Plenary Lecture

Scalar Dispersion and Turbulent Mixing in Grid Turbulence, More Complex Flows, and on Geophysical Scales

Professor Paul E. Dimotakis
John K. Northrop Professor of Aeronautics and Professor of Applied Physics
California Institute of Technology
Pasadena, CA 91125
Tel/Fax: USA (626) 395-4456/-4447
USA
E-mail: dimotakis@caltech.edu

and

Chief Technologist
Jet Propulsion Laboratory, M/S 180-601
4800 Oak Grove Drive
Pasadena, CA 91109-8099
Tel/Fax: (818) 393-7600/-1554
USA
E-mail: Paul.E.Dimotakis@jpl.nasa.gov

Abstract: Scalar dispersion and mixing in turbulent flows are important phenomena in a variety of contexts. These range from internal combustion in general and chemical air-breathing propulsion, to local atmospheric pollution and dispersion, to Earth system transport and climate modeling. The first part of the discussion will focus on the structure of the scalar dispersion field originating from a continuous release point in moderate Reynolds number flow in grid turbulence. Using laser-induced fluorescence techniques, laser-volume scanning, a custom-designed fast-readout CCD focal plane array, and high-speed digital-imaging/-acquisition/-storage techniques, the instantaneous three-dimensional structure of a passive scalar in flow in water will be presented. The instantaneous three-dimensional topology of scalar structures and their persistence in the self-similar grid-turbulence regime where the present three-dimensional scalar-field measurements were conducted will also be discussed. The second part will focus on scalar transport and mixing in a complex recirculating flow, in which molecular mixing is quantitatively measured in chemically reacting flows using hydrogen and fluorine as reactants in the mixing-limited (high Damkohler number) chemical reaction regime. Finally, recent space observations of the concentration of carbon dioxide at a pressure height of 500 mbar in the atmosphere will be presented and discussed, along with their implications to global transport and dispersion in the northern and southern hemispheres.

Brief Biography of the speaker:
Paul E. Dimotakis received his degrees at the California Institute of Technology (Physics, Nuclear Engineering 1969, and Ph.D. in Applied Physics). He stayed on at Caltech where he is presently the John K. Northrop Professor of Aeronautics and Professor of Applied Physics. Starting in January 2006, he also serves as the Jet Propulsion Laboratory (JPL) Chief Technologist.

Following work on liquid helium and superfluidity, his research focused on investigations of turbulent-flow phenomena, with an emphasis on turbulent transport and mixing in chemically reacting as well as non-reacting flows and combustion, in both subsonic and supersonic flows. He and his co-workers have developed several experimental facilities, diagnostic methods, introduced advances in signal processing, high-speed digital temporal- and image-data acquisition techniques, high-speed CCD imager design, and image-data processing. His research has also included work on active control of separated flows, studies of cavitation, hydrodynamic stability and gasdynamic simulations, image-correlation techniques for velocity-field (optical-flow) measurement, multi-dimensional measurements, aerooptics effects as well as work on adaptive optics. In work outside Caltech as a consultant, he has participated in the development of pilotless drones, high-power chemical lasers, the stealth fighter, the development of the Space Shuttle aerodynamics, assisted in the internal aerodynamics of sealed computer (Winchester) disks, helped with the fluid mechanics design of the "Leap-Frog fountain" at Disney's Epcot Center in Florida, and participated in experiments in the Lawrence Livermore's laser facilities. Also a sailor, he was a member of the AMERICA3 sail-design team in their successful defense of the Americas Cup in 1992. Paul Dimotakis has served as Associate Editor for the J. Fluid Mechanics, is presently a Fellow of the American Physical Society, an Associate Fellow of the AIAA, and was recently elected Fellow of the AAAS.

He has served on National Academy of Science panels on Inertial Confinement Fusion and High-Energy Density Physics, and has led studies on space-launch options, space propulsion, hypersonics, high-speed ships, thermal management of high-energy lasers, fossil-fuel use by the Department of Defense, long-endurance UAVs, and on other topics.