Impact of Turbine Blade Internal Cooling on Aerodynamic Loss

Modern gas turbines operate at high temperature, which exceed the endurance limit of material, and therefore the turbines components have to be cooled by the air taken from the compressor. The cooling providing positive impact on lifetime of GT has negative impact on its performance. Firstly because the cooling air bypasses combustor and its capacity is not fully utilized. This effect is usually accounted in thermodynamic calculations of gas turbine. Secondly the injection of cooling air in the turbine disturbs the main flow, and may lead to increased losses. In addition cooling requirements lead to limitation on the blade shape (e.g. limiting the minimal size of trailing edge) and thereby negatively affect the losses. These effects were already discussed in the literature, but further investigations for better understanding of flow physics and design improvement are still useful.There is also additional impact of cooling - impact of heat transfer on near wall boundary layer and coolant properties. This effect was not sufficiently discussed in the open literature, where quite often the walls are considered as adiabatic.The paper consists of two main parts. In the first part the results of experimental investigations of several linear cascades with and without trailing edge injection are presented and discussed.In the second part the results of detailed numerical investigations of one of these cascades are presented. One set of calculations were done at the test rig conditions for comparison with measured data. These calculations were used for validation of CFD model. The next sets of calculations were done for engine typical conditions, including the simulation of blade material temperature. The calculations were performed for adiabatic wall and for surface with heat transfer, including the impact of heat transfer on coolant injection. This analysis provides split of losses caused by different factors, and offers the opportunities for efficiency and lifetime improvements of real engine designs/upgrades.Copyright © 2015 by Alstom Technologie AG