Transpiration cooling for jet engine turbines

喷气发动机的第一涡轮级暴露在燃烧气体的极端温度下。在喷气发动机的整个发展过程中，冷却技术已应用于涡轮叶片，以提高进口气体温度（根据热力学第二定律提高效率）。冷却剂的使用使系统的效率降低。因此，所采用的冷却技术旨在提高涡轮进口温度，同时使用最少的冷却剂来保持合适的材料温度。蒸腾冷却是指冷却剂通过多孔壁进入气流的边界层。这直接冷却了墙壁，因为它通过，然后提供了一个表面上的冷却气体的绝缘层，减少了热流进入墙壁。它被广泛认为是最终的对流冷却解决方案，但由于缺乏合适的多孔材料和建模困难，在喷气发动机中的应用有限。然而，高温研究中心（HTRC）最近的一项发展将使制造具有可控孔隙度的涡轮叶片成为可能。该项目旨在利用这种新的制造技术来了解发动机条件下涡轮叶片的蒸腾冷却性能。主要目的是减少冷却剂，同时保持允许的材料温度。为了实现这一目标，将设计一种新的高温风洞，以产生与发动机相似的条件。将在风洞中使用氦气和空气的混合物来增加测试气体的导热性。这将提高测试叶片温度曲线与发动机条件的相似性。在整个项目中，HTRC将生产多个测试件，以测试开发设计的性能。该项目属于EPSRC工程研究领域。它与伯明翰大学高温研究中心以及劳斯莱斯公司合作。

The first turbine stage in a jet engine is exposed to the extreme temperatures of the combustion gases. Throughout the development of jet engines cooling technologies have been applied to the turbine blades to enable higher inlet gas temperatures (increases efficiency following the 2nd law of thermodynamics). The use of a coolant introduces efficiency losses into the system. Therefore the employed cooling technologies aim to enable higher turbine inlet temperatures while using the minimum amount of coolant to maintain a suitable material temperature.Transpiration cooling is where the coolant is fed though a porous wall into the boundary layer of the flow. This cools the wall directly as it passes through then provides and insulating layer of cooler gas on the surface reducing the heat flux into the wall. It is widely recognised as the ultimate convective cooling solution but has seen limited application in jet engines due to the lack of suitable porous materials and the difficulties in modelling. However a recent development at the High Temperature Research Centre (HTRC) will enable the manufacture of turbine blades with a controlled porosity.This project aims to utilize this new manufacturing technique to gain understanding in the transpiration cooling performance of turbine blades under engine conditions. With the main objective of reducing the coolant while maintaining allowable material temperatures.To achieve this a new high temperature wind tunnel will be designed to produce conditions similar to those in the engine. A mixture of helium and air will be used in the wind tunnel to increase the thermal conductivity of the test gas. This will improve the similarity of the test bladed temperature profiles to engine conditions. Multiple test pieces will be produced at HTRC throughout the project to test performance of the developed designs.This project falls within the EPSRC Engineering research area. It is in collaboration with the High Temperature Research Centre at the University of Birmingham and also with Rolls-Royce plc.