【作者】 陆华伟；

【导师】 王仲奇； 陈浮；

【作者基本信息】 哈尔滨工业大学 ， 动力机械及工程， 2008， 博士

【摘要】 现代航空工业的快速发展,要求不断提高航空发动机的性能。而压气机作为航空涡轮发动机三大核心部件之一,其气动性能的改善对整个航空发动机的性能提高起着至关重要的作用。更高的效率及压比、更大的负荷与喘振裕度、更小的尺寸及更轻的重量成为压气机性能提高的目标所在。基于这一背景,本文通过对一台重复级低速轴流压气机流场的详细测量,分别研究了采用直静叶及正弯静叶的压气机在不同轴向间隙、不同流量工况及不同静叶时序位置下的流动特性,并通过数值模拟的手段对流场进行了验证,补充了实验过程中无法测得的流场细节。最后以此为基础,通过拓扑分析的方法,给出了带叶根间隙的压气机静叶流道内的详细涡系结构,并指出了设计工况下流场的拓扑规律和不同静叶之间的流场差异。根据实验结果,在原型轴向间隙方案下,采用直、弯静叶的压气机中都存在明显的时序效应,且时序效应随着流量的增加而增强。通过考察两列静叶时均尾迹相对位置与效率之间的联系,验证了经典的尾迹/前缘干涉理论:当前级叶列时均尾迹扫在后级同名叶列前缘附近时,对应效率最高的时序位置;当前级叶列时均尾迹位于后级同名叶列流道中央时,对应效率最低的时序位置。相比较而言,采用正弯静叶时由于尾迹形状复杂易于掺混耗散,因此压气机时序效应要弱于采用直静叶时,但前者效率明显高于后者。由于在原型间隙方案下采用正弯静叶的压气机扩压能力略弱于采用直静叶时,因此其效率提高的主要原因在于输入扭矩的减小。实验结果还表明,正弯静叶对吸力面角区低能流体的径向迁移作用减小了两端的流动损失,而正弯静叶在近喘工况下对流场的较强控制作用也是喘振裕度提高的原因所在。当同级动、静叶间轴向间隙减小后,一级静叶和二级动叶间距离拉长,一级静叶尾迹在进入二级动叶之前耗散加剧,无法在二级静叶流道内形成清晰的干涉作用,时序效应因此而减弱。随着轴向间隙的减小,压气机扩压能力得到提高,扭矩也随之上升,这使得效率先增后减,说明存在一个最佳轴向位置使得压气机整机效率达到最优。此外,静叶对气流的折转能力也随着轴向间隙的减小而增大,但通流能力有所减弱。轴向间隙减小后,采用正弯静叶的压气机压比提升的幅度要高于采用直静叶的压气机,但扭矩增长却低于后者,因此,在小轴向间隙下采用正弯静叶的压气机比采用直静叶时获得了更显著的效率提升。在近喘工况下,采用直静叶的压气机出口流场随着轴向间隙的减小而急剧恶化,而采用正弯静叶时则没有明显变化,说明正弯静叶对流场的强力控制作用在小轴向间隙下能体现出更大的优势。设计工况下,采用正弯静叶压气机的最佳轴向间隙要小于采用直静叶时,这表明采用正弯静叶的压气机能在更小的轴向间隙下获得更高的效率提升,而更小的轴向间隙同时还能带来减轻发动机重量的效果。针对实验结果数据量少、流场细节显示不够清晰的缺陷,选用了商业软件CFX11.0对流场进行了详细的数值模拟,对计算结果的精度校核显示,数值模拟的结果可以作为流场定性分析的依据。通过对数值模拟结果的拓扑分析,发现具有叶根间隙的压气机直静叶流道前后主要存在三个大尺度旋涡,分别是流道顶部的上通道涡、流道底部的刮削涡和尾缘后形成的集中脱落涡。此外还存在着若干个小尺度的旋涡结构:如马蹄涡压力面分支、壁角涡压力面分支及叶片出口吸力面叶顶附近的回流形成的旋涡以及叶根间隙内的一系列旋涡结构。相比之下,正弯静叶流道内的旋涡结构则相对较为简单,其中包括与直静叶流道中相同的上通道涡、刮削涡、一个集中脱落涡及马蹄涡压力面分支和壁角涡压力面分支,但其生成位置和旋涡尺度有所区别;另外正弯静叶流道后多衍生出一个集中脱落涡,但在叶根间隙中的旋涡结构由于增强的泄露流动而全部消失不见。当沿流向的压力梯度性质发生变化时(顺压梯度和逆压梯度之间的相互转化),流场内的奇点总数增加,流动混乱程度加剧,而当气流逐渐“适应”该压力梯度后,流场结构开始简化,若没有再次发生压力梯度的变化,则流场内的总奇点数将会维持在一个相对稳定的数量上。比较直、弯静叶流道内的拓扑结构,后者在流道内的总奇点数明显少于前者,主要原因在于正弯静叶的流动控制能力减少了叶片表面的半奇点数,而叶根间隙内的泄漏也对总奇点数造成了一定的影响;另外,在流道出口后,由于正弯静叶的表面径向分力对流场残留的扰动作用和尾迹的掺混加剧,导致了最终的稳定流场要比直静叶中更复杂一些。更多还原

