The effect of purge-mainstream density ratio on turbine cavity flows.

燃气轮机设计者面临的一个主要挑战是防止热的(1300-1800K)主环状流进入涡轮盘(转子)与其相邻的机壳(定子)之间的轮隙。设计人员倾向于使用复杂的轮缘密封设计，并改变相对稠密的密封剂流动(800K)，以避免这种情况发生在燃气轮机中。密封不足会导致热气体深入车轮空间，并可能导致部件过早故障和有限的寿命；过度密封可能会导致发动机效率降低，从而导致发动机在燃油价格上涨和强调二氧化碳排放的世界中失去竞争力。在巴斯进行的热气进入的初步研究使用二氧化碳作为示踪气体，在等温条件下(300K)。早期的研究结果表明，当热主流和冷密封流之间的密度比没有得到适当的模拟时，轮缘密封效率会显著降低，这表明在行业内可能会产生重大影响。这项博士研究将主要在巴斯大学的大型环空试验台(LAR)中进行，试图调查吹扫流和主环空中流之间的密度比对几何尺寸工业涡轮级的动静腔入口的影响。这将通过一些个人考虑来实现。首先，LAR需要一个新的收集系统，允许对密度比进行基础研究，而对出口漩涡不敏感。LAR中可用的仪器也将重新配置，以包括高频压力传感器。在这一点上，对密度比的研究将通过改变吹扫气流的二氧化碳成分来开始。为了确保这与模拟一致，将在OpenFOAM中进行定制的CFD以直接匹配实验。这种伴随的方法将旨在解开复杂的进入机制和密度比的显著影响。然后，将通过使用体积测速仪(VV)测量来识别流动结构来进一步补充(和验证)CFD。首先要研究的是叶片和叶片的存在对密度比的影响。这将通过在转子和定子上都安装一个简单的无叶片环进行实验和模拟，然后在定子上引入转动叶片，在转子上引入叶片。这将在CFD中同时建模，没有叶片或叶片，然后是叶片或叶片，最后是叶片和叶片。第二阶段将研究端壁轮廓对密度比的影响。最后，利用所获得的知识，将开发出可供工业在初步设计阶段使用的比例模型和方程，当由于设计的快速发展而使用CFD将是不经济和不切实际的。

A major challenge facing gas turbine designers is preventing hot (1300-1800K) main-annulus flows entering the wheel-space between the turbine disc (rotor) and its adjacent casing (stator). Designers tend to use complex rim seal designs and divert relatively dense sealant flows (800K) to avoid this occurring in the gas turbine. Insufficient sealing can cause hot gas ingress deep into the wheel-space and can lead to premature failure and limited life of the components, excessive sealing can cause reductions in efficiency of the engine which would lead to it becoming uncompetitive in a world of increasing fuel prices and emphasis on CO2 emissions. Preliminary studies of hot gas ingress conducted at Bath employed CO2 as a tracer gas at isothermal conditions (300K). Early results revealed a significant reduction in rim-seal effectiveness when the density ratio between the hot main flow and cold sealing flow was not properly modelled, demonstrating the potential for significant impact within industry.This PhD research will primarily be conducted in the Large Annulus Rig (LAR) at the University of Bath and seek to investigate the effect of the density ratio between the purge flow and main annulus flow on ingress into the rotor-stator cavity of a geometrically scaled industrial turbine stage. This will be achieved through a number of individual considerations. Firstly, the LAR requires a new collection system, allowing for a fundamental study of density-ratio with insensitivity to exit swirl. The instrumentation available in the LAR will also be reconfigured to include high frequency pressure transducers. At this point, investigations into the density ratio will begin by varying the CO2 composition of the purge flow. To ensure this is consistent with simulations, bespoke CFD will be conducted in OpenFOAM to directly match the experiments. This concomitant approach will aim to unravel the complex ingress mechanisms and significant effect of density ratio. The CFD will then be further supplemented (and validated) by using Volumetric Velocimetry (VV) measurements to identify flow structures. The first aspect that will be investigated is the presence of vanes and blades on the density ratio effect. This will be achieved by conducting experiments and simulations with a simple, un-bladed ring on both the rotor and stator, then introducing turning vanes onto the stator, and blades onto the rotor. This will be modelled concurrently in CFD by having no vanes or blades, then either vanes or blades and finally both vanes and blades. The second stage will look into the effects of end-wall contouring on the density ratio. Finally, using the knowledge obtained, scaling models and equations will be developed which could be used by industry during the preliminary design phase when it would be uneconomical and impractical to use CFD due to the rapid development of designs.