Estimation of Burner Can-Induced Excitation Levels in an Industrial Gas Turbine

Abstract

Burner cans lead to a flow field at the turbine inlet with higher temperature gradients than in annular combustors. The circumferential unevenness of the temperature can become a relevant source of harmonic excitation on the downstream rotor blades. The main purpose of this work is to estimate the forcing levels of the burner can excitations on blades through the entire turbine, i.e., not only the blades immediately downstream of the burners cans are of interest. Both the compressor turbine and the power turbine are modeled in a unique setup using 3D unsteady flow simulations. Two relevant turbine inlet temperature distributions are considered. The high cycle fatigue risk due to the excitation from the burner can harmonics is assessed for the last stage rotor blade. The obtained results show that the hot streaks constitute an important source of excitation, but that the stress level of this blade can be expected to stay below the fatigue limit. A further phenomenological study is conducted in order to understand the annular flow unevenness propagation along the stages. The hot streak-induced flow perturbations are found to vary considerably in both annular and span-wise directions. The blade force stimuli of the first burner can harmonic are found to remain on the same order through the turbine, while the second harmonic stimuli exhibit a one-order decay. The possibility to use simplified models to predict burner can excitation is discussed and found less promising.