In this work, proper orthogonal decomposition (POD) was applied to large eddy simulations (LES) of two high-loaded low-pressure turbine cascades under unsteady inflow to investigate entropy production in different parts of the blade passage. The turbulent kinetic energy (TKE) production, diffusion, and dissipation terms from the stagnation pressure transport equation were integrated over the computational domain. The POD-based method splits the contribution of different coherent flow dynamics to TKE production and dissipation, including the migration, bowing, tilting, and reorientation of incoming wake filaments, as well as the breakup of streaky structures in the blade boundary layer and the formation of Von Karman vortices in the blade wake. This helps designers identify the dominant POD modes (turbulent flow structures) responsible for loss generation, their dynamics, and the spatial locations where they act, providing insights into the physical phenomena to be controlled. Following this optimization strategy, a new low-pressure turbine profile was designed. After performing LES on the optimized geometry, POD results indicated the possibility of designing a higher-loaded profile with a lower global loss coefficient. Thanks to the stronger acceleration imposed on 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.

In this study, a procedure based on Phase-locked Proper Orthogonal Decomposition (PPOD) was applied to Large Eddy Simulations (LES) of two low-pressure turbine blades operating with unsteady inflow. This decomposition allows the inspection of the effect of blade loading on loss generation mechanisms, especially focusing on their variation throughout the incoming wake period. After sorting snapshots based on their phase within the wake cycle using temporal POD coefficients associated with wake migration, POD was reapplied to each sub-ensemble of snapshots at a given phase, providing an optimal representation of the dynamics at fixed wake locations. This highlighted the effects of migration, bowing, tilting, and reorientation of the incoming wake filaments, as well as the breakup of streaky structures in the blade boundary layer and the formation of Von Karman vortices at the blade trailing edge. PPOD offered the opportunity to observe how all these processes are modulated and change throughout the wake period. The comparison between the two analyzed blades showed that overall loss generation follows similar temporal patterns during the wake passing cycle, increasing with the propagation of the upstream wake and reaching its maximum value when the wake is in the peak suction position. According to the specific blade loading distribution, the production of TKE was observed in different regions of the computational domain. The described procedure may contribute to the development of advanced design processes based on physically-informed strategies.

In this study, a procedure based on Phase-locked Proper Orthogonal Decomposition (PPOD) was applied to Large Eddy Simulations (LESs) of two low-pressure turbine blades operating with unsteady inflow. This decomposition allows the inspection of the effect of blade loading on loss generation mechanisms, focusing especially on their variation throughout the incoming wake period. After sorting snapshots based on their phase within the wake cycle using temporal POD coefficients associated with wake migration, POD was reapplied to each sub-ensemble of snapshots at a given phase, providing an optimal representation of the dynamics at fixed wake locations. This highlighted the effects of the migration, bowing, tilting, and reorientation of the incoming wake filaments, as well as the breakup of streaky structures in the blade boundary layer and the formation of Von Karman vortices at the blade trailing edge. PPOD offered us the opportunity to observe how all these processes are modulated and change throughout the wake period. The comparison between the two analyzed blades showed that overall loss generation follows similar temporal patterns during the wake-passing cycle, increasing with the propagation of the upstream wake and reaching its maximum value when the wake is in the peak suction position. According to the specific blade loading distribution, the production of TKE was observed in different regions of the computational domain. The described procedure may contribute to the development of advanced design processes based on physically informed strategies.