A novel method for two-dimensional physical modelling of a vessel's rudder wake using flowing soap films

Flowing soap films have been used in recent years as an apparatus to study natural phenomena encountered within fluid dynamics, such as the movement of flexible bodies within a flow field [1]. The apparatus consists of a water/soap solution which is suspended between two threads and allowed to flow from a raised position. This creates a thin sheet of flowing liquid into which static or moving bodies can be placed. This thin film may be considered to be two dimensional as it is typically 105 – 106 wider than it is thick [2]. The water/soap solution results in a thin water layer covered by a soap surfactant. When photographed under a monochromatic light source, the movement of the surfactant on the film can be clearly visualised. The primary aim of the research was to investigate the applicability of flowing soap films to the field of Naval Architecture for use as a tool for the qualitative assessment of hullforms. The following questions were investigated: - Can the wake from a ship be adequately modelled using flowing soap films? - How does twin rudder positioning/spacing affect this modelled wake? - Can the wires supporting the flowing soap film be used to model a system boundary, such as the sea surface or bottom? - Can the forces acting on bodies inserted into the soap flow be readily measured?