Aero-hydrodynamic behaviour of waterborne WIGcraft : an experimental,numerical modelling and simulation study

Abstract

This thesis makes an in-depth investigation on the aerodynamic, hydrodynamic and coupled aero-hydrodynamic behaviors of the water-borne Wing-in-ground effect marine vehicle (WIGcraft) via the development of semi-empirical and numerical tools to evaluate the behaviour of a waterborne WIGcraft model. Semi-empirical models and three potential flow-based numerical simulation models namely, hydrodynamic model for single-/multi-hull planing Outrigger model, ground effect aerohydrodynamic model for air borne WIGcraft model, and aero-hydrodynamic model for water borne WIGcraft model were developed to investigate the effects associated with coupling wings to a planing boat. The hydrodynamic model was developed by extending the 2.5D theory to non-similar planing hulls. The ground effect aerohydrodynamic models for air borne and water borne WIGcraft were developed by implementing a numerical slender wing/body theory in a manner analogous to the 2.5D theory to account for the strong nonlinear 3D flows and free surface deformation within the small gap of the WIG-craft moving at constant speed with its wings near undisturbed water surface. As an alternative to the application of image methods commonly used for planar ground effect studies of wings and airfoils, momentum conservation and flow continuity principles were innovatively enforced at the airwater interface through an iterative algorithm. The aero-hydrodynamic models essentially combine the hydrodynamic model and ground effect aerodynamic model at the air-water interface. The three numerical models were validated by means of numerical simulation results obtained from Vortex Lattice Method based Autowing code, as well as with results from captive model experimental tests carried out for an outrigger ship and WIGcraft models. The result from a linear superposition of aerodynamic and hydrodynamic forces and that of a non-linear coupling of the hydrodynamic and aerodynamic models suggest the existence of non-linearities that have a non-negligible effect on the waterborne WIGcraft. This study shows the significance of ground effect, hull generated spray and non-linear coupling effects on the WIGcraft, the correct location, aerodynamics, geometric and structural design of the wings near free surface water, as well as the hull design and stability of a moving water borne WIGcraft.