Richard J.A.M. Stevens

Physics of Fluids

University of Twente

Publication 115 · Thermal convection

How imposed shear reorganizes convective heat transport

G.S. Yerragolam, C.J. Howland, R.J.A.M. Stevens, R. Verzicco, O. Shishkina, and D. Lohse, Journal of Fluid Mechanics 1000, A74 (2024).

The article and figure are open access under CC BY 4.0.

Main finding

Across the tested Couette- and Poiseuille-forced DNS, ReS/ReR organized a common non-monotonic response: moderate shear reoriented and swept thermal plumes, lowering Nu by 18%–26% at the sampled minima, whereas stronger shear produced recovery or enhancement and a friction response consistent with Prandtl's logarithmic law.

Time-averaged temperature field and velocity streamlines in sheared Rayleigh-Bénard convection, showing spanwise plume reorientation and streamwise sweeping
How to read the figure. The three-dimensional view shows the time-averaged reduced-temperature field in Couette–Rayleigh–Bénard convection at Ra = 107, Pr = 1, Rew = 1414, Γx = 48, and Γy = 24, averaged over 100 free-fall times. Green curves are streamlines of the mean velocity after subtracting the imposed wall speed. Their predominantly spanwise circulation and the diagonally swept temperature structures show how imposed streamwise shear reorients the plumes; the lower inset resolves the corresponding temperature and velocity vectors in an x–z section. This figure supports the plume-reorientation and heat-transport-reduction mechanism, but it does not itself show the 18%–26% minima or the stronger-shear recovery, which come from the transport data and scaling analysis elsewhere in the paper. Open the full-resolution figure. Figure 5, cropped. G.S. Yerragolam et al. (2024), CC BY 4.0.

Why this matters

The ratio of imposed-shear strength to the Reynolds number of the unsheared convection wind provides a common organizing variable for Couette- and Poiseuille-forced convection. At moderate shear, the imposed streamwise motion competes with the large-scale circulation, reorients and sweeps the thermal plumes, and can trap heat in the bulk faster than it diffuses through the wall layers, reducing Nu. At stronger shear, the response crosses toward forced-convection behaviour and heat transport recovers or increases. This explains why imposed shear does not produce a monotonic heat-transfer response.

Research context

The study combines AFiD direct numerical simulations with a Grossmann–Lohse-style theory for horizontally periodic, smooth-wall Couette–Rayleigh–Bénard and Poiseuille–Rayleigh–Bénard systems. The reported scaling relations were tested mainly over 106 ≤ Ra ≤ 108, 0.5 ≤ Pr ≤ 5, and 0 ≤ ReS ≤ 104. They require unsheared reference values and have not been validated outside the sampled parameter range. The paper provides no experimental or independent-solver validation, confidence intervals, or exact averaging durations for every simulation; its proposed high-Ra pure-convection friction relation remains exploratory.

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