Unsteady flow effects on film cooling in low-emissions gas turbine combustors

在可预见的未来，商业航空的强劲增长势必会持续下去。航空业和政府都表示，只有随着航空商业部门环境表现的改善，这种扩张才是可持续的。这给飞机发动机制造商带来了压力，要求它们生产更清洁、更高效的产品。大多数民用客机都由涡扇喷气发动机提供动力。这些发动机的所有能量输入都是通过在燃烧室中燃烧燃料来引入的。燃烧室的设计是为了最大限度地增加燃料释放的热量，同时也最大限度地减少污染物的产生。燃烧室中的气体温度可以高于2000摄氏度，这远远高于燃烧室金属部件的熔点。为了阻止燃烧器过热和潜在的融化，必须以某种方式对其进行冷却。这是通过使用来自发动机压缩机的相对较冷的空气来实现的，这些空气以薄膜的形式沿着暴露在热气体中的表面输送：这被称为薄膜冷却。燃烧室内的气流极其复杂，具有很强的湍流性。巨大的漩涡穿过燃烧室，产生一种不稳定的流动，周期性地撕裂冷却膜，使燃烧室壁暴露在非常热的气体中。燃烧室的设计者和研究人员仍然没有完全了解热燃烧流对冷却膜的影响方式，这种情况正在阻碍提高性能和实现排放目标的努力。低排放燃烧器使用稀薄燃烧技术，将更多的空气与燃料混合，降低火焰温度。这意味着可用于冷却燃烧室壁面的空气更少。本项目的总体目标是研究低排放燃烧室的流体动力学，并了解这如何影响热量传递到燃烧室壁面。该项目将提供有关各种参数如何影响复杂流动的详细信息。这就需要建造一个专门为模拟低排放燃气轮机燃烧室内的流动而设计的新风洞。它还需要应用先进的技术，如基于激光的流速测量以及测量墙体热传递的技术。通过使用先进的数据分析，将有可能了解非定常流场如何与冷却膜相互作用，以及为什么壁面的换热会受到影响。该项目还将在传热和流动条件之间建立关联，供发动机制造商在新飞机发动机的设计过程中使用。它还将被用来评估新的低排放燃烧室设计的冷却技术在未来的表现。这项工作将应用于新的燃气轮机燃烧系统的开发。这将使发动机制造商直接受益。更好的理解将有助于制造商更好、更快地进行设计，减少所需的冷却空气量，从而有助于减少污染物排放。该项目产生的数据将帮助该领域的其他研究人员，特别是那些正在研究基于计算的燃烧室流动调查的人。最后，这项工作对降低航空排放量的贡献将通过减少航空业对环境的影响而惠及公众。

The strong growth in commercial aviation is set to continue for the foreseeable future. Both the aviation industry and government state that this expansion is only sustainable with the improved environmental performance of the aviation business sector. This is placing pressure on aircraft engine manufacturers to produce cleaner, more efficient products. Most civil airliners are powered by turbofan jet engines. All of the energy input in these engines is introduced by burning fuel in a combustor. The combustor is designed to maximise the heat liberated from the fuel whilst also minimising the generation of pollutants. Gas temperatures in the combustor can be greater than 2000 centigrade and this is well above the melting point of the metal components of the combustor. To stop the combustor from overheating and potentially melting, it must be cooled in some way. This is achieved by using relatively cool air from the engine's compressor which is fed as a film along the surfaces exposed to the hot gases: this is known as film-cooling. The air flow in a combustor is extremely complex, and is highly turbulent. Large vortices pass through the combustor, giving an unsteady flow that periodically rips off the cooling film and exposes the combustor walls to very hot gases. Combustor designers and researchers still do not fully understand the way in which the cooling film is affected by the hot combusting flow, a situation that is hampering efforts to improve performance and achieve emissions targets. Low-emissions combustors use lean-burn technology where more air is mixed with the fuel reduce the flame temperatures. This means that less air is available for cooling the combustor walls.The overall aim of this project is to investigate the fluid dynamics of a low-emission combustor, and to understand how this affects the transfer of heat to the combustor walls. The project will deliver detailed information on how various parameters affect the complex flows. This requires the building of a new wind-tunnel that is specifically designed to simulate the flows in low-emission gas turbine combustors. It will also require the application of advanced techniques such as laser-based flow velocity measurement as well as technologies for measuring the heat transfer to the walls. By using advanced data analysis it will be possible to understand how the unsteady flow-field is interacting with the cooling films and why the heat transfer to the walls is affected. The project will also generate correlations between heat transfer and flow conditions that can be used by engine manufacturers in the design process of new aircraft engines. It will also be used to estimate how cooling technologies will need to perform in the future with new lower emissions combustor designs.This work will be applied in the development of new gas turbine combustion systems. It will benefit engine manufacturers directly. The improved understanding will contribute to better and faster design by manufacturers, reducing the amount of cooling air needed and thereby helping to reduce pollutant emissions. The data produced by the project will help other researchers in the field, particularly those who are looking at computational based investigations of combustor flows. Finally, the contribution of the work towards lower aviation emissions will benefit the public through the reduced environmental impact of the aviation industry.