In the present study, a Reynolds-Averaged Navier-Stokes (RANS) method is employed in conjunction with a Chimera domain decomposition approach to provide accurate resolution of coupled ship and propeller flows. In the Chimera RANS method, body-fitted numerical grids are generated around each propeller blade to provide accurate resolution of the turbulent boundary layer, wake, and blade tip vortices. The propeller grid blocks are completely embedded in the ship stern region and allowed to rotate with respect to the ship grid. This enables us to capture the propeller-hull interactions without tedious grid reconstruction at every time step. Calculations have been performed for the DTRC 4118 propeller under both the design and off-design conditions to illustrate the capability of the chimera moving grid approach.
The potential flow methods based on the assumption of inviscid fluid and irrotational motion are widely used in propeller flow analysis (Kerwin and Lee, 1978; Greeley and Kerwin, 1982). However, some off-design propeller flow phenomena are dominated by viscous effects and cannot be accurately predicted by the potential flow methods. Off-design conditions include all four quadrants as defined by the ship velocity Vs and the propeller angular velocity ω. The four modes of propeller operation are defined as ahead or forward (+Vs, +ω), backing or astern (−Vs, −ω), crash-ahead or reverse backing (−Vs, +ω) and crash-back or crash-astern (+Vs, −ω). During crash-astern and crash-ahead operations, the reversal of propeller rotation creates a relatively large angle of attack, causing the flow to separate at the leading edge of the blade. The water tunnel measurements performed by Jiang et al. (1997) demonstrated that the flow is unsteady, even when the propeller is operated in the steady crash-astern condition.
Jiang et al. (1991) extended the inviscid-flow propeller design methods for the simulation of backing and crash-astern conditions.
