Nonuniformity of combustor-exit-flow temperature, also named hot-streak, could strongly increase the complexity in unsteady flow and heat transfer of gas turbine cascades. Detailed investigation into the hot-streak transportation in multi-stage gas turbine should provide a valuable reference to both fault diagnosis of combustors based on the distribution of turbine exhaust temperature.
In this study, transportation of hot-streaks inside a four-stage gas turbine was numerically investigated using three-dimensional (3D), Unsteady Reynolds Averaged Navier-Stokes equations (URANS) Computational Fluid Dynamics (CFD) study with simulation domain including eight full-annulus cascades. The two-dimensional (2D) temperature fields at the rotor-stator interfaces and turbine exit was acquired by the full-annulus URANS CFD, and then discussed through comparing the circumferential and radial distributions and also the ranges of time-dependent fluctuations. The time-average temperature distributions were analyzed by Discrete Fourier Transform (DFT) method in circumferential direction to characterize the distribution.
The URANS CFD results show that the hot-streaks could travel through the entire turbine and result in nonuniformity of turbine exhaust temperature. The rotor-stator interaction could change the 2D shape of hot-streaks and intensity the time-dependent fluctuation of flow temperature. DFT results show that the typical frequencies of circumferential temperature distribution are coinciding with the number of hot-streaks and the blade number of upstream/ downstream cascades. The DFT results also indicated that the hot-streaks migrate 35°∼45° in the circumferential direction, and the maximal relative amplitude of hot-streaks is reduced from 28% to 5%. The redistribution of hot/cold fluid in stator cascade could affect the mixing of hot-streaks depending on clocking position.