【作者】 杜娟；

【导师】 黄伟光； 林峰；

【作者基本信息】 中国科学院研究生院（工程热物理研究所） ， 动力机械及工程， 2010， 博士

【摘要】 压气机／风扇转子叶顶泄漏流动对压气机性能和稳定性有着极其重要的影响,近十年来,人们发现叶顶泄漏流的存在不仅与转子失速先兆有着密切联系,而且在近失速工况附近,叶顶泄漏流还表现出明显的非定常波动特性。因此,对压气机,尤其是被广泛应用的跨音速轴流压气机／风扇转子叶顶的非定常泄漏流动进行深入研究,并在此基础上寻找高效的扩稳控制方法,对于提高航空发动机及其它燃气轮机的气动性能和稳定性具有重要意义。本文以数值模拟方法为主,实验为辅,针对三个跨音速转子叶顶非定常泄漏流动进行研究,揭示了叶顶泄漏流的非定常特征、波动机理、起始机制和空间结构,并探索叶顶泄漏流非定常性与旋转失速之间的关系。本文的核心内容主要分为以下几个部分：(1)研究叶顶泄漏流非定常特征,证实叶顶泄漏流非定常性在跨音转子中的普遍存在性；(2)阐明跨音速转子叶顶泄漏流非定常波动机理和起始机制；(3)分析跨音速转子叶顶泄漏流动的三维空间结构；(4)探索泄漏流前缘溢出机制及其与叶顶泄漏流非定常性的关系。本文首先针对三个跨音速转子叶顶泄漏流进行非定常数值模拟,介绍三个跨音速压气机／风扇孤立转子在设计间隙下,叶顶泄漏流动的非定常特征,包括频率特征、波动强度分布和叶顶瞬态流场分布,验证了叶顶泄漏流非定常性在跨音速转子中的普遍存在性。三个跨音速转子叶顶泄漏流的非定常波动特征主要体现在两个方面：一是叶片压力面上一对高、低压区沿弦向向通道下游移动,二是叶顶泄漏涡涡核轨迹起始位置和方向的摆动。这种不依赖于外界非定常边界条件而存在的非定常性,被称为自激非定常性。针对Darmstadt转子叶顶泄漏流非定常性得到的实验结果非常接近数值计算结果,在实验环境下证实了叶顶泄漏流自激非定常性的存在。在对跨音速叶顶泄漏流非定常特征有一定认识的基础上,本文第二部分进一步深入分析了叶片顶部区域负载与泄漏流速度之间的关系,发现叶顶泄漏流非定常波动机理是主流与泄漏流之间的动态相互作用。通过对比NASA-67跨音速转子在相同间隙不同流量工况、相同流量不同间隙工况下叶顶流场的非定常特征,提出叶顶区域流动发生非定常波动的两个必要条件：1)泄漏涡轨迹影响区抵达相邻叶片压力面；2)泄漏流强度足够大,能够与主流抗衡并达到稳定的动态平衡状态。通过总结各转子叶顶流场参数,进而提出间隙区域泄漏流与主流动量比和间隙大小能够用来界定泄漏流非定常性的起始机制。对于不同转子,在相同间隙条件下,随流量的减小,叶顶泄漏流与主流的动量比增加,只有当动量比达到临界值时,叶顶区域流动才会发生非定常波动。在第三部分,本文研究了跨音速转子叶顶泄漏流的三维空间结构及其与时间非定常波动特征的关系。针对三个跨音速转子,利用在间隙中部释放粒子的轨迹线分析叶顶泄漏流的三维空间结构,发现根据叶顶负载分布,叶顶泄漏流沿弦长方向可以被分为两个部分,第一部分泄漏流称为主泄漏流,具有较强的负轴向速度,第二部分泄漏流称为次泄漏流,负轴向速度几乎为零。主泄漏流在叶片前缘泄漏后,卷起形成泄漏涡,泄漏涡与主流相互作用决定了交界面的起始位置和发展方向。主泄漏涡在向通道下游移动过程中,泄漏涡影响区域向轮毂方向偏移。次泄漏流在上游主泄漏流的“保护”作用下,越过主泄漏流,抵达相邻叶片压力面,形成了体现非定常波动特征之一的局部低压、低速区域,决定了泄漏流／主流交界面在叶片压力面附近的位置。主、次泄漏流的划分位置在不同几何转子中有所不同。在此基础上,本文提出描述跨音速转子中叶顶泄漏流三维空间结构的模型示意图。在第四部分,本文通过数值计算和实验验证了泄漏流与主流交界面溢出是失速先兆发生的必要条件,并揭示了叶顶泄漏流前缘溢出机制与泄漏流自激非定常性起始机制的关系。首先通过实验在机匣上测量零轴向剪切应力线来确认泄漏流与主流的交界面,发现当交界面溢出叶片前缘后,压气机顶部开始出现先兆信号,随后进入失速状态。同时利用不同进口畸变条件研究了泄漏流与主流交界面位置和泄漏流／主流轴向动量比之间的关系,发现泄漏流与主流轴向动量比是叶顶泄漏流与主流交界面前缘溢出的机制,该机制与叶顶泄漏流非定常性起始机制一致。以上四个方面的研究内容主要从跨音速转子叶顶泄漏流的非定常特征和三维空间结构两个方面入手,全面分析了跨音速转子叶顶泄漏流的非定常机制,并通过泄漏流与主流的动量比揭示了叶顶泄漏流非定常性与失速先兆机制的同源性。更多还原

