Work Package 2
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| State-of-the-art HP turbines are
operated at stage pressure ratios which lead to supercritical flow
conditions in the stator as well as in the rotor. A continuously
increasing thermal load due to increasing turbine inlet temperatures
accompanies the high aerodynamic load. An intense cooling of the
airfoils´ trailing edges — often the life limiting region of an airfoil
— becomes indispensable. At the same time, trailing edges need to be as
thin as possible due to the pronounced effect of trailing edge
thickness on aerodynamic loss. This gives rise to an inherent conflict
between structural integrity, manufacturing constraints, and induced
aerodynamic losses of the blades and vanes leading to a strong demand
for highly efficient cooling technology in the trailing edge region. A
promising approach e.g. is a cooling configuration consisting of an
internally ribbed passage which discharges air onto the pressure side
trailing edge cutback. This work package, therefore, concentrates on further improvements of trailing edge cooling, taking into account latest research results and developments made in such cooling configurations. General objectives are an in-depth understanding of the physics of the processes involved in trailing edge cooling and to derive useful design criteria. Furthermore, a comprehensive database will be generated for CFD-validation. The work package covers various aspects of trailing edge cooling. Beginning with further design variations of internal cooling channels and its effects on pressure drop, film cooling effectiveness and heat transfer on the cutback surface, the scope will be directed towards the influence of external supersonic flow on trailing edge cooling performance. Since these investigations will be performed in generic test set-ups, transonic cascade tests will serve as proof of the design principles derived. Intensified internal heat transfer and enhanced film cooling effectiveness on the cutback surface both allow for reduced coolant mass flows and/or reduced blade material temperatures. These achievements have a direct positive impact on efficiency and service life of HP turbines. |