Abstract: The inlet duct grids and their spaces between them make significant influence on the flow in waterjet inlet duct and propulsion performance. Three flow fields in the same inlet duct with no grid, three grids and eight grids are calculated by computational fluid dynamics method, and three ship speeds according with inlet duct efficiency, mass flow rate, and non-uniformity of duct outlet are received. The numerical results are compared and indicated that at the same rotation rate of main engine the installation of inlet grids reduce the inlet efficiency, non-uniformity of duct outlet, the ship speed, mass flow rate, and propulsion efficiency. Reducing grid spaces brings greater reduction of these parameters. The physics essences of the changes of parameters are analyzed from mechanism point. The study indicates that inlet grids can reduce the duct flow performance and also reduce waterjet propulsion performance.

Key words: Duct, Grids, Numerical simulation, Propulsion performance, Ship, Waterjet