15 avril 2021

Webinar Genta Kawahara

Dr. Genta Kawahara received his Ph.D. in Engineering from Osaka University in 1994. He became an Associate Professor at the Faculty of Engineering, Ehime University in 1996. After staying as a Visiting Scholar at the Center for Turbulence Research, NASA Ames Research Center/Stanford University, he became an Associate Professor at the Graduate School of Engineering, Kyoto University in 2001. He was appointed to a full Professor at the Graduate School of Engineering Science, Osaka University in 2005 and became the Dean of the Graduate School of Engineering Science in 2013. He was appointed as an Executive Vice President at Osaka University in 2017. He is now an Associate Editor of the Journal of Fluid Mechanics. Dr. Kawahara has worked on the theoretical characterization of turbulent flows in terms of simple invariant solutions to the Navier-Stokes equation. He has also described the process of subcritical transition to turbulence using dynamical systems theory. Dr. Kawahara is now tackling the ultimate heat transfer in wall-bounded thermal convection and shear flow, where not only the energy dissipation rate but also the wall heat flux are independent of viscosity or thermal conductivity.
Ultimate heat transfer in turbulent convection and turbulent shear flow

Abstract: Direct numerical simulations have been performed for turbulent heat transfer in thermal convection and shear flow between parallel permeable walls, on which the transpiration velocity is assumed to be proportional to the local pressure fluctuations (Jimenez et al. 2001 J. Fluid Mech. 442, 89-117). Turbulent heat transfer has been found to be substantially enhanced by the appearance of large-scale turbulence structures (large-scale thermal plumes in convection or large-scale spanwise rolls in shear flow) arising from the wall permeability. At high Rayleigh numbers or high Reynolds numbers we have achieved the ultimate heat transfer represented by a wall heat flux being independent of thermal conductivity, although the heat transfer on the wall is dominated by thermal conduction. The key to the achievement of the ultimate heat transfer is interpreted in terms of significant heat transfer enhancement by large-scale intense turbulence with the length scale of the order of the wall distance and with the velocity scale comparable to the buoyancy-induced terminal velocity in convection or the bulk-mean velocity in shear flow without flow separation from the permeable walls.

Reference: K. Kawano, S. Motoki, M. Shimizu & G. Kawahara 2021 J. Fluid Mech. 914, A13

15 avril 2021, 16h3017h30
Webinar (please contact F. Romano for the link)