Numerical investigation on vortex characteristics inside a jet pump under low entrainment ratio conditions

Abstract

The entrainment ratio is a crucial parameter affecting jet pump performance and efficiency. A low entrainment ratio induces chaotic flow patterns within the pump, leading to reduced efficiency. Understanding these chaotic flow patterns is essential for optimizing jet pump design and operation. In this study, the mesh was optimized for low entrainment ratio conditions, and the internal flow field of the jet pump was simulated. The results revealed the presence of multiple vortices between the shear layer and the pump wall under low entrainment ratio conditions. These vortices were classified into primary and secondary vortices based on their size. Secondary vortices have a negligible effect on pump performance, while primary vortices facilitate energy transfer by supporting the shear layer when it cannot fully extend to the wall. However, primary vortices also cause irreversible energy losses and elevate frictional resistance along the inner wall, leading to a decrease in efficiency. Using a working fluid with a lower viscosity but similar density results in a minor efficiency improvement. Strategies such as increasing the entrainment ratio, optimizing the area ratio, adjusting the nozzle exit position, and using a converging throat effectively reduced the primary vortex size and improved jet pump efficiency.