Air-cooling methods for gas-turbine combustion systems

Abstract

This paper presents an account of the whole of the work which has been done at the National Gas Turbine Establishment on the problem of air cooling gas-turbine combustion systems. Each of the different methods, of wall cooling is discussed separately and the theory and mechanism of the cooling process is developed from first principles. Certain of the methods have been the subjects of experimental investigations and in such cases a brief description of the test arrangements is given and the results are analysed arid discussed. Sufficient information is given to enable any of the various methods to be applied to practical wall-cooling problems and, in a conclusion to the report, their relative advantages and disadvantages for different gas-turbine applications are considered. It is shown that 'sweat', or effusion-cooling, is by far the most effective and efficient method, while the use of 'louvred' surfaces represents the nearest practical approach to this ideal which is possible while suitable porous materials remain unavailable. The remaining methods (convective cooling by external airflow, localised air injection to form a protective blanket of coolant, and a combination of these two), are all less effective, but provide means whereby conventional combustion systems may be conveniently cooled without the need for porous materials or the weight increases associated with louvred walls.