叶尖间隙对轴流压气机近失速叶尖流动的影响

为研究动叶间隙大小对轴流压气机近失速叶尖流动的影响,以一台高亚声速一级半压气机级为研究对象,在设计间隙、小间隙及2个大间隙下进行定常三维数值模拟。计算结果表明,设计间隙下压气机喘振裕度最大,随着间隙增大,裕度近似呈线性降低,失速形式由动叶吸力面分离引起的"叶尖失速"转变为"泄漏涡堵塞失速"。大间隙情况下,叶尖前缘附近发出的泄漏流形成松散的涡系结构,诱导中部及尾缘附近泄漏流共同形成回流及大量二次泄漏,堵塞转子通道进口,引起失速的发生。     

跨音速压气机转子叶尖间隙流场特性研究

为了分析跨音速转子叶尖间隙高度对转子叶尖流场的影响,以某轴流压气机跨音级为研究对象,采用全三维数值模拟方法,探讨了设计点和近失速工况下叶尖泄漏涡与激波的相互作用现象及不同的间隙条件下叶尖泄漏涡的演化、发展规律.计算结果表明,与设计点相比,近失速工况下间隙泄漏涡在流场中的位置及其与叶片弦长的夹角基本不变,但其对激波的影响...     

核心机驱动风扇级转子叶尖流动结构和机理的研究

为了探究核心机驱动风扇级不同工作模式下转子叶尖流动结构和机理,对某核心机驱动风扇级转子流场进行了三维定常数值模拟,分析了单外涵模式和双外涵模式下工作点及近失速点转子叶尖流场结构特点,并研究了不同叶尖间隙对核心机驱动风扇级性能的影响。结果表明:单外涵模式与双外涵模式设计点叶尖泄漏涡起始位置不同;单外涵模式转子叶尖存在贯穿流道的正激波,双外涵模式该正激波消失;泄漏涡经过转子叶尖超声速区域会形成低速带;单外涵模式时泄漏涡经过正激波后发生扩散,并使正激波出现"缺口";转子叶尖间隙大小对核心机驱动风扇级两种工作模式下的流量、压比和等熵效率影响均较小,间隙增大到一定程度后稳定裕度下降剧烈。     

周向布局对串列转子气动性能的影响研究

串列叶栅是提高轴流压气机气动负荷的有效途径。在串列转子设计中,前后排转子的周向相对位置对其效率和失速裕度具有重要影响。研究发现当后排转子前缘靠近前排转子压力面时,串列转子效率和失速裕度均要优于其他周向布局形式。在设计工况,后排转子的势影响对前排转子吸力面流动有着重要影响,当后排转子前缘逐步靠近前排转子压力面时,可以改善前排转子吸力面尾缘区域的压力梯度,避免吸力面发生流动分离;在近失速工况,当后排转子前缘靠近前排转子压力面时,利用后排叶尖泄漏流与前排尾迹之间的流动掺混,可以有效减小后排通道中叶尖的气动堵塞,有效拓宽串列转子的失速裕度。     

进口总压畸变条件下离心压气机流动失稳特性的数值研究

采用数值模拟方法对比分析了畸变进口与均匀进口条件下离心压气机的气动性能。结果发现，离心压气机展现出一定的抗畸变能力，总压畸变对压气机整体性能未造成显著影响。进一步的分析表明，在均匀来流条件下，随着流量的降低，主叶片和分流叶片之间的低速区逐渐向叶顶区域发展，阻碍主流流动，相互排挤并由叶顶间隙溢出；畸变来流条件下，在近失速工况点时，叶顶沿流向流动出现局部负速度，叶顶泄漏涡前移，在进口畸变产生的低压区内吸力面流动分离增大，进而演变出龙卷风涡阻塞流道，并影响到相邻叶片，引发前缘溢流；通过Q-准则方法发现，在畸变来流条件下，近失速工况下的涡结构分为前缘失速涡、叶顶间隙泄漏涡、通道涡和前缘溢出涡。     

