Numerical hydraulic efficiency analysis of waterjet propulsion

Abstract

Insufficient understanding of large deviations between theoretical efficiency and measured efficiency is a major problem encountered in the water-jet propulsion design and application. Therefore, reason analysis of the poor efficiency is necessary. In this paper, CFD was directly adopted in the hydraulic loss distribution of water-jet propulsion. At reliable conditions, nearly 50% hydraulic losses took places in the water-jet pump, and the intake duct was the second. Then, the normalized helicity analysis of the intake duct revealed that the formation and dissipation of an instability secondary vortex was the main reason for hydraulic losses. In the next step, complete pump performances with the uniform and non-uniform inflow were acquired. As a result the non-uniform inflow of water-jet pump was the primary reason for the poor efficiency. Eventually, comparison and discussion were carried out to investigate the correlation between the water-jet pump performance and velocity components of the non-uniform inflow. According to the non-uniform inflow, the inlet pre-swirl reduced the angle of attack and impaired the work capacity, the violent change of the inlet meridional velocity and circulation resulted in the block and secondary flow on the blade shroud, the increment of radial velocity broke the circumference independence hypothesis.