OPTIMIZATION OF LOW-PRESSURE TURBINE BLADE BY MEANS OF FINE INSPECTION OF LOSS PRODUCTION MECHANISMS

In the present work, Proper Orthogonal Decomposition (POD) has been applied to Large Eddy Simulations (LES) of two high-loaded low-pressure turbine cascade operating under unsteady inflow for the detailed investigation of the entropy production in the different part of the blade passage. To this end, the Turbulent Kinetic Energy (TKE) production, diffusion and dissipation terms appearing into the stagnation pressure transport equation have been integrated all over the computational domain. The POD-based procedure allows splitting the contribution due to different coherent flow dynamics to the turbulent kinetic energy production and dissipation, due to the migration, bowing, tilting and reorientation of the incoming wake filaments, as well as to the breakup of streaky structures into the blade boundary layer and/or to the formation of Von Karman vortices into the wake of the blade. This enables a designer to identify the dominant POD modes (i.e., turbulent flow structures) responsible for loss generation mechanisms, their dynamics and the spatial locations where they mainly act, thus providing a deep view on the physical phenomena to be controlled. Following this optimization strategy, a new low pressure turbine profile has been designed. After running a LES calculation on the new optimized geometry, POD results showed that it is possible to design a higher-loaded profile which operate with a lower global loss coefficient. Thanks to stronger acceleration imposed to the bulk flow in the former part of the blade passage, the new loading distribution is shown to be responsible for lower upstream wake migration losses, as well as for a smaller amount of TKE production in the trailing edge wake zone, as a result of the early suction side boundary layer transition.