Computational and Experimental Study of Hot Streak Transport Within the First Stage of a Gas Turbine

This paper discusses the migration, the interaction with the blades, and the attenuation of hot streaks generated by combustor burners, during their propagation within the first turbine stage of aero-engines. Experiments and Computational Fluid Dynamic (CFD) simulations were carried out in the framework of the European Project RECORD and on its follow-up. Measurements considering burner-representative temperature perturbations injected upstream of an un-cooled high-pressure gas turbine stage have been performed in the high-speed closed-loop test-rig of the Politecnico di Milano (Italy). The prescribed hot streaks were injected in streamwise direction at the stage inlet in four different circumferential positions with respect to the stator blade. They feature a 10-to-20% over-temperature with respect to the main flow. Detailed temperature measurements as well as unsteady aerodynamic measurements upstream and downstream of the blade rows were performed. Steady-state and time-accurate CFD simulations of the flow upstream and within the turbine stage were performed with the TRAF code, developed by the University of Florence. Measurements show a relevant attenuation of hot streaks throughout their transport within the stator and the rotor blade rows, highly depending on the injection azimuthal position. The perturbations were observed to lose their spatial coherence, especially in the transport within the rotor, and to undergo severe spanwise migration. Simulations exhibit a good agreement with the experiments on the measurement planes and allow tracking with high level of detail the complex flow phenomena occurring within the blade rows. By virtue of the combination of experiments and simulations, the aerodynamic and thermal implications of the temperature perturbations injected upstream of the stage are properly highlighted and discussed.