进口总压畸变对压气机性能及流场影响的机理研究

采用全三维非定常数值方法研究进口周向总压畸变对轴流压气机转子性能及内部流场的影响,数值结果表明进口周向总压畸变后不仅降低压气机的稳定裕度,也使压气机等熵效率减少。通过详细地分析压气机内部流场,揭示了进口周向总压畸变对该压气机转子性能及流场影响的机理,即进口周向总压畸变后,明显降低50%～100%叶展内的气流进气角。同时增强产生叶尖泄漏运动的驱动力,提前使叶顶间隙泄漏涡涡核破碎,造成高的堵塞,最终触发压气机失速。     

自循环机匣处理喷气位置对压气机性能的影响

为了揭示自循环机匣处理对Stage 37气动性能的影响机理，利用数值模拟方法研究了不同喷气位置对压气机气动性能的影响。在设计转速时，分析了不同喷气位置的自循环机匣处理装置的叶尖流场，探讨了自循环机匣处理的扩稳机理。数值模拟结果显示：不同喷气位置的自循环机匣处理在略微降低压气机效率的情况下，能够分别扩大2.96%，2.72%，2.83%，2.6%的失速裕度；设计转速时，Stage 37中转子叶尖区激波/叶尖泄漏涡相互干涉以及泄漏涡破裂后产生的阻塞区，是影响Stage 37压气机内部流动失稳的关键因素。自循环机匣处理的扩稳机制主要在于利用高速喷气抑制叶尖泄漏涡的破碎程度，减小叶尖阻塞区面积，进而提高压气机的失速裕度。     

背掠式离心转子设计中叶片涡分布对其性能影响的研究

基于“全可控涡”的思想,对小型高转速离心式压气机s2流面通流的气动设计计算方法进行了较深入的研究与分析,通过背掠式转子算例,将验算结果同原始数据作对比分析,验证了该方法的有效性;在此基础上,通过给定不同的叶片涡分布,计算分析了叶片涡对叶片相对速度的影响,以及对背掠式转子性能的影响,为通过叶片涡分布来比较好地控制叶片通道内子午面速度分布提供了一种有效的技术途径,可为进一步设计高性能背掠式转子提供参考依据。     

跨音速涡轮定常与非定常叶尖泄漏流机理分析

针对格拉兹大学单级跨音涡轮流场进行数值模拟并分析其叶尖泄漏涡结构与非定常影响机理.结果表明:泄漏涡于破碎前为类Rankine涡结构,破碎后卷吸入间隙流体,同时受涡核卷吸而围绕其运动的部分间隙流与主流掺混,形成高剪切流区域,形成类Sullivan涡结构的亚临界状态.非定常尾迹含有的流向涡量与叶尖泄漏涡-刮削涡涡对相互作用...     

基于谐波平衡法的跨声速风扇颤振特性数值模拟

由于叶片振动诱发的非定常响应具有时间周期性的特点,采用频域谐波平衡计算技术,结合结构动力学分析方法,基于流固单向耦合的方式数值模拟了振荡叶片下的非定常流场,通过评估结构和流体之间的能量传递关系对叶片的颤振特性进行了预测。针对某两级风扇的第一级转子叶片,通过给定不同的转速和出口背压条件对比研究了叶片的气动弹性稳定性,并给出了叶片的颤振失稳边界,计算结果显示:在100%、95%、90%转速下的非失速工况中叶片存在失稳风险,意味着发生颤振的类型为超音速非失速颤振;不同工况下,激波下游和叶顶前缘附近气流做功的综和效应决定了叶片的气动弹性稳定性。     

COMPUTATIONAL AND EXPERI- MENTAL STUDY ON TIP LEAKAGE VORTEX OF CIRCUMFERENTIAL SKEWED BLADES

In the steady operation condition,the experiments and the numerical simulations are used to investigate the tip leakage flow fields in three low pressure axial flow fans with three kinds of circumferential skewed rotors,including the radial rotor,the forward-skewed rotor and the back-ward-skewed rotor. The three-dimensional viscous flow fields of the fans are computed. In the ex-periments,the two-dimensional plane particle image velocimetry (PIV) system is used to measure the flow fields in the tip region of three different pitchwise positions of each fan. The results show that the computational results agree well with the experimental data in the flow field of the tip region of each fan. The tip leakage vortex core segments based on method of the eigenmode analysis can dis-play clearly some characteristics of the tip leakage vortex,such as the origination position of tip leak-age vortex,the development of vortex strength,and so on. Compared with the radial rotor,the other two skewed rotors can increase the stability of the tip leakage vortex and the increment in the for-ward-skewed rotor is more than that in the backward-skewed one. Among the tip leakage vortices of the three rotors,the velocity of the vortex in the forward-skewed rotor is the highest in the circumfer-ential direction and the lowest in the axial direction.     

