轴流压气机叶顶喷气扩稳机理试验研究

轴流压气机叶顶喷气已经被证实能够有效拓宽压气机的失稳裕度。在一台低速单转子轴流压气机上进行叶顶喷气试验研究,采用喷气动量比作为衡量失速裕度改善的指标,并通过改变叶顶间隙和喷气角度对不同喷气量的扩稳效果进行分析,试验中发现随着叶顶喷气动量比的增加,压气机失速裕度的变化会出现两个拐点,即存在两个喷气动量比分界点,并将喷气动量比分界点前后的三个阶段对应的喷气量分别定义为微喷气,大喷气和超大喷气。通过试验测量压气机进出口气动参数以及壁面动态压力信号对喷气动量比分界点前后叶顶喷气扩稳机理进行详细的分析。试验分析结果表明:微喷气扩稳仅仅是因其能够减弱叶顶间隙泄漏涡和叶顶间隙泄漏流非定常性;大喷气则能够同时减小进口气流攻角,推迟叶片吸力面分离和抑制叶顶间隙泄漏涡,推迟叶顶间隙泄漏流非定常性的产生;超大喷气虽能够推迟叶顶间隙泄漏流非定常性的产生,但喷气的影响区域已严重向叶片通道内部转移,甚至影响了压气机的做功能力。     

跨音轴流压气机自循环喷气扩稳试验研究

轴流风扇/压气机稳定性控制一直叶轮机械领域迫切需要解决的难题,特别是对于内部流动复杂的跨音转子。提出以自循环喷气方式作为控制手段,并在一台单级跨音风扇/压气机上进行试验研究。试验中通过自行设计自循环机构在压气机上进行基于自循环的叶顶喷气研究,并考察不同抽气角度和喷气偏航角对压气机稳定裕度和效率的影响,并通过测量机匣壁面非定常压力信号对跨音压气机自循环喷气机构中前端喷气的扩稳机理进行分析。试验结果表明:自循环喷气能够有效拓宽跨音压气机的流动失稳裕度,并取得了8%~15%的扩稳效果,而且能够略微提高压气机峰值点的效率。另外,通过功率谱密度分析,前端叶顶喷气的扩稳机理仍然是影响叶顶间隙泄漏流的非定常性。     

周向槽机匣处理的数值研究及扩稳机理分析

结合周向槽机匣处理试验结果,采用全三维的数值方法对带周向槽机匣处理的亚音速轴流压气机内部流动进行研究。试验与数值结果均表明周向槽机匣处理能扩大压气机的稳定工作范围,同时略微地降低压气机效率。在两个转速下,数值模拟结果与试验结果符合良好。通过详细地分析压气机叶顶流场表明实体壁机匣时,触发该压气机失速的主要原因是间隙泄漏涡涡核破碎,使得叶顶通道堵塞程度严重。采取周向槽机匣处理能降低产生叶尖泄漏运动的驱动力,有效地削弱了间隙泄漏流造成的负面影响。与此同时,周向槽具有抽吸或吹除机匣端壁区低相对总压流体的能力,使低能气团在叶顶通道堆积的范围大为缩小,提高了叶顶通道内的流通能力。     

组合型周向槽机匣处理优化方案的数值研究

为研究压气机子午面不同深度组合型周向槽机匣处理的扩稳效果,针对跨声速rotor37转子叶栅机匣设计了4种不同深度组合的周向处理槽。数值模拟研究结果表明,在设计转速下,带周向槽机匣处理的转子综合稳定裕度有不同程度的提高,优化方案综合稳定裕度由9.65%提高到了16.42%,而效率只下降了0.87%。此外,在叶顶弦长中后部采用浅槽可进一步提升扩稳效果。     

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,但其对激波的影响更大。此外,随着叶尖间隙的增大,叶尖泄漏涡的强度、尺寸和影响范围也会逐渐增加,降低叶片的扩压能力。     

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。     

叶顶喷气对跨音速轴流压气机稳定裕度影响的数值研究

为了研究叶顶喷气机匣处理方式对轴流压气机稳定裕度的影响，针对Rotor37开展了叶顶喷气的定常数值研究。相关文献指出，喷嘴出口气流角、喷嘴轴向位置、喷嘴覆盖比率及喷嘴进口总压4个参数对稳定裕度的影响最为显著。因此，本文着重对这四个参数构建响应面，同时结合主流的单通道计算模型，详细分析了它们之间的交互关系及相应的参数变化对压气机稳定性的影响，并拟合出回归方程。结果显示，在最佳参数设置下，单通道计算模型中压气机的稳定裕度最大可以增加8%左右。在此基础上，又对四通道压气机计算模型进行了气动计算与分析，发现叶顶喷气射流会按照与压气机旋转相反的方向作用于相邻的叶片流道，抑制该流道泄漏涡的产生，进而改善该流道内的流动。研究表明，采用叶顶喷气方法可以降低叶片前缘载荷，改变压气机的失速类型，从而增加压气机的稳定裕度。     

