Large Eddy Simulation of submerged vortices in a pump sump

Abstract

Unsteady submerged vortices in the test pump sump with 100 mm height and 100 mm diameter of the inlet pipe are investigated by performing large eddy simulations （LES）. Width of the pump sump is 300 mm and the inlet velocity is 0.37 m/s. Computational grids with 0.255 mm horizontal resolution resolve turbulent boundary layer on the bottom and side wall of the pump sump. Unsteady flows with different conditions for boundary layer on the wall of the pump sump were computed to investigate the relationship between the boundary layer and vortices generation. In these flow computations, we found that the origins of the submerged vortices are shear of the boundary layer. However we underpredicted the pressure drop of a vortex core because the grid resolution is not enough to present vortex cores. In order to take finer grid resolution, we used a simplified computational model where the computational domain is localized to vortex core. Its horizontal grid resolution is 0.03 mm. A pressure drop of a vortex core computed by the simplified computational model is 40% for the atmospheric pressure, while one computed by LES for the pump sump model is 5%.