【Abstract】 The performance of aero-engine needs to be improved while the aviation industry develops rapidly in the modern time. The compressor, As one of the three key parts of turbine engine, its aerodynamic performance improvement is very important for aero-engine’s development. The higher efficiency and total pressure ratio, the more load and surge margin, and the less size and weight becomes the aim of performance improvement of compressoe.For this purpose, a detailed experimental investigation has been carried out in a low speed double stage compressor with straight stator and positive bowed stator in different axial gaps at different work condition. Then, Numerical simulation is done to verify the flow field and makeup more details which can not be measured in experiment. At last, based on the calculation results, the thesis gives out the detail vortex structure in compressor stator passage with hub tip proceeding from topological analysis method. It also gives out the topological law for flow field at design condition and between different work conditions.Based on the results of experiment, the clocking effect exists clearly in compressor both with straight stator and bowed stator in original axial gap and strengthens while the massflow increases. The relation between efficiency variationg and relative wake position of two stator rows is studied to validate the classical theory of wake interference. The maximum efficiency is obtained when the upstream stator wake mixes with the downstream stator’s wake and the minimum efficiency occurs when the upstream stator wake locates in the middle of the downstream stator’s passage. Comparing with straight stator and bowed stator, the wake of bowed stator dissipates more easily because of its complex shape, and its clocking effect is weaker than straight stator. In the original axial gap scheme, the diffusion capability of compressor with positive bowed stator is weaker than the one with straight stator. But its input tonque is less than the latter’s. These two factors make the efficiency of compressor with positive bowed stator is higher than the compressor with straight stator. The result of experiment also shows than the spanwise transition effect of positive bowed stator makes the low-energy fluid in both cornersl move towards midspan reduces loss near end walls. The strength ability of flow field controlity at near stall condition of positive bowed stator makes an effert for the surge margin increase.While the rotor-stator axial gap of the same stage reduces, the distance between the first stator and the second rotor lengthens. The wake of the first stator dissipates exacerbattingly. It can not makes a clearly interference in the second stator’s passage. That makes the clocking effect take off. While the rotor-stator axial gap of the same stage reduces, the diffusion capability of compressor increases but the input tonque also raises. These make the efficiency of compressor improves first and falls down later. It means that there is a best axial gap wxists to make the unit get a highest efficiency. Otherwise, the ability of flow turning and through-flow decreases a little.While the axial gap reduces, the total pressure ratio of compressor with positive bowed stator increases more than the compressor with straight stator. And its input tonque raise is less than the latter. That makes the compressor with positive bowed stator get more efficiency improvement than the compressor with straight stator in small axial gap. At near stall condition, the flow field of straight stator outlet deteriorates quickly while little change occurs for the positive bowed stator. That means the flow field controlling capability of positive bowed stator gets more advantage than straight stator in small axial gap. At dedign condition, the best axial gap of compressor with positive bowed stator is smaller than the compressor with straight stator. It shows that, with positive bowed stator, the compressor can get more efficiency in less axial size. This result also can reduce the weight of the whole aero-engine.With the limitation of experiment, such as poor data size and ambiguousness of flow field in detail, the numerical simulation is done with CFX11.0. With the validation between experiment and calculation results, it shows that the calculation results can be used for qualitative analysis of flow field.Based on the topological analysis for calculation results, there are three large scale vortexs exists in compressor stator’s passge with hub tip. They are the passage vortex at up side, the scraping vortex near hub tip and the concentrated shed vortex. There ara also several small scale votex exists, such as the horseshoe vortex at the pressure side, the corner vortex at the pressure side, the vortex near the outlet of up corner and some vortex in the stator’s hub tip.While the property of pressure gradient changes (from positive pressure gradient to negative pressure gradient or negative to positive),the total number of singular points will increase and the flow field becomes complex. Sooner or later, while the fluid“fits”the pressure gradient, the structure of flow field changes simply. If there is no change for property of pressure gradient, the total number of singular points will keeps a stable value. Before the separation happens, the total number of singular points increases while the mass flow reduces in compressor stator’s passage. The total number of singular points gets the maximal value while the separation happens. When the mass flow reduces continuely, the total number of singular points begins to reduce and the flow field begins to change simply. That means in a special point of view, the flow field will be simple while the separation exacerbates. And the results of experiments in different work condition also prove this conclusion.更多还原