Cellular Thermodynamic Model for Gas Turbine Blade Cooling

摘要

A thermodynamic model of gas turbine blade cooling was developed and used for the comparison of several coolant mediums. The model is based on a classical approach to the cooled gas turbine expansion, but it works with a micro steps cooling path. It divides the cooled expansion process in several elemental cellules (i.e. "cellular"), into which the blade cooling process is schematized as the sum of several serial elemental stages with fixed expansion temperature drop. For each of these micro stages, the related coolant mass flow rate is calculated, down to the allowable metal temperature level. The model's parameters were tuned on two different gas turbines simulation codes and the related results were compared and discussed, with reference to the film cooling technique: a satisfactory agreement was found. The procedure was applied to test the effectiveness of different cooling media: the air, the CO{sub}2, and a CO{sub}2 rich mixture from semi closed gas turbine configurations (SCGT). Moving from low to high CO{sub}2 content in the coolant, the overall gas cycle performances undergo a significant increase, mainly due to the lower coolant temperature level at the compressor outlet, that allows the use of reduced coolant mass flows. Finally, the exergy analysis was carried out, showing that the main loss source is due to the mixing process: for this reason, the cooled expansion performances are reduced moving toward high CO{sub}2 content mixtures, while a good compromise was found for the SCGT coolant type.