Effects of Novel Combustor Geometries on the NGV for Future Flexible Operations of Gas Turbines with Flexible Fuels

多年来，燃气轮机发电的使用量大幅增加，预计2013年至2020年，全球市场将增长45%。随着不同来源的可再生能源在财务和技术上变得更加可行，能源市场也变得更加多样化。因此，燃气轮机很可能成为提供基本负荷的中流砥柱，因此需要在操作负荷以及氢和生物燃料等燃料的灵活性方面增加灵活性。未来灵活操作和燃料的一个主要挑战是燃烧室设计及其对涡轮机的影响。燃烧室通常是隔离设计和测试的，除了通过目标整体流动特性以外，几乎没有参考下游涡轮机。然后，NGV的设计依赖于入口剖面的简单模型，例如各向同性湍流强度、湍流强度剖面或在空间和时间上静止的涡流剖面。基本假设是NGV周围的流场基本上是稳定的。然而，大多数现代工业燃气轮机使用稀薄预混、旋流稳定燃烧，从而降低火焰温度，从而减少NOx的生成。漩涡是混合和稳定火焰并防止回火或回火所必需的。在旋流器的下游形成一个回流区，从而形成一个总压力较低的旋流核心，该核心持续存在于旋流器下游很远的地方，甚至对流到NGV的下游。这个中心低压核心不只是旋流器中心体的“尾迹”，而是由膨胀的过渡管道中的旋涡破裂造成的。因此，燃烧室下游的流动本质上是非定常的，并且具有大尺度相干结构的特点。这些结构对NGV的空气动力学和换热有显著影响。本文研究了不同的燃烧室旋流结构对这些流动结构的定常和非定常影响，进而研究了气膜冷却NGV的空气动力学和换热。这里给出了整个叶片上HTC的时变全表面图，清楚地解析了这些结构。这项研究中包括了一个单独的大型旁路旋流器，因为它代表了当今使用的传统旋流器。这项研究表明，这种几何形状导致了最大的结构，从而导致了HTC的最大波动。通过燃烧室设计可以减少这些影响，因此表明通过燃烧室和NGV的集成设计可以实现更大的优化。这项研究将是使用各种高速实验技术(如高速红外热像仪、薄膜压力计和高速表面贴装压力传感器)研究燃烧室流动的非定常影响的首个此类研究。还将进行高保真大涡模拟，以完全解决非定常流场。该项目属于EPSRC能源和工程研究领域。

The use of gas turbines for power generation has increased significantly over the years, with the global market predicted to grow by 45% from 2013 to 2020. The energy market is also growing more diverse as renewables from different sources become more viable financially and technologically. Gas turbines are therefore likely to become the mainstay for providing the base load, thus driving the need for increased flexibility in terms of operational load as well as flexibility of fuels such as hydrogen and biofuels.One main challenge towards this future of flexible operations and fuels is the combustor design and its effects on the turbine. Combustion chambers are typically designed and tested in isolation, with little reference to the downstream turbine except through targeted bulk flow properties. The design of the NGV then relies on simple models for the inlet profile such as isotropic turbulence intensity, a turbulence intensity profile, or a swirl profile that is static in space and time. The underlying assumption is that the flow field around the NGV is essentially steady.However, most modern industrial gas turbines use lean premixed, swirl stabilised combustion which lowers the flame temperature, thus reducing the formation of NOx. The swirl is necessary to mix and stabilise the flame and prevent flashback or backfiring. A recirculation zone is created downstream of the swirler which results in a lower total pressure swirl core that persists far downstream of the swirler and even convects downstream of the NGV.This central low pressure core is not simply the `wake' of the swirler centre body, but rather is created by so-called vortex breakdown of the swirl in the expanding transition duct. As a result, the flow downstream of a combustor is inherently unsteady and is characterised by large scale coherent structures. These structures have been shown to significantly affect the aerodynamics and heat transfer on an NGV.This study investigates the steady and unsteady effects of different combustor swirl geometries on these flow structures and consequently, the aerodynamics and heat transfer on a film-cooled NGV. Time-varying, full surface maps of HTC across the vane are presented here which clearly resolve these structures. A single large bypass swirler has been included in this study as it is representative of conventional swirlers in use today. It is shown in this study that this geometry results in the largest structures and consequently the highest fluctuations in HTC. These effects can be reduced through combustor design, hence showing that greater optimisation could be achieved through the integrated design of the combustor and NGV.This study will be the first of its kind in investigating the unsteady effects of combustor flows using various high-speed experimental techniques such has high-speed infrared thermography, thin-film gauges, and high-speed surface mount pressure transducers. High-fidelity Large Eddy Simulations will also be carried out to full resolve the unsteady flow field.This project falls within the EPSRC Energy and Engineering research area.