先进燃气透平组合冷却技术中的流-固-热耦合问题研究

In modern aviation engines, turbine blades are imperiled by the joint action of external high temperature and high speed gas from combustion with internal cooling air, which results in complex fields of temperature and thermal stress within the blade structure. This is a typical kind of fluid-thermal- structural problems. It is very important to understand and master the mechanism of the fluid-thermal-structural coupling problems in the development process of new generation aviation engines. This project will discuss the characteristics of convective heat transfer at the boundary and condutive through the interior of typical combined cooling structures, study the energy conversions and dissipation of fluid and structure, describe quantitatively the coupling relationship of conservation type between partial differential equations, analyze and complete the mathematic models of the fluid-thermal-structural coupling problems. Through PIV　experimental technique of fluid flow visualization,coolant flow performances will be investigated. Through the experiments conducted in high temperature wind tunnel, infrared thermal image and membrane techniques,the effects of mainstream and cooling air on the structures can be captured, and the real cooling effectiveness contributed by different ways, such as impingement, film coverage and rib-enhancement,will be measured. Based on the experimental data, the mathematic models and numerical strategies to solve the coupled partial differential equations can be confirmed. Using the confirmed models and numerical strategies, the heat exchange performances of different cooling structures can be calculated. Based on the analysis of the large amount of the numerical results, a scientific evaluation system regarding the losses of cooling air mass, pressure and thermal stress will be established, and a new concept of multidisciplinary optimization design will be developed.

现代航空发动机的透平叶片同时受到外部高温高速燃气与内部低温冷却气体的共同作用，因此在结构内部形成复杂的温度场和应力场。掌握这种流-固-热耦合作用蕴含的机理是研发新一代燃气透平的关键。本课题将从分析典型叶片结构内部及冷、热界面耦合传热方式着手，分析固体内能与流体总焓及耗散之间的守恒关系，量化守恒型微分方程组之间的耦合强度，研究能够清晰表述流-固-热耦合作用的数学模型。通过激光离子图像测速技术，研究流体在复杂通道中的运动及阻力模型；通过高温风洞及红外热像技术进行冷、热气流与结构换热实验，研究影响冷却效率和结构热响应的关键参数。以实验数据为支撑，完善描述冷、热气流与固体耦合作用的数学模型。分析场与场之间的耦合响应特征，寻求有效的数值途径，求解非线性耦合微分方程组。以经过验证的模型和途径，建立与冷却效率相关的压力损失、结构热响应综合评估体系。探索多参数优化设计理念，发展全新的组合冷却结构评估体系。

在基金项目的支持下，我们开展了典型组合冷却结构中的流动及换热特性机理实验及真实环境下的数值研究。首先，利用PIV及TR-PIV技术，展现叶栅通道中各种旋涡产生、发展及消失过程；利用PLIF技术，记录叶栅通道中旋涡与冷气的相互作用及其对气膜覆盖特性的影响。针对旋涡附近单纯气膜冷却效果不佳的问题，我们提出film + ramp + swirling cooling组合冷却新概念；针对瞬态涡引起的大面积烧蚀问题，我们论证了converging slot-hole变截面气膜孔优化设计。同时，利用精确可控的高温风洞及远红外热像系统，实验研究了叶栅端壁气膜、冲击及肋化组合冷却特性，分析了影响耦合传热的综合冷却效率关键因素。接着，以实验数据为依据，完成冷、热气流与固体耦合作用的数学模型、湍流模型选取、数值网格技术及动量与能量方程耦合迭代求解策略的论证。利用经过实验数据验证的数学模型和数值策略，开展真实燃气透平运行环境下的组合冷却特性数值研究，比较各种组合冷却在端壁及叶片不同部位的流阻及冷却特性；讨论燃气湍流度对气膜冷却与不同热障涂层策略（不同部位变厚度）组合冷却特性的影响。此外，利用数值方法，预测了3种广泛使用的简化实验模型导致的偏差：1）在无相对运动的环境下，研究转子叶片顶部泄漏流；2）以密度比代替温度比，研究气膜覆盖特性；3）以平面叶栅端壁代替真实的环形叶栅端壁，研究端壁气模冷却特性。在项目执行期间，我们参与了总装AXPX沈阳606所委外项目、沈阳606所预研项目A计划及中航商发有限公司的CJ系列透平研发课题。.在完成上述研究内容的同时，我们收获了丰硕的成果。这四年来，课题组发表了学术论文44篇：杂志论文29篇（英文21篇，中文8篇），会议论文15篇（国内工程热物理年会论文4篇，国际会议11篇）。其中，1篇被评为ASME GT会议优秀论文，2篇由工程热物理学会推荐给《工程热物理学报》。