{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"46a18671ca10dd705c5ad78c890bbfc385d84b930c6b8604ac05e9e5f1958c8d","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":["ai:gpt-5.5"],"kind":"seed"},"parents":["85dd425d0406ee8137d83fbe9d8f46d182913088e4accf3e89a2eb102f2072b0","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"dd34b06435a9068e0b11d599867deb4650c6dc51ae66727f4cf98dc6fefb2785","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":["ai:gpt-5.5"],"external_id":"fluid.rb-convection.transition-onset","kind":"well-posed","literature_status":"contested","n":"2","parents":[],"plain":"If the steep heat-transport regime exists, it starts at very different heating strengths in different experiments. What fixes the starting point is unknown.","posed_since":"","precise":"Assuming a transition exists, determine how the onset Rayleigh number $Ra*$ depends on Pr, aspect ratio $\\Gamma$, plate and sidewall conditions and residual perturbations, and whether onset corresponds to a universal critical shear Reynolds number $Re_{s}$ of the plate boundary layers (Grossmann-Lohse estimate $Re_{s} \\sim 420$, approximately). Answer: a predictive criterion for $Ra*$, or a demonstration that the onset is a subcritical, perturbation-dependent transition with no single $Ra*$.","problem_ref":"85dd425d0406ee8137d83fbe9d8f46d182913088e4accf3e89a2eb102f2072b0","references":"","settled_by":"Systematic experiments in one apparatus varying $\\Gamma$, Pr and controlled boundary-layer perturbations, mapping $Ra*$ against $\\mathrm{Re}_{s}$.","status_note":"Reported onsets range from $\\mathrm{Ra}\\sim 10^{11}$ to above $10^{14}$; Shishkina and Lohse (2024, arXiv:2407.16573) argue onset occurs in all large-Ra data sets at experiment-dependent Ra, as expected for a non-normal nonlinear instability.","title":"What sets the Rayleigh number of the transition to ultimate 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