Direct Numerical Simulation Reveals Heat-Transfer Scaling in Ultimate Regime of Rayleigh-Darcy Convection
Researchers performed computational simulations of convection in porous media across a wide range of conditions (Ra = 10³ to 10⁶) and identified a transition to an "ultimate regime" at Ra ≈ 4×10⁵ where heat transfer scales linearly with the driving force. The study found that thermal boundary layers become thinner and finer plume structures emerge at higher conditions, with heat dissipation shifting from walls to the bulk fluid. This work advances understanding of convective heat transfer in porous materials, relevant to geothermal systems, subsurface flows, and thermal engineering applications.
Direct numerical simulations (DNS) of Rayleigh-Darcy convection in three-dimensional porous domains reveal previously unexplored physics at high Rayleigh numbers. The Nusselt number (Nu), which quantifies heat-transfer efficiency, exhibits approximately linear dependence on the Rayleigh number (Ra) across the investigated range, with a distinct change in slope at Ra ≈ 4×10⁵ marking the onset of the ultimate regime. The study shows that thermal boundary-layer thickness scales as Ra⁻¹, and detailed flow analysis reveals the formation of small-scale near-wall structures called protoplumes that merge into larger columnar megaplumes. As Ra increases, protoplumes become finer and more numerous, enhancing heat transport efficiency. The thermal dissipation pattern shifts progressively from boundary layers toward the bulk fluid at higher Ra, indicating that finer plume structures efficiently transport heat from walls throughout the domain.
What's missing
The study does not discuss potential experimental validation of these DNS predictions, practical applications or implications for real-world porous media systems (such as geothermal reservoirs or building materials), or computational cost and scalability considerations for even higher Ra numbers.
What different sources said
- arXiv physicsCenter
Ultimate regime in Rayleigh-Darcy Convection
Related
Topology-Aware Thermodynamics Improves DNA Probe Specificity Design
Researchers developed a new framework for designing DNA probes that accounts for the spatial organization of matched sequences, not just overall thermodynamic stability. Traditional methods rely on scalar measures like melting temperature and free energy, which miss how mismatches are distributed along the probe. The approach could improve diagnostic accuracy in applications like HPV detection and gene expression profiling.
Study Identifies Optimal Thermal Dose for Combining Focused Ultrasound with Immunotherapy in Tumors
Researchers used multimodal PET imaging to identify an optimal thermal dose range for focused ultrasound ablation that destroys tumor tissue while preserving conditions for immunotherapy delivery. The study found that excessive heating collapses blood vessels needed for antibody access, while insufficient heating fails to adequately reduce tumor burden. The findings could guide clinical design of combination treatments pairing thermal ablation with immunotherapies.
Plant MSH1 Protein Functions as Mismatch-Directed Nuclease for Organelle Genome Maintenance
Researchers have identified the precise mechanism by which the AtMSH1 protein in Arabidopsis plants recognizes and cleaves DNA mismatches and lesions, preventing mutations in organellar genomes. The protein combines a DNA mismatch recognition module with a nuclease domain that makes staggered cuts at specific positions relative to DNA damage. This discovery explains how plants maintain unusually low mutation rates in their mitochondrial and chloroplast DNA compared to other eukaryotes.