低压轴流风机叶顶间隙对叶尖涡及外部性能的影响研究

基于其一动叶可调的低压轴流风机叶轮,通过对其在不同叶顶间隙下的叶顶区域进行数值模拟分析。计算结果分析表明:该轴流风机在叶顶间隙较小时虽然会出现泄漏流动,但不一定会出现泄漏涡,随着叶顶间隙的增大,泄漏流动将变得不明显,取而代之的是泄漏涡,并且泄漏涡的强度和影响区域随着间隙的增大而增大;在相同流量下,通风机的全压随着叶顶间隙的增大而减小;随着流量的降低,叶顶间隙越大,越早进入非稳定状态。     

叶顶间隙对低比转速混流泵性能及内部流场影响的数值研究

为了解叶顶间隙对低比转速混流泵性能及内部流场的影响,选取无叶顶间隙和叶顶间隙δ分别为0.25 mm、0.75 mm和1 mm共四种方案,基于ANSYS-CFX对一比转速为149的混流泵进行了全流道数值模拟。计算域采用ICEM-CFD和TurboGrid进行结构化网格划分。利用Tecplot对计算结果进行处理,得到叶顶间隙对外特性参数、轮缘泄漏、流道中心S2流面流场等的影响。结果显示,叶顶间隙对大流量工况（1.25Q_d和1.5Q_d）下性能参数的影响大于小流量工况（0.5Q_d和0.75Q_d）,且效率减小量与叶顶间隙变化量的比值（Δη/Δδ）和相对流量m之间近似呈二次抛物线关系;当间隙为0.75 mm时,随着流量的增加,在叶轮流道进口附近形成的旋涡逐渐向出口方向移动,且旋涡强度及其对主流的影响范围均增大;当间隙进一步增大到1 mm时,泄漏流和主流之间发生了更为严重的卷吸效应。     

EXPERIMENTAL INVESTIGATION OF TIP CLEARANCE FLOW FOR AN AXIAL FLOW FAN ROTOR

The flow field in the tip region of an axial ventilation fan is investigated with a particle image velocimeter (PIV) system at the design condition. Flow fields with three different tip clearances are surveyed on three different circumferential planes, respectively. The phase-locked average method is used to investigate the generation and the development of a tip leakage vortex. The result from PIV system is compared with that from a particle dynamics anemometer(PDA) system. Both data are in good agreement and the structure of the tip leakage vortex for the rotor is illustrated. The characteristic of a leakage vortex is described in both velocity vectors and vortical contours. The unsteadiness of the leakage vortex and the position of the vortex are surveyed in detail, which interprets the discrepancy between the numerical simulation and PDA experimental results to a certain extent. The center loci of tip leakage vortex at different times and the mean center loci of the leakage vortex are displayed particularly. Finally, the trajectories of the tip leakage vortex by the experimental measurement are compared with predictions from the existing models for high speed and high-pressure compressors and turbines when appropriately interpreted. A good agreement is obtained.     

Study on unsteady tip leakage vortex cavitation in an axial-flow pump using an improved filter-based model

The aim of the present investigation is to simulate and analyze the tip leakage flow structure and instantaneous evolution of tip vortex cavitation in a scaled axial-flow pump model. The improved filter-based turbulence model based on the density correction and a homogeneous cavitation model were used for implementing this work. The results show that when entering into the tip clearance, the backward flow separates from the blade tip near the pressure side, resulting in the generation of a corner vortex with high magnitude of turbulence kinetic energy. Then, at the exit of the tip clearance, the leakage jets would re-attach on the blade tip wall. Moreover, the maximum swirling strength method was employed in identifying the TLV core and a counter-rotating induced vortex near the end-wall successfully. The three-dimensional cavitation patterns and in-plain cavitation structures obtained by the improved numerical method agree well with the experimental results. At the sheet cavitation trailing edge in the tip region, the perpendicular cavitation cloud induced by TLV sheds and migrates toward the pressure side of the neighboring blade. During its migration, it breaks down abruptly and generates a large number of small-scale cavities, leading to severe degradation of the pump performance, which is similar with the phenomenon observed by Tan et al. [35].     

