Turbulence on a Free Surface

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

This research project deals with fluid dynamics. It is co-funded between the Condensed Matter Physics Program In the Division of Materials Research and the Fluid Dynamics and Hydraulics Program in the Division of Chemical and Transport Systems. It is a study of turbulence at the free surface of a closed body of fluid. The fluid motion or turbulence is detected by observing the in plane, horizontal velocity components of small particles entrained at the air/water interface. A large laser illuminates the surface particles, which are tracked with a fast camera. At points at and below the surface, the flow is incompressible; this implies that the surface velocity is, by contrast, compressible. Because energy and vorticity can be freely exchanged with the fluid below, Kolmogorov-type dimensional arguments are not available, so one must turn to computer simulations to model the motion. One phenomenon of interest is the tendency of particles to cluster rather than disperse. The observations are relevant to practical issues such as dispersal of pollutants at the surface of a turbulent sea and the growth rate of biological organisms at an air/water interface. The educational component is focused entirely on undergraduate students. The experimental techniques, which are computer intensive, provide an excellent training ground for physics majors, engineers, and those interested in pattern recognition issues. They will be prepared for a range of careers in academe, industry and government This fluid dynamics turbulence research project is co-funded between the Condensed Matter Physics Program In the Division of Materials Research and the Fluid Dynamics and Hydraulics Program in the Division of Chemical and Transport Systems. Turbulence invariably appears when objects move rapidly through the air or the sea. An understanding of the complex phenomenon of turbulence is necessary in order to improve weather prediction and to better cope with natural and man-made disasters such as storms and pollution spills. The focus here is on the motion of small particles that float on a turbulent body of water. These 'floaters' may be thought of as a surrogate for the motion of buoys, ships, or floating pollutants. Turbulence at the surface has the unusual effect of causing the floaters to clump together, whereas they are dispersed elsewhere in the bulk sea or the air. This study is one of the first to be carried out under laboratory-controlled conditions. The educational component is focused entirely on undergraduate students. The research utilizes cutting-edge technology for tracking the particle motion (high-speed cameras and powerful new solid-state lasers) and provides an excellent training ground for students majoring in fundamental science or engineering.