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Weekly Seminar: Spring 2018

Speaker: Prof. William K. George (Imperial College of London, UK)
Title:
"Reconsidering K41: The Kolmogorov Theory for Small Scale Turbulence"
Hosted By: Joseph Katz (ME)

Date: Friday, February 2, 2018
Time: 3:00 p.m. (New Time)
Location: Gilman Hall # 132


Abstract

The ideas originally put forth by Kolmogorov in 1941 dominate modern turbulence. It was G.K. Batchelor who introduced them to the western world after WW II and who laid out the multi-length scale view of turbulence that today underlies almost all turbulence theories and experimental interpretations, including turbulence modelling. It was the book by Tennekes and Lumley in 1972 which popularized them. So well-accepted are these ideas now that many newer books don’t even bother try to justify what we collectively refer to as K41, some simply saying they have been established by experiment.

Most think the first experimental ‘proof’ was the Grant et al. in the Vancouver Sound tidal channel. But in fact it was by M.M. Gibson in a jet in the Maryland Hall laboratory of S. Corrsin (Nature 1961) at the Johns Hopkins University. (Gibson to this day does not understand why Corrsin did not co-author the paper, but at that time Corrsin often seemed to leave his name off his students’ work usually to their detriment.)

Interestingly the experiments cited in support of K41 are almost entirely experiments in statistically stationary turbulence, so the  K41 zeroth hypothesis of local equilibrium of the small scales is satisfied by default. Statistically non-stationary experiments are more often labelled as ‘anomalous’, and alternative theories explaining them ignored. But the inconsistencies mount. Oran in her Otto Laporte lecture at the APS/DFD meeting several years ago detailed a number of high Reynolds number simulations that were ‘non-Kolmogorov’ and the experiments of the Vassilicos group at Imperial College using fractal generators have been similarly problematical.

This seminar will examine a number of Kolmogorov’s hypotheses and inferences by others from them. Receiving particular attention will by the idea of a universal equilibrium range (Batchelor chap 5), the zeroth law of turbulence (ε α u3/L), whether ηK  = (ν3)1/4  is truly the smallest length scale, and finally whether there is ever ‘local equilibrium’ in a statistically non-stationary flow. Some alternative ideas will be proposed.

Bio

Born in Camp Shelby, Mississippi in 1945, George graduated from Cambridge, Maryland High School as valedictorian in 1963. He attended the Johns Hopkins University in Baltimore, Maryland on a Maryland State Senatorial scholarship and received his BES degree from in 1967 in Engineering Physics. He continued at Johns Hopkins for doctoral work and received his Ph.D. Degree in Mechanics under the supervision of John L. Lumley in 1971. In 1968, he joined the faculty of the Pennsylvania State University, University Park, where he held positions in both Aerospace Engineering and the Applied Research Laboratory. In 1974, he left Pennsylvania State University and joined the Department of Mechanical and Aerospace Engineering at the State University of New York at Buffalo. He was promoted to Professor in 1980. George joined the Department of Applied Mechanics at the Chalmers University of Technology, Gothenburg, Sweden in September 2000 as Professor of Turbulence. Since retiring as Professor Emeritus from Chalmers in 2009, he has held positions with CNRS and Ecole Central de Lille in France, Imperial College of London, and Princeton University.

WKG has authored several hundred papers, mostly on turbulence and its applications. The number of citations of his work is measured in thousands, and his h-factor is above 30 (Numbers compiled from Google Scholar. Note that the average number of citations for papers in the leading fluids journals is less than 2.). He is known for his work on both theoretical and experimental turbulence. His contributions range from measurements in gas turbines and automotive components to fundamental studies of turbulent shear and wall bounded flows. Among his most significant contributions was the translation and editing in 1980-81 of WIND ATLAS FOR DENMARK, which provided a methodology for siting wind generators and has contributed much to the increasing popularity of this technology in Europe and around the world. He has supervised 29 PhD students and a large number of MSc students, all of whom hold responsible positions as professors, researchers, or engineers in leading establishments throughout the world. His academic descendents now extend through five generations and number more than 100.

Professor George has lectured extensively throughout the world and has presented numerous invited talks, including the 2006 AIAA Fluid Dynamics meeting, the 2003 American Physical Society/Division of Fluid Dynamics meeting, and the 2001 Australasian Fluid Mechanics meeting, among others.. Among his fellowships, honors and awards, the most recent are the 2008 Freeman Scholar Award from the ASME, the 2008 DCAMM scholar award from the Danish Center for Applied Mathematics and Mechanics, and the Ph.D. Supervisor of the Year award from Chalmers University in 2006. He was also a distinguished research fellow of the British Royal Engineering Academy and CNRS. Together with a former student and grandstudent, he received the Robert T. Knapp Award from the ASME Fluids Engineering Division 2002 for the best paper in 2001. He has been a Fellow of the American Physical Society since 1988. He is also a Fellow of the ASME and an Associate Fellow of the AIAA. From 2010 to 2012 he was named by the EU as Marie Curie Professor at Imperial College of London, and since has retained an appointment there as Senior Research Investigator. For the academic year 2013-2014 he was William R. Kenan Jr Professor of Distinguished Teaching at Princeton University.



Upcoming Seminar

Speaker: Prof. Lakshmi Dasi (Ohio State University)
Title: "Towards Precision Medicine Approach for Trans-catheter Aortic Valve Replacement"

Date: Friday, October 26, 2018
Time: 3:00 p.m.
Location: Gilman Hall 132

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