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

燃气涡轮机设计者面临的主要挑战是防止热（1300- 1800 K）主环形流进入涡轮机盘（转子）与其相邻壳体（定子）之间的叶轮空间。设计人员倾向于使用复杂的边缘密封设计，并转移相对密集的密封剂流（800 K），以避免在燃气涡轮机中发生这种情况。密封不充分会导致热气进入轴距深处，并可能导致部件过早失效和寿命有限，过度密封会导致发动机效率降低，这将导致其在燃料价格上涨和强调CO2排放的世界中失去竞争力。在巴斯进行的热气体入口的初步研究采用CO2作为示踪气体在等温条件下（300 K）。早期的结果表明，当热主流和冷密封流之间的密度比没有正确建模时，边缘密封有效性会显著降低，展示了在行业内产生重大影响的潜力。这项博士研究将主要在大型环空钻机（LAR）中进行并试图研究吹扫流和主环空流之间的密度比对进入转子的影响，几何比例工业涡轮机级定子腔。这将通过一些个别考虑来实现。首先，LAR需要一个新的收集系统，允许对出口涡流不敏感的密度比进行基础研究。LAR中可用的仪表也将重新配置，以包括高频压力传感器。此时，将通过改变吹扫流的CO2组成开始对密度比进行研究。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着影响。然后，将通过使用体积流速仪（VV）测量来进一步补充（和验证）计算流体动力学，以确定流动结构。第一个方面，将调查的是存在的叶片和叶片的密度比的影响。这将通过在转子和定子上使用简单的无叶片环进行实验和模拟来实现，然后将转动叶片引入定子，并将叶片引入转子。这将在CFD中同时建模，先没有叶片或叶片，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，使用所获得的知识，比例模型和方程将被开发，可用于工业在初步设计阶段，这将是不经济和不切实际的，由于设计的快速发展，使用CFD。

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.