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将继续下去。航空业和政府都表示，只有航空业的环境绩效得到改善，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，要求他们生产更清洁、更高效的产品。大多数民用客机都由涡轮风扇喷气发动机提供动力。这些发动机中的所有能量输入都是通过在燃烧室中燃烧燃料来引入的。燃烧室的设计旨在最大限度地提高燃料释放的热量，同时最大限度地减少污染物的产生。燃烧器中的气体温度可大于2000摄氏度，这远高于燃烧器的金属部件的熔点。为了防止燃烧室过热和熔化，必须以某种方式冷却它。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，该空气作为薄膜沿着暴露于热气体的表面供给：这被称为薄膜冷却。燃烧室中的空气流动极其复杂，并且是高度湍流的。大的涡流通过燃烧室，产生不稳定的流动，周期性地撕裂冷却膜，使燃烧室壁暴露在非常热的气体中。燃烧室设计人员和研究人员仍然不完全了解热燃烧流对冷却膜的影响方式，这种情况阻碍了提高性能和实现排放目标的努力。低排放燃烧器使用稀燃技术，其中更多的空气与燃料混合，降低火焰温度。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传递到燃烧室壁。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设计用来模拟低排放气体涡轮机燃烧室中气流的新风洞。它还需要应用先进技术，如激光流速测量以及测量向墙壁传热的技术。通过使用先进的数据分析，将有可能了解非定常流场是如何与冷却膜相互作用的，以及为什么壁的热传递受到影响。该项目还将产生传热和流动条件之间的相关性，可供发动机制造商在新飞机发动机的设计过程中使用。它也将被用来评估冷却技术在未来新的低排放燃烧室设计中需要如何发挥作用。这项工作将应用于新的燃气涡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有助于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研究的研究人员。最后，降低航空排放的工作将通过减少航空业对环境的影响而使公众受益。

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.