【Abstract】 A numerical and experimental study was conducted to investigate the unsteady tip leakage flow in three transonic compressor/fan rotors, with a hope to illustrate the unsteady features, reveal the originating mechanism, uncover the 3-D structure of tip leakage flow, and explore the link between the unsteady tip leakage flow and rotating stall.First of all, the existence of the unsteady tip leakage flows in three different transonic compressor/fan rotors was validated by numerical simulation and experiment. The unsteady features of tip leakage flow such as oscillating frequency, distribution of fluctuating strength, and instantaneous flow fields were studied. It was found that for all the three transonic rotors investigated, there were two main unsteady features of tip leakage flow:(1) the high-pressure spot washed down the low-pressure spot along blade pressure side, and (2) the trajectory of tip leakage vortex oscillated and thus changed the location of the low-pressure spot on the blade pressure side. This kind of unsteadiness was called self-induced unsteadiness because it emerged without external unsteady excitation.The fluctuation of pressure distribution and tip leakage velocity indicated that the mechanism of fluctuating tip leakage flow was the dynamic interaction between the incoming main flow and the tip leakage flow. An in-depth analysis of the unsteady flow fields was performed, and two necessary conditions for the initiation of unsteady tip leakage flow were proposed. One was that the region influenced by the tip leakage flow should reach the pressure side of the neighboring blade, and the other was that the tip leakage flow should be strong enough to interact with incoming main flow in order to achieve the dynamic balance. It was also found that the momentum ratio between tip leakage flow and incoming main flow and the tip clearance size could be used to quantify the initiating condition for the unsteadiness of tip leakage flow.The three-dimensional flow structure of tip leakage flow was studied by utilizing the pathline of the particles artificially released from the tip clearance region. The in-depth analysis of three-dimensional flow structures revealed three features:(1) there existed an interface between the incoming main flow and the tip leakage flow, (2) the tip leakage flow could be divided into two parts according to the blade loading distribution, and (3) each part played a different role in the location of the interface between the incoming main flow and tip leakage flow. A model of three-dimensional flow structures of tip leakage flow was thus proposed accordingly.Finally, a surface streaking method was used to experimentally examine the surface shear pattern on the casing. A region of zero axial shear stress was found to move upstream while decreasing flow coefficient. This phenomenon was also captured by numeical simulation. The compressor stalled once the zero-shear-stress line moved upstream of the blade leading edge for all cases. Inlet distortion was experimentally and numerically varied to alter the momentum ratio at the blade tip and the resulting location of the zero-shear-stress line was exmined. For all cases tested, the zero-shear stress line was observed to be at the same axial location just prior to stall. At the same mass flow rate, the the zero-shear-stress line is closer to the leading edge of the blade with tip inlet distortion than with hub inlet distortion, perhaps due to that the momentum ratio of tip leakage flow to incoming flow with tip inlet distortion is larger than that with hub inlet distortion.更多还原