Thermal-structural response and low-cycle fatigue damage of channel wall nozzle

Abstract

To investigate the thermo-mechanical response of channel wall nozzle under cyclic working loads, the finite volume fluid-thermal coupling calculation method and the finite element thermal-structural coupling analysis technique are applied. In combination with the material low-cycle fatigue behavior, the modified continuous damage model on the basics of local strain approach is adopted to analyze the fatigue damage distribution and accumulation with increasing nozzle work cycles. Simulation results have shown that the variation of the non-uniform temperature distribution of channel wall nozzle during cyclic work plays a significant role in the thermal-structural response by altering the material properties; the thermal–mechanical loads interaction results in serious deformation mainly in the front region of slotted liner. In particular, the maximal cyclic strains appear in the intersecting regions of liner gas side wall and symmetric planes of channel and rib, where the fatigue failure takes place initially; with the increase in nozzle work cycles, the residual plastic strain accumulates linearly, and the strain amplitude and increment in each work cycle are separately equal, but the fatigue damage grows up nonlinearly. As a result, a simplified nonlinear damage accumulation approach has been suggested to estimate the fatigue service life of channel wall nozzle. The predicted node life is obviously conservative to the Miner’s life. In addition, several workable methods have also been proposed to improve the channel wall nozzle durability.