Experimental and theoretical modelling of hot-gas ingestion through gas-turbine rim seals

该提案属于EPSRC流体动力学和空气动力学（已维护）组合研究领域，将有助于提高科学界的实验能力和测量仪器知识库。这项研究的主要工业影响将是提高能源效率，这是EPSRC能源主题的一个要素。燃气涡轮机发动机是一种适应性强的动力源，已被用于各种各样的应用，从发电和喷气推进到供应压缩空气和热量。行业内的竞争以及最近政府颁布的环境法规对发动机制造商施加了压力，要求他们生产更加清洁高效的产品。控制发动机性能和生命周期运行成本的最重要参数是整体效率。高循环效率取决于高的涡轮机入口温度和压气机两端的适当高的压力比。涡轮机部件（轮叶、叶片和盘）在这些高温下的寿命主要受到蠕变、氧化或热疲劳的限制。涡轮机仅可能使用这些升高的主流气体温度（热至1800 K）来操作，因为其部件受到从压缩机获取的相对冷的空气（通常为800 K）的保护。然而，这种冷却是有代价的：多达15-25%的压缩机空气绕过燃烧，以向燃烧室和涡轮机级提供所需的冷却剂。进气是发动机设计人员面临的最重要的冷却空气问题之一，国际上已经进行了大量的研究工作，以找到可接受的设计标准。当来自主流气体路径的热气体被吸入到涡轮机盘与其相邻壳体之间的叶轮空间中时，发生进入。在系统的外围安装有边缘密封件，并且使用冷却剂的密封流来减少或防止进入。但是，密封空气过多会降低发动机效率，而过少则会导致严重过热，导致涡轮机轮缘和叶片根部受损。本文提出了一种新型的全仪表化涡轮盘试验装置，用于测量燃气轮机叶轮空间的发动机典型模型中热气体进入的流动结构和传热特性。环形单级涡轮机将产生不稳定的周向压力分布，这又将在叶轮空间中产生热空气的吸入。该装置将专门设计用于光学访问，透明的旋转和固定光盘涂有热致变色液晶，并由与光盘频率同步的频闪灯照明。这将是巴斯开发的先进热成像技术的一个新的大胆应用，并将提供定性的“热可视化”和定量测量受侵入影响的旋转和静止表面区域的传热系数。小型非定常压力传感器、测压孔、皮托管、快速响应热电偶和浓度探头也将用于密封环内以及上游和下游轴距。在实验方案的同时，在巴斯开发的新理论模型将被广泛用于分析和解释从新装置获得的实验数据。这些通用模型对任何燃气涡轮机制造商都是有用的，这里将通过将它们具体转化为西门子使用的发动机设计方法来证明这一点。这项研究将产生独特和实用的数据，可以迅速利用。通过改进二次空气系统设计，成功完成和实施这项研究，将为这家英国公司带来竞争优势。

This proposal is in the EPSRC portfolio research area of fluid dynamics and aerodynamics (maintained) and will contribute to the experimental capability and measurement instrumentation knowledge base of the science community. The primary industrial impact of the research will be improvement in energy efficiency, which is one element of the EPSRC energy theme.The gas turbine engine is an adaptable source of power and has been used for a wide variety of applications, ranging from the generation of electric power and jet propulsion to the supply of compressed air and heat. Competition within the industry and, more recently, environmental legislation from government have exerted pressure on engine manufacturers to produce ever more cleaner and efficient products.The most important parameter in governing engine performance and life cycle operating costs is the overall efficiency. High cycle efficiency depends on a high turbine entry temperature and an appropriately high pressure ratio across the compressor. The life of turbine components (vanes, blades and discs) at these hot temperatures is limited primarily by creep, oxidation or by thermal fatigue. It is only possible for the turbine to operate using these elevated mainstream gas temperatures (as hot as 1800 K) because its components are protected by relatively cool air (typically 800 K) taken from the compressor. However, this cooling comes at a cost: as much as 15-25% of the compressor air bypasses combustion to provide the required coolant to the combustor and turbine stages. Ingress is one of the most important of the cooling-air problems facing engine designers, and considerable international research effort has been devoted to finding acceptable design criteria. Ingress occurs when hot gas from the mainstream gas path is ingested into the wheel-space between the turbine disc and its adjacent casing. Rim seals are fitted at the periphery of the system, and a sealing flow of coolant is used to reduce or prevent ingress. However, too much sealing air reduces the engine efficiency, and too little can cause serious overheating, resulting in damage to the turbine rim and blade roots. It is proposed to build a new fully-instrumented rotating-disc rig to measure the flow structure and heat transfer characteristics of hot gas ingress in an engine-representative model of gas-turbine wheel-spaces. An annular single-stage turbine will create an unsteady circumferential distribution of pressure, which in turn will create the ingestion of hot air in the wheel-spaces. The rig will be designed specifically for optical access, with transparent rotating and stationary discs coated with thermochromic liquid crystal and illuminated by a strobe light synchronised to the disc frequency. This will be a new, bold application of the advanced thermal-imaging technology developed at Bath and will provide both qualitative 'thermal visualisation' and quantitative measurements of heat transfer coefficient in the regions on the rotating and stationary surfaces affected by ingress. Miniature unsteady pressure transducers, pressure taps, pitot tubes, fast-response thermocouples and concentration probes will also be used inside the seal annulus and in the upstream and downstream wheel-spaces. In parallel with the experimental programme, new theoretical models developed at Bath will be used extensively in the analysis and interpretation of the experimental data obtained from the new rig. These generic models will be of use to any gas turbine manufacturer, and here this will be demonstrated by specifically translating them into the engine-design methodology used at Siemens. The research will generate unique and practically-useful data which can be rapidly exploited. The successful completion and implementation of this research through improved secondary air system design should result in a competitive advantage for the UK-based company.