Interaction of a vortex pair with a free surface : measurements and computations

Abstract

An investigation of the interaction of two-counter-rotating vortices with a free surface has been undertaken. Experiments were carried out in two water basins and in a long towing tank through the use of measurements, flow visualization, and an infrared camera. The results have shown that all types of vortex pairs over a wide range of Froude Numbers give rise to three-dimensional surface disturbances, known as scars and striations. The striations are a consequence of the short wavelength instability inherent to the vortex pair itself. The scars are transported outward by the vortex pair and are comprised of a constellation of coherent vortical structures (whirls). The experiments have provided sufficient understanding of the physics of the phenomenon and led to the development of a numerical model based on vortex dynamics. This model proved to be capable of explaining the physical processes involved in the evolution of the three-dimensional footprints of the vortex pair.