Numerical Study on the Unsteady Hydrodynamic Performance of a Waterjet Impeller

Gong, J.; Guo, C.-Y.; Wu, T.-C., and Song, K.-W., 2018. Numerical study on the unsteady hydrodynamic performance of a waterjet impeller. Numerical simulations of the internal flow field of a waterjet-propelled ship have been performed to evaluate the unsteady hydrodynamic performance of the impeller. Hydrodynamic performance of the impeller provides a great influence on ships with waterjet propulsion when sailing in coastal environments and zones farther out to sea. Nonuniform axial velocity entering the channel causes unsteady loading of the impeller blades, resulting in noise and vibration, and it increases the risk of impeller cavitation. The hull modeled in this study is the INSEAN 2340, fitted with a waterjet-propulsion system. Numerical simulations are for unsteady, multiphase flow and include free-surface effects. Meshing of the hull and waterjet, selection of the turbulence model, and calculation conditions set to satisfy all research objectives are discussed. The simulation results showed that the internal flow field featured with gas–liquid mixed flow and reflow phenomena in the channel. A varied pressure distributed over the blade surface, and the surface pressure pulsation was considered to be more intensely close to the channel during a cycle. It is found that the thrust and torque coefficients of the impeller were periodically fluctuating within one period. The average fluctuation range of thrust coefficient is −4.07%∼3.39% to its mean value, which demonstrated the unsteady quantitatively. Additionally, thrust deduction existed when the impeller rotated to a particular position of a single blade, and the loads on the impeller blade surface tended toward stabilization as the rotating speed increased.