值模拟的方法对某离心压气机扩压器进行串列改造,并在弦长比为0.7、1.0和2.0时对离心压气机级性能进行分析。研究结果表明:串列叶栅扩压器效率优于楔形扩压器,且可以明显扩宽压气机的工作裕度;串列叶栅弦长比在一定范围内数值越大,即前排叶片越短,压气机性能越佳。在串列叶栅扩压器后排叶片前缘附近添加合适弦长的小叶片可以在不降低离心压气机效率与工作裕度的同时提高总压比,同时拓宽其最大通流能力。     

叶片安装角对离心压气机扩压器气动性能及失速机理影响研究

为了研究离心压气机扩压器异常叶片对于失速现象的诱发效果,以带有叶扩压器的高速离心压气机为研究对象,通过整体或局部改变扩压器叶片安装角,开展非定常数值模拟研究并与实验结果对比验证,研究叶片安装角改变对离心压气机性能、动态特性以及失速机理的影响规律。研究表明：整体负方向旋转叶片安装角会促使扩压器更加不稳定,旋转角度从-5°到5°,最高效率点对应的质量流量逐渐增大。其中安装角偏转+5°扩压器叶片前缘靠近轮缘壁面发生流动分离,诱使无叶区间产生回流;而偏转-5°扩压器轮毂附近的流动分离主要发生在尾缘,造成扩压器叶片吸力面附近产生大范围回流。单个叶片安装角发生较大偏转(大于10°)时,扩压器比叶轮更早进入失速状态,且失速的机制可能会随着安装角偏移的增大发生改变。     

导叶叶片数对离心泵特性的影响

在比转速n_s=71的离心泵研发过程中,针对叶片数z=5的叶轮,为选择适宜叶片数的导叶,采用CFX软件对单级研发泵进行非定常数值模拟研究,分析了不同工况下导叶叶片数分别为6、7、8时泵的外特性、压力脉动和叶轮径向力,针对小流量工况径向力的较大差异,进一步对比了叶轮内流场。结果表明,减少导叶叶片数可提高较大流量工况的扬程和效率,但可能导致小流量扬程下降;小流量区间导叶叶片数对压力脉动的影响较为复杂,而较大流量工况增加导叶叶片数有益于改善压力脉动;此外,导叶叶片数越多,非额定工况的叶轮径向力越小,特别是在小流量工况,增加导叶叶片数提高了叶轮流场的均匀性,径向力缩小约4倍。最终对整体性能较优的7叶片导叶进行排产和试验,其中扬程计算误差不超过5.9%,表明数值模拟结果具有一定精度。     

自循环机匣处理对某型柴油机增压器压气机的稳定工况范围及性能影响研究

针对某型柴油机增压器压气机,基于整级全通道数值模拟和正交试验设计方法,研究了自循环机匣处理实现高亚声速压气机扩稳增效的潜力。结果表明：自循环机匣能够在提高设计点气动性能的前提下推迟失稳,但会牺牲堵塞流量。压气机的失稳和堵塞流量分别与叶片前缘及叶片扩压器中的堵塞程度相关。小流量侧自循环机匣通过抽吸叶轮叶顶附近低能流体,缓解堵塞,推迟失稳。但在大流量侧自循环机匣的喷射效应会增大扩压器进口攻角,加剧扩压器叶片流动分离,减小堵塞流量。抽吸效应与喷射效应强度均取决于抽吸槽的位置和宽度,压气机稳定性和堵塞流量与抽吸槽参数的变化基本呈负相关。自循环机匣对气动性能的影响包含两方面：在抽吸槽前,经回流槽流出的流体与主流的掺混及其产生的进口畸变将带来额外的效率和压比损失,适当减小回流槽角度可以降低该损失;在抽吸槽下游,得益于抽吸效应对叶顶流动状态的改善,压气机抽吸槽附近及下游高熵区减小,做功能力增强,气动损失大幅降低。在上述两方面共同影响下,压气机设计点气动性能最终得以提高。     

扩压器前缘开槽结构对离心鼓风机性能及流场压力脉动的影响

为提高离心鼓风机的气动性能,对一离心鼓风机扩压器叶片前缘前后盖板同时进行开槽处理,并采用数值模拟方法定量研究开槽结构对离心鼓风机气动性能及内部流场的影响。结果表明,具有开槽结构的扩压器进口回流与上游叶轮尾迹影响明显减小,其次一部分高速流体从开槽区域射入扩压器吸力面侧,并与主流掺混,从而加速了扩压器流道中后段的流动,抑制了叶片尾部的附面层分离。因此,在适宜的开槽参数下,开槽结构能提高离心鼓风机的总压升和效率。离心叶轮出口和叶片扩压器进口典型位置非定常压力脉动频域特性的结果表明:在开槽扩压器内部叶频的影响减小,而轴频起了主导作用,并发现开槽处理后,扩压器内部的压力脉动幅值明显减小,减小压力脉动的幅值在一定程度上能减弱离心鼓风机内的流动诱导噪声。     

