Stability Prediction of the Nuclear Turbine Blades During Wet Steam Nonequilibrium Condensation Process

Abstract

Stability of the nuclear turbine blades is difficult to be accurately predicted because the wet steam load (WSL) as well as its induced equivalent damping and stiffness during nonequilibrium condensation process (NECP) is hard to be directly calculated. Generally, in design, NECP is assumed as equilibrium condensation process (ECP), of which the two-phase temperature difference (PTD) between gaseous and liquid is ignored. In this paper, a novel method to calculate the WSL-induced equivalent damping and equivalent stiffness during NECP based on the combined microperturbation method (MPM) and computational fluid dynamics method (CFDM) was proposed. Once the WSL-induced equivalent damping and equivalent stiffness are determined, the stability of the blade-WSL system, of which the blade was modeled by a pretwisted airfoil cantilever beam, can then be predicted based on the Lyapunov's first method. Besides, to estimate the effects of PTD, comparisons between the WSL-induced equivalent damping and equivalent stiffness as well as the unstable area during NECP and ECP were presented. Results show that the WSL-induced equivalent damping and equivalent stiffness during NECP are more sensitive to the inlet boundary due to the irreversible heat transfer caused by PTD during NECP. Accordingly, the unstable area during NECP is about three times larger than during ECP.