Research on streamtube and capture area of waterjet propulsion system

It is an important content to determinate accurately momentum flux and energy flux on capture area of a waterjet propulsion system for powering characteristics prediction. Besides the mass flow rate through waterjet and the velocity profile underside of hull bottom,the shape and scale of capture area are essential to calculate the momentum flux and energy flux. But some disagreement still exists now on determination of capture area and its effects on prediction accuracy of power characteristics. In this paper the flow around a waterjet system is simulated by means of a CFD code to investigate this issue. The internal flow suctioned by waterjet and the external flow are distinguished by solving a user-defined-scalar function. Then the streamtube and capture area at various inlet velocity ratios(IVR)can be achieved accordingly. Calculation results indicates that:① The width of capture area approximately equals to twice of inflow duct diameter,varying hardly along with increasing IVR; ② The shape of capture area appears semi-elliptic at general range of IVR,transiting from plumy to plat with IVR decreasing,and falling inside at middle part at very low IVR; ③ The shape of capture area keeps invariable in different longitudinal positions along hull.