Numerical investigation of influence of the clocking effect on the unsteady pressure fluctuations and radial forces in the centrifugal pump with vaned diffuser

The relative position between the diffuser vane and the volute tongue (clocking effect) has a great effect on the performance of the single-stage centrifugal pump, which however, is often ignored by designers. In this paper, the influence of clocking effect on the unsteady pressure fluctuation in a centrifugal pump and on the radial force of impeller is investigated. The hydrodynamic performance of the centrifugal pump with vaned diffuser was experimentally measured. Numerical simulation based on the Reynolds-averaged Navier–Stokes (RANS) combined with the SST k-w turbulence model was used to obtain hydrodynamic performance of the centrifugal pump. The numerical results of the hydrodynamic performance were in agreement with the experimental data. The results show that the clocking effect has great influence on the pressure fluctuation and on the unsteady radial force imposed on the impeller. When the diffuser vane approaches the volute tongue, the pressure fluctuation intensity in volute is relatively lower. Meanwhile, relatively larger radial force on the impeller and the lower efficiency are obtained when the diffuser vane is near the volute tongue. Thus, it is suggested that the volute tongue should be located near the middle of two diffuser vanes to obtain better performance.     

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.     

Design and optimization of a single stage centrifugal compressor for a solar dish-Brayton system

According to the requirements of a solar dish-Brayton system,a centrifugal compressor stage with a minimum total pressure ratio of 5,an adiabatic efficiency above 75% and a surge margin more than 12% needs to be designed.A single stage,which consists of impeller,radial vaned diffuser,90° crossover and two rows of axial stators,was chosen to satisfy this system.To achieve the stage performance,an impeller with a 6:1 total pressure ratio and an adiabatic efficiency of 90% was designed and its preliminary geometry came from an in-house one-dimensional program.Radial vaned diffuser was applied downstream of the impeller.Two rows of axial stators after 90° crossover were added to guide the flow into axial direction.Since jet-wake flow,shockwave and boundary layer separation coexisted in the impeller-diffuser region,optimization on the radius ratio of radial diffuser vane inlet to impeller exit,diffuser vane inlet blade angle and number of diffuser vanes was carried out at design point.Finally,an optimized centrifugal compressor stage fulfilled the high expectations and presented proper performance.Numerical simulation showed that at design point the stage adiabatic efficiency was 79.93% and the total pressure ratio was 5.6.The surge margin was 15%.The performance map including 80%,90% and 100% design speed was also presented.     

串列叶栅前后排叶片周向相对位置对离心压气机性能的影响

串列叶栅前后排叶片相对位置对串列扩压器的性能有重要影响.根据离心叶轮出口气流参数设计了一离心式串列叶栅扩压器,并利用数值模拟方法在前、后排叶栅周向相对位置分别为10%、20%、30%、40%、50%、60%、70%、80%和90%时对离心压气机级进行了计算和分析,研究周向相对位置变化对离心压气机性能的影响以及作用机理.数值模拟结果表明:随着前后排叶栅周向相对位置变化,后排叶栅前缘滞止高压区相对前排叶栅的位置发生了变化,影响了前排叶栅压力面的压力分布,从而改变了前排叶栅压力分布及大小;当前后排叶栅周向相对位置为30%时,扩压器性能达到最佳,使压气机总压比和等熵效率最大,稳定工作范围增大;前后排叶栅所形成的渐缩通道可抑制后排叶栅吸力面边界层的分离.     

两级动叶可调轴流风机内流特征的数值模拟

采用Fluent软件对某600 MW机组配套的两级动叶可调轴流一次风机进行了全三维定常数值模拟,分析了风机第一、第二级叶轮内流特征和动叶安装角对风机性能的影响.结果表明：第二级叶轮出口总压整体呈现高压区和次高压区交替分布的特征,且比第一级叶轮的对称性差;第一、第二级叶轮叶片压力面、吸力面的总压和静压分布规律相似;第二级叶轮叶片压力面和吸力面相应位置上的静压值均大于第一级叶轮叶片;随着动叶安装角的增大,第一、第二级叶轮的总压升系数和静叶的扩压系数均增大,且第二级叶轮大于第一级叶轮,表明第二级叶轮的做功能力和静叶的扩压能力均比第一级叶轮的大.     

