Talks at Nordita Programs [before October 2010]
High Reynolds Number Wall-Bounded Turbulence: Approach to Asymptotic State, Universality and ICET
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Europe/Stockholm
FB52
FB52
Description
Just over one-hundred years ago Prandtl introduced the new concept of "boundary layers" to
explain, analyze and model fluid flow behavior near surfaces. Since then, the method of matched asymptotics has contributed a great deal to our understanding of turbulent boundary layers, starting with the classical two-layer approach of Millikan, which leads to the logarithmic velocity profile in the overlap region between "inner or small scales" and "outer or large scales," and the von Kármán constant. Nearly all currently used commercial codes for computation of flow in applications including aeronautics, energy generating machines and weather prediction rely on such a von Kármán constant. We examine the overlap parameters of the logarithmic law for available experimental and computational date from turbulent boundary layer, pipe and channel flows, over wide ranges of Reynolds numbers, using composite profiles fitted to the mean velocity. This reveals that boundary layers with streamwise pressure gradients, and pipe and channel flows display von Kármán coefficients that are not universal. Therefore, we conclude that the von Kármán constant exhibits dependence on not only the pressure gradient but also the wall-bounded flow geometry, thereby raising fundamental questions regarding turbulence flow theory and modeling for all wall-bounded flows. The zero pressure gradient (ZPG) boundary layers are one of the canonical, wall-bounded, turbulent flows that have been the focus of experimental and analytical investigations for several decades. Over the past few years, four groups have focused on systematic comparison between several measurement techniques and
three facilities. Two closed return wind tunnels with ZPG boundary layers developed on a
plate suspended near the mid-height of the test section (at KTH and IIT), and an open return
facility with a large and long test section and a boundary layer developing along its floor (at the University of Melbourne), are used for these coordinated efforts. The development-length of the boundary layers and the free-stream velocity in the three facilities range from 5.5 to 21 m, and from 10 to 60 m/s, respectively. Various arrangements for adjustable test section ceilings are employed to generate ZPG boundary layers over the range of momentum thickness Reynolds numbers from 11,000 to 70,000. Oil film interferometry (OFI) is employed to directly measure the wall shear stress, and various sizes of Pitot probes and types of hot-wire sensors are used to measure wall-normal velocity profiles at different locations and free-stream velocities.
Professor Nagib is the John T Rettaliata Distinguished Professor of Mechanical and Aerospace Engineering at the Illinois Institute of Technology, Chicago, Illinois, and the Founding Director of the Institute’s Fluid Dynamics Research Center. He is also an Affiliated Professor in Mechanics Department of KTH. His field of specialty is in fluid mechanics, turbulent flow and flow management and control. Professor Nagib is the recipient of a number of prestigious honors including being a Fellow of the American Physical Society, the American Association of Advancement of Science, the American Institute of Aeronautics and Astronautics, and the American Society of Mechanical Engineers.
Professor Nagib is the John T Rettaliata Distinguished Professor of Mechanical and Aerospace Engineering at the Illinois Institute of Technology, Chicago, Illinois, and the Founding Director of the Institute’s Fluid Dynamics Research Center. He is also an Affiliated Professor in Mechanics Department of KTH. His field of specialty is in fluid mechanics, turbulent flow and flow management and control. Professor Nagib is the recipient of a number of prestigious honors including being a Fellow of the American Physical Society, the American Association of Advancement of Science, the American Institute of Aeronautics and Astronautics, and the American Society of Mechanical Engineers.