自循环机匣对高速离心叶轮性能及稳定性影响的研究

本文以某高速离心压气机为研究对象,通过数值模拟的方法,研究了叶轮失稳流场和两种自循环机匣对其性能的影响,以期揭示自循环机匣影响叶轮性能和内部流场的内在机理。研究首先模拟叶轮在实壁机匣下的情景,发现小流量工况下的叶片表面二次流强度明显增大,在叶轮前缘和叶顶泄漏流大量掺混,以至于在分流叶片通道进口出现了大范围堵塞,形成大范围"尾迹区",引起叶片失速。针对上述现象,研究模拟叶轮在两种不同后槽位置的自循环机匣下的情景。采用自循环机匣结构后,最高能使失速裕度提升6%,设计点效率下降0.5%。在小流量工况下,气流主要由主叶片压力面附近流入机匣结构中。有效降低了叶顶泄漏流强度和压力面叶顶通道涡强度,同时还增加叶轮进口的流量,减小叶轮进口的气流攻角,降低了流动损失。     

串列叶栅和叶片弯曲对角区失速和叶尖泄漏流的耦合作用

为了提高压气机叶栅的气动性能,本文针对高负荷串列叶栅进行数值模拟,研究了叶片正弯和串列叶栅对角区失速和叶尖泄漏流的耦合作用。结果表明,在串列叶栅前叶排存在比较严重的角区失速,叶片正弯能有效控制高负荷串列叶栅中的角区失速,在最优工况叶栅总损失降低了37.6%。串列叶栅中只有"前排叶片弯曲"的方案能取得与"两排叶片都弯曲"方案相似的控制效果,但由于"两排叶片都弯曲"方案对两排叶片都有控制作用,从而获得了更低的总压损失。叶尖泄漏流可以有效控制上端壁处的角区失速,同时也会带来泄漏流损失。叶尖间隙越大,叶栅的总压损失越小,叶栅中涡结构也会越复杂。大间隙下,叶尖泄漏涡和通道涡的位置与一般压气机叶栅不同,两排叶片各自生成的泄漏涡会在叶栅后汇聚成一个涡,通道涡由叶栅中的低能流体与一部分泄漏流组成。弯曲叶片主要作用是控制角区失速,对叶尖泄漏流的影响不明显。     

离心压气机机匣处理多工况性能预测与分析

机匣处理作为一种高效、经济的扩稳技术,越来越多的被用以提高压气机的稳定工作裕度。为了研究机匣处理对离心压气机多工况性能的影响,本文对3种进气回流机匣结构的压气机模型和无机匣处理的实壁压气机模型分别进行了数值仿真分析。数值计算结果与最优模型的试验结果吻合较好,比较准确的预测了喘振边界的位置,验证了计算方法的可靠性。结果表明,只有结构合理的进气回流机匣处理才能在各个转速下均显著扩大压气机小流量的稳定工作范围,其中机匣处理的开槽位置和前置导流挡板对其性能有着重要影响。     

压气机叶顶微喷气扩稳研究（英文）

The mechanism of compressor stall margin enhancement using the tip air injection is explored. The transonic compressor, NASA Rotor 37, is taken as the object to study the tip clearance flow under active control of tip air injection by numerical simulations. The effects of injection parameters(injection total temperature, injection position, injection angle, injection mass flow, injection port size, injection type and etc) on the stall margin extension are emphatically analyzed. Results show that the enhancement of tip leakage vortex enlarges the low-energy region induced by the shock wave in the row channel when the working condition is moving to stall point. In addition, the enhancement of radial vortex increases its entrainment ability, which tends to expand separation zone. Once the tip injection imposed, the decrease of the leakage vortex intensity widens the stall margin, while the total pressure loss increases to some extent due to the mixing of the tip micro jet with the mainstream. It is found that injection parameters should be restricted to a moderate region so as to achieve a good stall margin extension without an excessive increase in the pressure loss.     

