Measurement and modelling of ingress through gas turbine rim seals

燃气轮机发动机是一种适应性很强的动力源，已被广泛应用，从发电和喷气推进到提供压缩空气和热量。行业内的竞争，以及最近政府的环境立法，都对发动机制造商施加了压力，要求它们生产更清洁、更高效的产品。控制发动机性能和生命周期运营成本的最重要参数是整体效率。较高的循环效率取决于较高的涡轮入口温度和压缩机上适当的较高压力比。涡轮部件(叶片、叶片和轮盘)在这些高温下的寿命主要受蠕变、氧化或热疲劳的限制。涡轮机只能使用这些较高的主流气体温度(高达1800K)运行，因为其部件受到来自压缩机的相对较冷的空气(通常为800K)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，为燃烧室和涡轮级提供所需的冷却剂。进气是发动机设计者面临的最重要的冷却空气问题之一，国际上已有大量的研究工作致力于寻找可接受的设计标准。当来自主流气体路径的热气体被吸入涡轮盘与其相邻机壳之间的轮隙时，就会发生入口。在系统的外围安装了轮缘密封件，并使用冷却液的密封流来减少或防止进入。然而，太多的密封空气会降低发动机的效率，太少的密封空气会导致严重的过热，导致涡轮轮缘和叶片根部损坏。提出了建立一种新的转盘试验台，用于测量燃气轮机轮室发动机代表模型中热气体入口的流动结构和换热特性。该钻机将采用通用发动机几何结构；它将完全配备仪器，并专门为光学访问而设计。环形单级涡轮将产生不稳定的周向压力分布，这反过来又会在车轮空间产生热空气的吸入。快速响应热电偶和热致变色液晶与频闪光相结合将用于热瞬变实验，以测量转盘、定子和钻机轮隙内空气的温度。微型压力传感器、压力接头、皮托管和浓度探头也将在密封环内和车轮空间中使用。此外，还将利用收集到的实验数据建立并验证入口的理论模型。这个入口模型将被用来获得冷却效率和表面温度之间的关联式。更广泛地说，这项研究将为燃气轮机进口的热效应提供基本的见解，并反过来为内部空气系统的设计提供信息。

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 rotating-disc rig to measure the flow structure and heat transfer characteristics of hot gas ingress in an engine-representative model of a gas-turbine wheel-space. The rig will feature generic engine geometries; it will be fully-instrumented and specifically designed for optical access. 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-space. Fast-response thermocouples and thermochromic liquid crystal in conjunction with a stroboscopic light will be used in thermal transient experiments to measure the temperature of the rotating disc, the stator and the air inside the wheel-space of the rig. Miniature pressure transducers, pressure taps, pitot tubes, and concentration probes will also be used inside the seal annulus and in the wheel-space. In addition, a theoretical model of ingress will be developed and validated using the experimental data collected. This ingress model will be used to obtain correlations of cooling effectiveness and surface temperatures. More generally, the research will provide fundamental insight into the thermal effects of ingress in gas turbines and in turn inform the design of internal air systems.