Unstable Head-Flow Characteristic Generation Mechanism of a Low Specific Speed Mixed Flow Pump

This paper treats the flow instabilities in a mixed flow pump with a vaned diffuser. Test pump has a positive slope of a head-flow performance curve at 65% flow rate of BEP (Best Efficiency Point) because of a rotating stall. Dynamic Particle Image Velocimetry (PIV) and pressure fluctuation measurements are used for investigating the propagation mechanism of a rotating stall. It was found that unstable performance was caused by periodical large scale abrupt backflow generated from the vaned diffuser to the outlet of impeller. Further, the relation between the static pressure at the inlet of diffuser vane and the internal flow condition was clarified. From these experimental results, in order to improve the positive slope of a head-flow performance curve, to suppress the growth of strong vortex toward the inlet of diffuser vane was proved to be a key point.     

Experimental and numerical investigation on application of half vane diffusers for centrifugal pump

Vaned diffusers are widely used in centrifugal pumps, but little research has been published regarding action mechanism and the influence of diffuser vane height on dynamics performance of centrifugal pumps. Experimentally and numerically, the present investigation was focused on the dynamics performances of a low specific speed centrifugal pump equipped with vane diffusers with different vane heights. The pump performance was appraised when the diffuser vane height (h/b) was 0 (vaneless), 0.5, 0.6, 0.8 and 1 (vaned) times the diffuser width respectively. The pressure fields were numerically simulated in order to study the influence of half vane diffusers on inner flow field. The experimental results of operating performance showed that the efficiency was significantly improved for 2.5% at design flow point and the head was significantly improved for nearly 3 m at over flow point. The best efficiency point shifted towards higher flow rate with h/b reducing, and the high efficiency area was broadened by using half vane diffusers. Besides, half vane diffusers could reduce the intensity of pressure fluctuations at the leading edge of the stator vanes, and reduce the influence of rotor-stator interaction in tongue region. The numerical results showed that half vane diffusers could enhance flow uniformity in pumps, symmetry of pressure distributions on the impeller outlet and preferable regularity of radial force distributions. Therefore, it is very useful and feasible to apply half vane diffusers in centrifugal pumps.     

Effects of Diffuser Vane Geometry on Interaction Noise Generated from a Centrifugal Compressor

The characteristics of interaction tone noise radiated from a centrifugal compressor with a vaned diffuser are discussed by experiments, including visualization techniques using the oil-film method. Research attention is paid to the leading edge geometries of the diffuser vanes that are deeply related to the generation mechanism of the interaction tone noise. The compressor-radiated noise can be reduced by several decibels by setting some clearances in both the hub and shroud surfaces of the diffuser wall along with some decline in the pressure-rise coefficient. Since the decline turned out to be caused by the flow impingement and also by the secondary flow within the diffuser passages, several new types of diffuser vane geometries which do not detract from both the performance and noise level are developed and utilized for the experiments. The presented diffuser vane geometries will offer a few basic guidelines for the diffuser vane design.     

Unsteady behavior and control of vortices in centrifugal compressor

Two examples of the use of vortex control to reduce noise and enhance the stable operating range of a centrifugal compressor are presented in this paper.In the case of high-flow operation of a centrifugal compressor with a vaned diffuser,a discrete frequency noise induced by interaction between the impeller-discharge flow and the diffuser vane,which appears most notably in the power spectra of the radiated noise,can be reduced using a tapered diffuser vane（TDV） without affecting the performance of the compressor.Twin longitudinal vortices produced by leakage flow passing through the tapered portion of the diffuser vane induce secondary flow in the direction of the blade surface and prevent flow separation from the leading edge of the diffuser.The use of a TDV can effectively reduce both the discrete frequency noise generated by the interaction between the impeller-discharge flow and the diffuser surface and the broadband turbulent noise component.In the case of low-flow operation,a leading-edge vortex（LEV） that forms on the shroud side of the suction surface near the leading edge of the diffuser increases significantly in size and blocks flow in the diffuser passage.The formation of an LEV may adversely affect the performance of the compressor and may cause the diffuser to stall.Using a one-side tapered diffuser vane to suppress the evolution of an LEV,the stable operating range of the compressor can be increased by more than 12 percent,and the pressure-rise characteristics of the compressor can be improved.The results of a supplementary examination of the structure and unsteady behavior of LEVs,conducted by means of detailed numerical simulations,are also presented.