Roughness-facilitated local 1/2 scaling does not imply the onset of the ultimate regime of thermal convection

Zhu, X.; Stevens, R.J.A.M.; Verzicco, R.; Lohse, D.

doi:10.1103/PhysRevLett.119.154501

Publication 46 · Thermal convection

Roughness-facilitated local 1/2 scaling does not imply the onset of the ultimate regime of thermal convection

X. Zhu, R.J.A.M. Stevens, R. Verzicco, D. Lohse, Phys. Rev. Lett. 119, 154501 (2017).

Main finding

The return from one half to one third provides strong bounded evidence that a finite local one-half exponent is not sufficient to identify the ultimate regime. The bulk/boundary-layer sequence is a physically supported interpretation, not a causally isolated universal mechanism.

Heat transport against Rayleigh number for smooth and three rough cases, with two regimes marked — **How to read the figure.** Nusselt number against Rayleigh number for a smooth cell and three roughness configurations, with regimes I and II labelled. The inset compensates by the square root of Rayleigh number: the rough cases hold a near-half-power slope through regime I and then return towards smooth-wall behaviour in regime II. Open the full-resolution figure. Figure 2. X. Zhu et al. (2017). No separate licence is stated here; consult the original publication and credited source before reuse.

Why this matters

The same apparent one-half law can arise temporarily from roughness and then disappear.

Research context

The simulated sequence moves from plume-mediated, bulk-dominated transport to thin thermal layers coating the rough surface at higher Rayleigh number. The accompanying Taylor–Couette comparison is contextual and does not transfer that Rayleigh–Bénard mechanism automatically.

Read the article View in the complete publication list Related thermal convection research