LES of the T106 low-pressure turbine: Spectral proper orthogonal decomposition of the flow based on a fluctuating energy norm

This paper investigates the use of the spectral proper orthogonal decomposition (SPOD) on the flow around the T106 low-pressure turbine cascade. The chosen metric of the SPOD is based on the hydrodynamic flow disturbances for compressible flows and is used to characterize the flow structures holding large energy disturbances and synchronization processes with incoming wakes when considered. The input data for the SPOD is provided by large-eddy simulations of the T106 cascade. The Reynolds number and free-stream turbulence effects on the flow structures are studied using four operating points investigated in previous experiments and numerical simulations: Reynolds numbers of Re = 5.18 x 104 and Re = 1.48 x 105 without and with upstream wakes. The analysis of the SPOD indicates that the upstream wakes can amplify some modes of the suction side boundary layer (apparently a receptivity mechanism) and intensify the developing blade wake turbulent structures downstream of the trailing edge. This amplification happens over a reduced frequency bandwidth between Strouhal numbers equal to 7-10 for the low Reynolds number case and 20-24 for the high Reynolds number case.