Richard J.A.M. Stevens

Professor at the University of Twente

Wind energy · Turbulence · Environmental flows

Publication 49 · Thermal convection

Transition to the ultimate regime in two-dimensional Rayleigh-Bénard convection

X. Zhu, V. Mathai, R.J.A.M. Stevens, R. Verzicco, and D. Lohse, Phys. Rev. Lett. 120, 144502 (2018).

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Main finding

The Letter supplies a coherent multi-diagnostic candidate transition near Ra=10^13, stronger than an exponent-only claim. It does not by itself uniquely establish turbulent boundary layers or an ultimate regime because the profile fits, breakpoint, numerical fidelity, uncertainty, state sensitivity, conditional decomposition, and later formal dispute remain unresolved.

Local heat flux in ejecting and impacting wall regions against Rayleigh number
How to read the figure. Compensated Nusselt number measured separately over the ejecting and the impacting regions of the plate. Above a Rayleigh number of about 10^13 the two follow different power laws, Ra^0.38 and Ra^0.28, so the two wall regions change differently as convection intensifies. Open the full-resolution figure. Figure 4. X. Zhu et al. (2018). No separate licence is stated here; consult the original publication and credited source before reuse.

Why this matters

Different wall regions can change differently as convection intensifies, producing a gradual global transition.

Research context

Earlier roughness evidence: Roughness-facilitated local 1/2 scaling does not imply the onset… (read the finding) shows that a local near-half-power interval under mono-scale roughness does not imply the ultimate regime; Nu ∼ Ra^1/2 scaling enabled by multiscale wall roughness… (read the finding) extends that finite interval with multiscale roughness. These rough cases do not validate the smooth-wall transition claimed here.

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