Scanning large geometries for use in computational fluid dynamic analysis

The accuracy of Computational Fluid Dynamics (CFD) is highly dependent upon the geometrical accuracy of the assembled model. Non-contact laser scanning can be used to acquire detailed geometrical data, from which highly accurate models can be created. In this paper the methods and issues associated with the use of such a technique, from the initial capture of data through to a final CFD analysis, are presented. A non-contact laser scanner was used to capture the geometry of an Olympic class Yngling Keelboat. Prevention of accidental movement during the scanning process and surface reflection characteristics required consideration. Scanning was performed in stages due to the size of the Yngling. Datum techniques were therefore required to enable reassembly of the separate scans into a complete model. The captured data was cleaned and surfaced and used to generate an accurate NURBS CAD model. A hydrodynamic CFD study of the Yngling, investigating the influence of leeway angle upon the lift/drag ration of the keel, was then performed. The maximum life/drag was obtained at a leeway angle of 5°. The lift generated by the keel increased as leeway was increased. However the drag on the appendage attributable to vortex shedding also increased. This had a detrimental effect upon the life/drag ration for angles of leeway greater than 5°.