Numerical study on near-stall flow unsteadiness in an axial compressor with casing treatment

Time-accurate numerical calculations were performed to investigate unsteady flow features in a low-speed axial compressor. The test compressor has axial skewed slots over the rotor tip region as casing treatment to improve the stall margin. The calculated data are in good agreement with the measured data. This paper reports the effect of casing treatment and flow unsteadiness on the rotor near stall by examining the flows in the smooth wall and casing treatment cases. The axial skewed slot can remove the blockage induced by the tip clearance leakage flow by removing and injecting the flow near the tip. However, for the casing treatment case, blockage is induced near the hub because the hub-corner stall is caused by a decrease in the axial momentum in this region. The tip leakage flow has inherent unsteadiness in the smooth wall case caused by the relatively large tip clearance, whereas the hub-corner stall has unsteadiness in the casing treatment case. The two types of unsteadiness have functions in inducing stall inception. Furthermore, axial slots of different sizes were tested to examine the effect of slot geometry on rotor flow stability. The change in flow structure related to the stall inception was subject to flow injection through the recirculation in the slots.     

对旋轴流风机叶顶间隙对其性能的影响

为了探究改变对旋轴流风机两级叶轮的叶顶间隙对其性能的影响，建立不同叶顶间隙下风机三维模型，利用Fluent进行数值模拟，并结合风机性能试验验证仿真的正确性。分析压升、效率、轴功率、湍流动能和叶顶泄漏涡随两级叶轮叶顶间隙的变化情况，结果表明：在相同流量下，压升、效率随间隙的增大而减小；与第一级叶轮相比，间隙对第二级叶轮的轴功率、湍流动能及泄漏涡影响更加显著；随间隙增大，叶顶泄漏涡的强度和影响区域越大。     

Numerical study on unsteadiness of tip clearance flow and performance prediction of axial compressor

Numerical calculations were performed to investigate unsteady features of tip clearance leakage flow in an axial compressor. The first stage rotor of a low speed axial compressor with a large tip clearance was examined. It was confirmed that the numerically calculated performance data were in good agreement with the experimentally measured performance data. Using frequency analysis, the flow characteristic near the casing induced by tip clearance leakage flow was found to be not associated with the rotating speed of the rotor. This characteristic is called rotating instability or self-induced unsteadiness. We found that the circumferential length scale of the rotating instability of the compressor was longer than a pitch of a blade passage; therefore, a multi-blade passage was adopted to study the flow structure more precisely. The flow characteristic was described by the frequency, the circumferential length, and the phase velocity, and was changed by operating points toward stall. The behavior of the flow was characterized by circumferentially traveling waves. Hence, the mechanism governing the development of the unsteady feature was further examined in terms of the rotating wave pattern of the pressure distribution. Furthermore, the unsteady feature of the tip clearance leakage flow affected the prediction of compressor performance by altering blockage, flow turning, and loss near the casing.     

考虑间隙的压气机转子内部流动的数值模拟

采用时间推进法求解三维N-S方程，开发了一种用于计算考虑顶部间隙的压气机转子内部流场的三维粘性程序。对某压气机转子顶部间隙内的流动进行了详细的数值模拟，计算结果与试验结果吻合良好。通过分析可以发现，动叶顶部问隙的流动将引起叶片顶部气流的欠偏转，从而降低了转子附近相当大区域内的做功能力。同时，对于间隙内细微的流动结构也进行了较为深入的分析。     

蜂窝密封流场和泄漏特性的实验研究

利用烟线法,显示了蜂窝腔中空气的流动情况,揭示了蜂窝腔中旋涡的结构特点。表明在相同的入口条件下,间隙越小,进入蜂窝腔的气流与水平面的夹角越大,且旋涡体积越大、中心位置越靠近底面。同时,在不改变实验其它参数的情况下,改变蜂窝的深度,通过实验观察蜂窝密封的泄漏量。结果表明,在不同的入口压力情况下,蜂窝深度与蜂窝对边距的比值为0.52左右时,蜂窝密封的泄漏流量最小。