Numerical study on self-propulsion of a waterjet propelled trimaran

The hydrodynamics of the waterjet propelled ships represents a challenging problem due to the complexity of the waterjet system itself and the waterjet/hull interaction. In this paper, the self-propulsion computations of a trimaran were performed by solving the unsteady RANS equations. The waterjet was simulated directly with multi-reference frame model to improve the precision of the numerical simulations. Mesh independence studies of the hull and waterjet were carried out individually. Numerical simulations with/without the waterjet were performed in a speed range of 0.196 < Fr < 0.707. Comparisons between numerical predictions and experimental data showed the numerical method could accurately predict the self-propulsion performance. A numerical tool was developed to obtain the capture area based on tracking the streamlines upstream, which was practical and greatly simplified the post-processing. According to the ITTC procedures and guidelines, the overall efficiency and its components were analyzed in detail. The results showed that the resistance increment was always positive while the waterjet thrust deduction fraction was negative. The overall efficiency of the waterjet was mainly affected by the ideal jet efficiency and the pump efficiency. The analysis of the waterjet powering characteristics can better understand the energy conversion and the interaction between the ship hull and waterjet.