Gas turbine cooling has steadily acquired major importance whenever engine performances have to be improved. Among various cooling techniques, film cooling is probably one of the most diffused systems for protecting metal surfaces against hot gases in turbine stages and combustor liners. Most recent developments in hole manufacturing allow to perform a wide array of micro-holes, currently referred to as effusion cooling. This paper presents the validation of a simplified 2D conjugate approach through comparison with the experimental results of effectiveness for an effusion plate, performed during the first year of the European Specific Targeted REsearch Project AITEB-2 (Aerothermal Investigation of Turbine Endwalls and Blades). A preliminary test is performed with the steady-state technique, using TLC (Thermochromic Liquid Crystal) wide-band formulations. Results are obtained in terms of local distributions of adiabatic effectiveness. Average values are compared with calculations to validate the numerical code. Then, Design Of Experiment (DOE) approach is used to perform several conjugate tests (about 180), so as to derive the behavior of different effusion plates in terms of overall effectiveness and mass flow rate. Data are analyzed in detail and a correlative approach for the overall effectiveness is proposed.
Film cooling is certainly the most diffused system to protect metal surface against hot gases, both in turbogas blades and combustors. Although being very diffused, there are still several aspects of its behavior which need a better understanding. Mainly, the performance of multi-row holes configurations are still estimated correcting single-row correlations. Heat transfer coefficient modifications due to the presence of injected coolant are hard to evaluate, and even now few studies in literature take into account this factor. The present work is a detailed numerical study of some effects of film cooling. 3D CFD-RANS simulations have been performed to infer interesting trends of adiabatic superposition effects and conjugate heat transfer performances. In particular, several calculations have been carried out to evaluate single row and multi-row film cooling behavior in terms of heat transfer coefficient, overall and adiabatic effectiveness. Test were conducted with blowing ratios between 0.5 and 5.5, coolant Reynolds from 1000 to 16000.
The aim to reach very low emission limits has recently changed several aspects of combustor fluid dynamics. Among them, combustor cooling experienced significant design efforts to obtain good performances with unfavorable conditions. This paper deals with experimental research and 1D numerical simulations of impingement cooling from multiple jet arrays, performed in the first two years of the European research project LOPOCOTEP. Geometries are derived from typical LPP combustor cooling configurations, i.e. small and sparse holes, due to low coolant mass flow rate and high pressure losses (compared to typical blade cooling parameters). Tests are performed with both transient and steady-state technique, using TLC (Thermochromic Liquid Crystal) wide-band formulations. Results are obtained in terms of local distributions of heat transfer coefficient and effectiveness. Average values are compared with calculations to validate numerical code and derive useful indications on effectiveness variation for different blowing rate. It is accordingly found that literature results almost match the measurements. It is also shown that measured row-by-row effectiveness values can be usefully employed in a preliminary design stage. Data concerning holes discharge coefficients are also presented.
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