Numerical Analysis of Two-Phase Flow in the Cavitation Process of a Waterjet Propulsion Pump System

Jiao Jiao,Wang Wang,Cheng Cheng,Xu Xu

doi:10.3390/pr7100690

Abstract

The waterjet propulsion system has been widely used in the military and civil fields because of its advantages of in terms of high efficiency and energy savings. In order to study the three-dimensional cavitation flow in the waterjet propulsion pump, the cavitation process of the waterjet propulsion pump was simulated numerically using the Zwart–Gerber–Belamri cavitation model and the RNG (Renormalization Group) k-ε model. The simulation results of cavitation on the waterjet propulsion pump and pump system show that, in the initial stage of cavitation, vapors first collect on the leading edge of the suction surface of the blade near the rim of the impeller. As the total pressure at the impeller inlet decreases, the cavitation region expands toward the trailing edge and the vapor fraction volume gradually increases. In order to simulate the cavitation state of the waterjet propulsion pump under the actual working conditions, a numerical simulation of the entire waterjet propulsion pump system with inlet passage was carried out. After assembling the inlet passage, the flow pattern at the impeller inlet becomes uneven, leading to irregular changes in the cavitation region of the impeller. The potential danger regions of cavitation are the lip of inlet passage and the upper and lower connecting curved section of the inlet passage. The performance of waterjet propulsion pump system changes greatly when the net positive suction head available (NPSHa) value of the pump reaches the critical value.

Highlights

Waterjet propulsion is largely used in the military and civil fields because of its simple transmission mechanism, low noise, and good maneuverability [1,2,3]
The net positive suction head of the waterjet propulsion system is obviously lower than the NPSHr (Net Positive Suction Head Required) of the pump at this speed, and the propulsion pump is prone to cavitation
The net positive suction head-available pump is the reference static pressure, which is expressed as the pump inlet pressure in this study; whereinlet (NPSHa) refers to the excess energy of the liquid at the pump inlet that exceeds the vaporization is theatvapor pressure; and U is the reference velocity, which is expressed as the inlet tip speed

Summary

Introduction

Waterjet propulsion is largely used in the military and civil fields because of its simple transmission mechanism, low noise, and good maneuverability [1,2,3]. While compared to propeller propulsion waterjet propulsion can utilize the inflow stamping to increase the anti-cavitation capability at high speeds, cavitation problems may arise under some special conditions such as “low ship speed and high rotating speed” [4,5]. This special working condition usually occurs in the process of ship acceleration or turning. At this time, the net positive suction head of the waterjet propulsion system is obviously lower than the NPSHr (Net Positive Suction Head Required) of the pump at this speed, and the propulsion pump is prone to cavitation. It will cause noise and vibration in the pump [6,7,8,9,10]

Methods

Results

Conclusion