叶尖密封流场的细观特性对叶轮机械性能的影响

细观尺度是微观与宏观之间的中间层次。利用细观力学的思想，分析了叶尖密封流场的细观特性对叶轮机械性能的影响，认为旋涡等流体的细观结构，在叶尖密封流场中起着关键性作用。密封间隙区域的细观特性即泄漏涡、激波和二次流之间的相立作用等，形成了阻塞区域，不仅影响泄漏量，还影响转子的稳定性。叶尖泄漏涡是叶尖间隙气流流动阻塞和引起压气机转子尖部紊流脉动的主要因素。     

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.     

Injection profile effects on low speed axial compressor stability enhancement

This study presents stability enhancement of a four-stage low speed axial compressor with different injection profiles. The injection profiles include one-step injection, multi-step injection, and continuous injection. For the tip injection, eight Coanda-shaped nozzles have been installed at eight equally spaced circumferential locations upstream of the first stage rotor. Two external blowers injected air steadily through the Coanda-shaped nozzles. With tip injection, the compressor operation range has been extended. To analyze stall margin improvement, spatial Fourier transform (SFT) has been performed. The coefficient of SFT (SFC) is a complex number, containing information about the magnitude and the phase of SFC. By analyzing the distribution of the magnitude and the phase of SFC, the stall onset point has been verified. Furthermore, the injection flow rate has been changed during injection process to examine the possibility of attaining an additional flow extension. Increasing the injection rate during stabilization can bring about additional operation range extension. These results suggest a new injection method to reduce the total amount of the injection air.     

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.     

轴流压缩机转子叶顶扩稳结构设计

为控制泄漏流提高压缩机的稳定工作裕度,采用了叶顶前缘端削与叶顶篦齿组合的设计。对该结构的数值研究表明:前缘端削通过引入高能来流对间隙泄漏流的抑制作用增强,篦齿在一定程度上阻断泄漏流由压力面向吸力面的流动,二者共同作用使压缩机在不同转速下的稳定工作裕度均获得一定提升。     

Inlet Recirculation Influence to the Flow Structure of Centrifugal Impeller

Inlet recirculation is proved as an effective way for centrifugal compressor surge margin extension,and is successively used in some engineering applications.Unfortunately its working mechanism is still not being well understood,which leads to redesigning of inlet recirculation mostly by experience.Also,most study about inlet recirculation is steady to date.It is necessary to study surge margin extension mechanism about inlet recirculation.To expose the mechanism in detail,steady and unsteady numerical simulations were performed on a centrifugal compressor with and without inlet recirculation.The results showed that,with inlet recirculation,the inlet axial velocity is augmented,relative Mach number around blade tip leading edge area is significantly reduced and so is the flow angle.As the flow angle decreased,the incidence angle reduced which greatly improves the flow field inside the impeller.Moreover,inlet recirculation changes the blade loading around blade tip and restrains the flow separation on the blade suction side at the leading edge area.The unsteady results of static pressure around blade surface,entropy at inlet crossflow section and vorticity distributions at near tip span surface indicated that,at near stall condition,strong fluctuation exists in the vicinity of tip area due to the interaction between tip leakage flow and core flow.By inlet recirculation these strong flow fluctuations are eliminated so the flow stability is greatly enhanced.All these improvements mentioned above are the reason for inlet recirculation delays compressor stall.This research reveals the surge margin extension reason of inlet recirculation from an unsteady flow viewpoint and provides important reference for inlet recirculation structure design.     

Stall inception and warning in a single-stage transonic axial compressor with axial skewed slot casing treatment

Characteristic changes in the stall inception in a single-stage transonic axial compressor with an axial skewed slot casing treatment were investigated experimentally. A rotating stall occurred intermittently in a compressor with an axial skewed slot, whereas spike-type rotating stalls occurred in the case of smooth casing. The axial skewed slot suppressed stall cell growth and increased the operating range. A mild surge, the frequency of which is the Helmholtz frequency of the compressor system, occurred with the rotating stall. The irregularity in the pressure signals at the slot bottom increased decreasing flow rate. An autocorrelation-based stall warning method was applied to the measured pressure signals. Results estimate and warn against the stall margin in a compressor with an axial skewed slot.     

离心压缩机喘振特性及喷射扩稳研究

以某单级离心压缩机为研究对象,搭建工况动态特性实时监测系统,通过控制排气调节阀的开度展开喘振实验研究,在此基础上,设计和实现离心压缩机的主动控制喷射扩稳,通过小孔喷射高速气流实现喘振裕度的提升。研究表明:出口压力脉动幅度大大高于进口压力脉动,进气管道流动进入深度喘振的起始时刻要落后于排气管道进入深度喘振的起始时刻;机匣喷射在增大喘振裕度的同时提高了排气压力,增大的气流喷射量使扩稳效果更加显著;机匣喷射改善了叶顶区域的流动状况。     

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.