Spatial-temporal evolution and pressure fluctuation characteristics of the combined submerged vortex in a closed pump sump

Abstract

Following the retrofit of the pump sump, there is a high risk of inducing the Combined Submerged Vortex (CSV), which consists of the roof-attached vortex (RAV) and floor-attached vortex (FAV). This vortex formation can lead to irregular pressure fluctuations, adversely affecting the unit's performance and compromising the stability of energy conversion. This study aims to investigate the spatiotemporal evolution of the CSV and its associated pressure fluctuation characteristics in a closed pump sump. High-speed visualization and pressure fluctuation tests are conducted on a transparent closed-loop test rig. The findings demonstrate that the spatiotemporal evolution of the CSV can be divided into three stages: developing, competing, and collapsing. The competing stage, in particular, has a significant impact on the FAV. During the CSV period, the dominant low frequencies induced by the RAV and FAV are 0.24 and 0.13 Hz, respectively, with the FAV exhibiting higher intensity than the RAV. The regions of high coherence between the RAV and FAV are primarily concentrated within the low-frequency range of 0.25–2 Hz, and the signals exhibit multiple phase differences. Furthermore, a vortex identification criterion for a closed sump is proposed based on Continuous Wavelet Transform.