Concentrated separation vortex induced by non-uniform suction flow and its role in performance breakdown of a water-jet pump

Puyu Cao,Gang Yin,Guidong Li,Zhang Xiang,Yang Wang

doi:10.1177/1687814017703349

Abstract

Many water-jet pumps have a suction velocity profile, which is non-uniform and unfavorable for the pump performance. This article applies the numerical method to investigate the generation mechanism of performance breakdown in a water-jet pump under non-uniform suction flow. The mechanism dictating flow details in the impeller, including the inlet velocity, flow angle, and boundary layer separation, is systematically studied at the design point. Observations show that the nature of non-uniform inflow is a circumferential distortion upstream of the impeller shroud, which is proved to be a stationary stall cell associated with a velocity deficit near the top sector. Meanwhile, a detailed analysis allows the identification of flow separation and vortex in the impeller. The circumferential distortion gives rise to a high incidence, the occurrence of suction surface separation, and the consequent formation of a concentrated separation vortex near the blade shroud. Furthermore, particular attentions are devoted...

Highlights

The water-jet propulsion system is widely used to thrust high-speed marine vessels due to its relatively high propulsive efficiency, good maneuverability, and less vibration over conventional propellers.[1]
High-velocity particles near the bottom are acted upon by a larger centrifugal force than the slow particles near the top do.[12]. These radii and bending angle generate a transverse pressure gradient perpendicular to the main flow direction between the bottom and top. As these asymmetric distributions are imposed on the water-jet pump, it is considered that different sectors or channels of the impeller operate at different flow conditions, which implies their working on different off-design points of the Q–H curve
Because the cavitation and stall cells generally disappear at the design point, and exert slight influences on the the head breakdown with respect to the nonuniform suction flow

Summary

Introduction

The water-jet propulsion system is widely used to thrust high-speed marine vessels due to its relatively high propulsive efficiency, good maneuverability, and less vibration over conventional propellers.[1]. Hu and Zangeneh[8] stated that the non-uniform inflow had an insignificant effect on the torque of a water-jet pump His calculation domain was a signal impeller, and the inlet boundary condition was set as a pitch-averaged velocity. The computation zone includes six individual parts to calculate pump performance under non-uniform inflow, namely, the impeller (rotor), guide vane (stator), discharge nozzle, straight pipe, intake duct, and an upstream region. The steady-state simulations of the complete water-jet propulsion system were carried out and the pump performances under the non-uniform inflow were obtained. The average total pressure was imposed as an inlet boundary condition of the single pump, and the outlet boundary condition was set as the mass flow rate in accordance with the numerical result of the propulsion system. The pump head was calculated between the same sections

Experimental setup

Discussion

Conclusion

Findings

London