Research on cavitation characteristics of water-jet pumps with different blade tip clearances based on entropy production theory

Abstract

Water-jet pumps are widely used in ship and other power fields. An axial-flow water-jet pump is studied with different size of tip clearance, and the cavitation characteristics are studied based on the theory of entropy production. Modified SST with curvature correction and modified Zwart cavitation model based on vortex identification are adopted, and the numerical calculation method is verified by reference experiments of a model pump. Under normal operating conditions, the results show that when the size of the tip clearance varies from 1.6‰ to 7.9‰ of the impeller diameter, efficiency takes a linear decrease accordingly, and the total entropy production increases linearly. At the same time, the main energy dissipation mode changes from wall dissipation to turbulent dissipation. Under severe cavitation conditions the total entropy production adds 30%. The water-jet pump shows that the entropy production in the impeller section is the highest, which accounts for 40%-50% and is closely related to the vortex and cavitation flow field in the tip clearance of the impeller. The tip leakage vortex region causes cavitation, but significant energy dissipation occurs at the outer edge of leakage vortex and on the nearby wall area, while the attached cavitation on the blade surface is the main source of turbulent dissipation.