How small-scale flow structures affect the heat transport in sheared thermal convection

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Abstract

We investigate the counter-intuitive initial decrease and subsequent increase in the Nusselt number NuNu with increasing wall Reynolds number RewRew in the sheared Rayleigh–Bénard (RB) system by studying the energy spectra of convective flux and turbulent kinetic energy for Rayleigh number Ra=107Ra=107, Prandtl number Pr=1.0Pr=1.0 and inverse Richardson numbers 0≤1/Ri≤100≤1/Ri≤10. These energy spectra show two distinct high-energy regions corresponding to the large-scale superstructures in the bulk and small-scale structures in the boundary layer (BL) regions. A greater separation between these scales at the thermal BL height correlates to a higher NuNu and indicates that the BLs are more turbulent. The minimum NuNu, which occurs at 1/Ri=1.01/Ri=1.0, is accompanied by the smallest separation between the large- and small-scale structures at the thermal BL height. At 1/Ri=1.01/Ri=1.0, we also observe the lowest value of turbulent kinetic energy normalized with the square of friction velocity within the thermal BL. Additionally, we find that the domain size has a limited effect on the heat and momentum transfer in the sheared RB system as long as the domain can accommodate the small-scale convective structures at the thermal BL height, signifying that capturing the large-scale superstructures is not essential to obtain converged values of NuNu and shear Reynolds number ReτReτ. When the domain is smaller than these small-scale convective structures, the overall heat and momentum transfer reduces drastically.


Original languageEnglish
Article numberA1
JournalJournal of fluid mechanics
Volume944
Early online date22 Jun 2022
DOIs
Publication statusPublished - 10 Aug 2022

Keywords

  • Fluid mechanics
  • Fluid dynamics
  • turbulence
  • direct numerical simulations
  • High performance computing
  • heat transfer
  • Rayleigh Benard
  • Convection
  • shear flow
  • UT-Hybrid-D

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