Turbulent Heat Transfer in Wall-Bounded Flows – Genta Kawahara (Osaka University)

January 6, 2022 @ 1:00 pm – 2:00 pm
Seminar Room 1
Newton Institute

If there is a difference in temperature between the bulk fluid and the wall surface in wall-bounded turbulent flows, such as thermal convection and shear flow, heat will be transferred between the fluid and the wall. This is (convection) heat transfer, which is dominated by thermal conduction but highly depends on flow characteristics. Turbulent heat transfer is a significant problem not only in fluid mechanics but also in a wide variety of engineering applications.In the first part of this talk, turbulent heat transfer in Rayleigh-Bénard convection will be reviewed, with emphasis on widely observed scaling properties, i.e. the classical scaling, as well as the so-called ultimate scaling (corresponding to the Taylor dissipation law, i.e. inertial energy dissipation) suggested for extremely high Rayleigh numbers, implying that a wall heat flux is independent of thermal conductivity. Similarity and dissimilarity between heat and momentum transfer will also be reviewed for wall-bounded turbulent shear flows, in which the Taylor’s inertial dissipation does not necessarily correspond to the ultimate heat transfer.In the second part, the feasibility of the ultimate heat transfer will be explored in turbulent Rayleigh-Bénard convection and turbulent channel flow. Wall permeability, which can be implemented on a porous wall, is introduced in thermal convection and turbulent shear flow. It is found that in both thermal convection and shear flow between the permeable walls, the ultimate heat transfer can be achieved at high Rayleigh numbers and high Reynolds numbers, respectively. It will be demonstrated why the wall permeability can lead to the ultimate scaling in wall-bounded convective turbulence and sheared turbulence.

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