Multiscale formation mechanism and instability characteristic of the submerged vortices caused by a closed pump intake

Abstract

The intake system serves as a crucial inlet structure for tidal pumping stations along the coastal regions. However, the various types of submerged vortices caused by the closed intake disrupt the energy-conversion stability, limiting the efficient and safe operation of the units. Especially when the multiple vortices are mixed enter the pump, the pump's energy consumption increases, and the hydraulic stability of the intake further decreases. This study used the high-precision simulation method to elucidate that the anisotropic turbulent structure around the roof-attached vortex (RAV) and the Reynolds shear stress are the critical factors for initiating small-scale RAV. The vertical and its enstrophy transport equation were used to explain that the vortex stretching term is the primary source of inducing the vertical vorticity evolution of RAV and floor-attached vortex (FAV). The tilting term provides a power source for vortex wandering. Based on the high-speed visualization experiment, the instability characteristics analysis of the vortices showed that the root of RAV dissipation was the existence of a critical stagnation point, SRAV, and the dissipation form exhibited “bubble-like fragmentation.” The unstable dissipation of the FAV does not have a vital stagnation point, and the dissipation form manifests as “vortex filament dissipation.” The results have important academic value and theoretical guidance significance for ensuring the safe and efficient operation of the tidal units.