When designing gas turbines, a high combustion temperature is desirable to obtain a good thermal eciency. At the same time, the thermal limitations of the gas turbines components must not be exceeded. High temperatures can lead to large thermal stresses that can reduce the life span of the components and increase the risk of fatigue and failure.
The trade-o between eciency on the one hand, and reliability, life span, service interval etc. on the other hand, must be handled early in the design process. At the same time, many other aspects such as aerodynamics, structural strength, manufacturing and assembly must be considered simultaneously.
In the combustor and high pressure turbine, lm cooling is extensively used as one of the major ways to protect parts from the gases of combustion. Film cooling was introduced about 50 years ago, and is today normally actualized by taking air from the compressor and ejecting it out through rows of holes placed on the surfaces that are to be protected.
Film cooling is a complex process, in uenced by many parameters related to the hole geometry, the flow through the hole, and the free stream above the surface of interest, see e.g. A number of governing parameters have been identied, and their effect has been analyzed, see e.g.
In order to handle the design of lm cooling along with the rest of the design process, fast and relatively accurate tools for prediction and comparison of film cooling congurations are essential. One early attempt to describe film cooling by a correlation was carried out in the sixties. Since then a number of correlations have been developed and scrutinized, but most of them have considered at plates without pressure gradients, a case that is not always representative for gas turbine lm cooling. Furthermore, most correlations are developed utilizing experiments, where at least some of the parameters in the correlation have been adopted to t particular experimental data. This give rise to questions regarding, among others, the possibility to generalize the result of the correlations to other presumptions. This investigation summarize some of the correlations presented in the open literature, and discuss their strengths and weaknesses.
Linköping: Linköping University Electronic Press, 2009. , 18 p.