Transient numerical simulations for hydrodynamic derivatives predictions of an axisymmetric submersible vehicle

In this study, a method for obtaining of hydrodynamic derivatives by numerically replicating the Planar Motion Mechanism (PMM) tests of an axisymmetric submersible model is demonstrated. The numerical simulations of PMM tests are regarded as transient due to the movement of the model in the discretized computational domain thus causing mesh deformation. To accommodate the sway and yaw oscillation motions of the model, the entire computational domain is divided into three zones namely rotating, inner and outer zone. Multi-block structured grid is generated with finer resolution in the proximity of the model to capture the boundary-layer flows. Non-conformal fluid interfaces are used to connect the three zones. Commercial CFD Solver FLUENT is used to simulate the flow characteristics while the dynamic mesh capability included in the software is applied to handle the mesh deformation during the movement of the model. In order to verify the CFD method, 6:1 prolate spheroid is used as it can be idealized as an axisymmetric submersible model. The CFD results of added mass derivatives of the model show very close agreement when compared with the theoretical values. The present study is an attempt towards developing an economical CFD method for evaluating the hydrodynamic derivatives of submersible platforms such as submarines, torpedoes and autonomous underwater vehicles during early design stages.