On the absence of the ultimate regime in turbulent thermal convection

• 成果类型: Article
• 署名作者: Tiwari, Harshit; Sharma, Lekha; Verma, Mahendra K.
• 署名单位: Indian Institute of Technology System (IIT System); Indian Institute of Technology (IIT) - Kanpur; Indian Institute of Technology System (IIT System); Indian Institute of Technology (IIT) - Kanpur
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2513474122
• 发表日期: 2025-10-31
• 页码: e2513474122
• 关键词: turbulent convection; turbulent heat transport; ultimate regime of convection; Rayleigh-Benard convection; compressible convection; heat-transport; numerical-simulation

摘要

Quantifying heat transport in turbulent convection remains a challenge. The two competing models of heat transport predict that the nondimensional heat flux, known as the Nusselt number (Nu), is proportional to Ra1/3 (classical scaling) and Ra1/2 (ultimate-regime scaling), where Ra is the Rayleigh number. Some experiments and simulations report that the Nusselt number transitions from near classical scaling, Ra0.30, to a larger power law when the boundary layer turns turbulent near Ra approximate to 1014. However, others find Ra0.30 scaling to continue for larger Ra. In this work, we perform a comparative study of Rayleigh-B & eacute;nard, compressible, and periodic convection in two and three dimensions using direct numerical simulations. We show that up to Ra = 1016 in two dimensions and up to Ra = 1013 in three dimensions, the positive and negative energy fluxes in Rayleigh-B & eacute;nard and compressible convection are nearly equal. However, in the distribution function, the positive fluxes have longer tails than the negative ones, and the differences between the positive and negative fluxes scale as Ra-0.20, which leads to Nu similar to Ra0.30.The above robust and universal properties, even in the presence of a logarithmic layer in compressible convection, indicate a likely absence of the ultimate regime in turbulent thermal convection. In contrast, periodic convection, which is related to the ultimate regime, exhibits a predominantly positive heat flux.