Numerical Simulation of the Complex Flow through Rim Driven Thrusters Seminar

A rim driven thruster is an electromagnetic marine propulsion device that uses a motor in its casing to drive a propeller by its rim.  There are many interacting flow features that make up the flow field of a rim driven thruster which pose challenges when it comes to simulating the device.  The purpose of this work is to develop a computational fluid dynamics process that accurately simulates features including vortex generation and behaviour, radial pumping and rotor-stator interaction.  Computational costs should be minimised to enable quick calculation of an objective function, typically thrust or propulsive efficiency, in a design optimisation study.  Implementation within a design optimisation study requires repeatable and robust numerical methods in both mesh generation and solution.

Mesh generation was performed using snappyHexMesh, a meshing utility in the open source package OpenFOAM, and a thorough mesh verification procedure was conducted.  Validation of the solution of a standard series Wageningen B4-70 propeller, as a baseline case with good experimental data from MARIN, using the Reynolds-Averaged Navier-Stokes solver MRFSimpleFoam (also part of OpenFOAM) was performed and shows good agreement with experimental data.  The Re-Normalisation Group (RNG) k-epsilon and k-omega Shear Stress Transport (SST) turbulence models, as the most widely used in literature are compared and the k-omega SST model is found to be the most robust due to its better handling of separation that occurs at low propeller advance ratios.  Results show a great sensitivity to computational domain size and, for the rim driven thruster, show that MRFSimpleFoam does not capture the rotor-stator interaction sufficiently.  An alternative unsteady solution method is being developed to investigate the rotor-stator interaction fully and preliminary results  from this method are presented.