The spectral link in turbulent frictional drag
by Prof. Pinaki Chakraborty (Okinawa Institute of Science and Technology, Japan)
Monday, January 29, 2018 from to (Asia/Kolkata)
I will review the spectral link in turbulent frictional drag,the missing link between two aspects of turbulent flows that have beenthe subject of extensive, but disjoint, research effeorts: the frictional drag experienced by a turbulent flow over a wall and the turbulent spectrum. The standard theory of turbulent frictionaldrag, which is based on the pioneering work of Prandtl and von Karman, computes the frictional drag using an indirect approach and makes no contact with the spectrum. By contrast, the spectral link computes the frictional drag directly and expresses it as a functional of the turbulent spectrum. To illustrate the applications of the spectral link, I will obtain an analytical version of the arch-famous Nikuradse's diagram that is in minute qualitative agreement with the distinctive features in the diagram that have remained elusive to any theoretical elucidation. Thereafter, I will discuss unprecedented experimental measurements of frictional drag in turbulent soap-film flows over smooth walls and show how the results render the standard theory incomplete. This research is pursued in close collaboration with Gustavo Gioia (OIST); other collaborators include Nigel Goldenfeld (U. Illinois), Walter Goldburg (U. Pittsburgh), and Hamid Kellay (U. Bordeaux).