Transpiration cooling for jet engine turbines

点击翻译按钮获取中文摘要

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.