Development of a modified body force method for modelling azimuth thrusters in CFD-based manoeuvring simulations

Ship manoeuvring simulations based on Computational Fluid Dynamics (CFD) are advanced tools for evaluating vessel performance, allowing for detailed analysis of various manoeuvres while considering viscous and environmental effects. However, this approach is often associated with high computational cost, due to the fine temporal discretisation required to capture propeller motion. To alleviate this, propellers are commonly replaced with a Virtual Disk (VD), which contains volumetric source terms that replicate the flow field generated by the propeller. However, conventional VD methods typically overlook side forces and do not account for the tangential distribution of nozzle forces, limiting their ability to replace both the propeller and nozzle. This study aims to address these limitations and expand the scope of the conventional VD methodology to include azimuth thrusters. The primary objective is to provide a method for determining thruster-specific momentum sources and their distribution based on systematic Reynolds-averaged Navier-Stokes (RANS) CFD simulations with varying flow conditions. Source terms derived from these simulations are incorporated in an existing VD framework within a commercial CFD solver to create a Modified Virtual Disk (MVD). Comparisons with initial simulations show that the proposed method effectively reproduces the resulting forces and flow fields, while significantly reducing the computational effort.