Computational fluid dynamic investigation of hull-waterjet flow interaction

Abstract

A comparison of reliable experimental data with the prediction of a Computational Fluid Dynamics (CFD) package for the flow over and through the upstream hull and inlet duct of a water-jet geometry has been carried out. The flow solver algorithm used is based on the incompressible, three-dimensional Reynolds averaged Navier-Stokes equations for turbulent flow with a k-ε turbulence model. A detailed series of wind tunnel tests of a representative water-jet geometry have been carried out for a range of duct exit velocity to ship speed ratios. Detailed surface pressure measurements and velocity profiles within the duct were obtained. A multi-block grid generator was used to produce a computational mesh of the water-jet inlet duct and wind tunnel working section which represented the ship hull. Solutions were obtained for comparable conditions to those tested. It was found that both the surface pressure variations and velocity profiles along and around the duct were well predicted as was the influence of operating condition. The differences found were principally attributed to the lack of grid resolution for the boundary layers and in areas of rapidly changing curvature. The CFD working section was then changed for a flat plate surrounding the duct inlet. This model was used to study the influence of pitch and yaw on the pressure distributions along the duct and velocities at the impeller face place. The results were promising and the predicted trends were as expected. In addition, modelling the influence of a simple hull shape on the flow through the water-jet inlet has been investigated. The ability of the flow solver to obtain reasonably accurate solutions was demonstrated, allowing predictions to be made of the total force distribution on both the hull surface in the vicinity of the duct and on the inlet duct itself. It is concluded that it is possible to model the water-jet system at present and obtain practical design information. However, significant improvements are still required to the methods by which complex three-dimensional shapes are defined in order to allow rapid parametric studies.

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ORCID for S.R. Turnock: orcid.org/0000-0001-6288-0400

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