Large Eddy Simulation-Based Time–Frequency Characterization of Vortex–Pressure Coupling in an Axial-Flow Nuclear Reactor Coolant Pump Impeller

Abstract This study is based on three-dimensional large eddy simulation (LES) and time–frequency coupled analysis to provide an in-depth investigation of pressure pulsations and vortex structure mechanisms within the impeller passage of the nuclear reactor coolant pump (NRCP). By introducing continuous wavelet coherence analysis, the evolution of the pressure pulsation signals in the time–frequency domain was examined; the local coherence between the Q criterion and pressure pulsation signals was evaluated, revealing that the local coherence at the impeller inlet is higher than at the impeller outlet, indicating that the vortex–pressure coupling strength decays significantly along the axial direction due to turbulence evolution. Turbulent kinetic energy (TKE) distributions were analyzed on the 20%, 50%, and 80% Span planes, showing that high-energy regions are mainly concentrated in the trailing-edge jet–wake region and at the high span plane location, which are also key regions of flow instability. Quantitative analysis of the pressure-pulsation amplitudes in the impeller passage and on the blade surface at fBPF, 2fBPF, and 2.8fBPF frequencies revealed the modulation effects of high-order harmonics under different flow conditions. These findings not only deepen the understanding of vortex–pressure coupling mechanisms in pumps but also provide theoretical support for the geometric optimization of the impeller.