Joseph Katz

Department of Mechanical Engineering

Whiting School of Engineering

John Hopkins University

March 24, 2010

1:10 - 2:00 PM

Room 1235 Howe Hall

Application of Digital Holography to Characterize Buffer Layer Structures Generating Extreme Wall Stress Events in a Turbulent Boundary Layer

The presentation introduces several applications of digital holography as a means of resolving complex flows and particle tracking. A detailed discussion focuses on simultaneous measurements of three dimensional velocity distributions and wall stresses in the inner part of a smooth wall turbulent boundary layer. Conditional sampling based on local shear stress maxima and minima reveals two types of dominant buffer layer structures. The first develops as spanwise vorticity lifts abruptly from the wall and stretched to forms a counter rotating vortex pair. A wall-stress minimum forms under the point of initial lifting, and two stress maxima develop 35 wall units downstream due to vortex-induced entrainment. The second structure is a single, slightly inclined streamwise vortex. It generates a strong elongated stress maximum on one side, and a weak minimum on the other. The seminar will conclude with sample applications of high-speed cinematic digital holography, including breakup and turbulent diffusion of crude oil droplets, as well as swimming behavior and interactions among marine organisms.

Bio: Dr. Joseph Katz is the William F. Ward Sr. Distinguished Professor in the Department of Mechanical Engineering at The Johns Hopkins University. He received his BS degree from Tel Aviv University and MS and PhD from Caltech, all in Mechanical Engineering. After a few years at Purdue University, he joined the Johns Hopkins University in 1988.

Dr. Katz is a Fellow of ASME, and has been the Technical Editor of the Journal of Fluids Engineering since 2000. He is also a Fellow of the American Physical Society.  He has advised numerous graduate students and post-docs, most of whom currently hold academic, industrial and government research positions around the world. He has received several awards, including the 2004 ASME Fluids Engineering Award.

His research focuses on experimental fluid mechanics and development of advanced diagnostics techniques for laboratory and field applications. His groups have been involved in characterization of turbulent single and multiphase flows, such as: (i) rapidly strained turbulence, (ii) bubble and droplet dynamics including cavitation in attached and free shear flows, (iii) flow structure and turbulence within turbomachines, such as wake-wake and wake-blade interaction, (iv) the structure of ship bow waves, (v) turbulence in the bottom boundary layer of the coastal ocean, and (vi) flow structure and turbulence associated with canopy flows. He has also been involved in measurements of swimming behavior of plankton both in the laboratory and in the ocean.

In terms of techniques, his group has been involved in development and applications of Particle Image Velocimetry (PIV) and its derivatives in complex environments, both in the laboratory and in the ocean and cornfields.  This has also included Holographic PIV and particle tracking, including digital holography, in laboratory and field studies. Results of Dr. Katz’ research work have been described in about 100 journal papers and 150 conference papers. His research has been funded by ONR, NSF, AFOSR, DOE, and NOAA.