Energy Balance Approach for Studying Waterjet-Hull Interaction Effects

Paper in proceeding, 2023

Waterjet-hull interaction effects are usually studied by analyzing hull attitude in the presence of a waterjet unit as well as the counteracting resistance and thrust forces. Since the waterjet unit is integrated with a hull, net thrust cannot be accurately measured. Instead, it is suggested to use an alternative measurable thrust, gross thrust, to study the interaction effects. Gross thrust is the momentum flux change through the waterjet unit and is calculated by obtaining axial velocity distribution at the inlet to the waterjet unit and the nozzle outlet. However, this approach does not provide detailed information about system power consumption. In this paper, a more comprehensive method is suggested in addition to the momentum flux approach. The method is based on the investigation of energy flux through the waterjet system. This approach not only enables us to qualitatively describe the flow but also makes it possible to quantify different energy flux components and understand the energy loss mechanisms within a waterjet system. The required flow quantities for this analysis are obtained from a Reynolds-Averaged Navier-Stokes approach together with a Volume-of-Fluid method for capturing the free surface. The transport equation for energy is also solved for obtaining the viscous losses in the form of internal energy increase in the flow. The sum of mechanical and thermal energy components computed by analyzing energy flux through the waterjet system deviates less than 0.5% from the pump-delivered power. This confirms the capability of the proposed method for capturing the decomposition of different energy components in the flow. Further analysis of the decomposition of energy flux through the waterjet system is carried out to identify the loss components in the flow.