{"about":{"site":"https://codewithpapers.app","non_affiliation":"Code with Papers and Syntology are not affiliated with, endorsed by, or sponsored by Papers with Code, Meta, or the pwc-archive mirror.","licence":"CC BY-SA 4.0","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","attribution":"https://codewithpapers.app/attribution","modified":"archive material modified by Syntology; see the attribution page"},"url":"/paper/buoyancy-driven-entrainment-in-dry-thermals","title":"Buoyancy-Driven Entrainment in Dry Thermals","arxiv_id":"1906.07224","date":"2019-06-17","proceeding":null,"authors":["Brett McKim","Nadir Jeevanjee","Daniel Lecoanet"],"abstract":"\\citet{turner1957} proposed that dry thermals entrain because of buoyancy (via a constraint which requires an increase in the radius $a$). This however, runs counter to the scaling arguments commonly used to derive the entrainment rate, which rely on either the self-similarity of \\citet{scorer1957} or the turbulent entrainment hypothesis of \\citet{morton1956}. The assumption of turbulence-driven entrainment was investigated by \\citet{lecoanet2018}, who found that the entrainment efficiency $e$ varies by less than $20\\%$ between laminar (Re = 630) and turbulent (Re = 6300) thermals. This motivated us to utilize Turner's argument of buoyancy-controlled entrainment in addition to the thermal's vertical momentum equation to build a model for thermal dynamics which does not invoke turbulence or self-similarity. We derive simple expressions for the thermals' kinematic properties and their fractional entrainment rate $\\epsilon$ and find close quantitative agreement with the values in direct numerical simulations. In particular, our expression for entrainment rate is consistent with the parameterization $\\epsilon \\sim B/w^2$, for Archimedean buoyancy $B$ and vertical velocity $w$. We also directly validate the role of buoyancy-driven entrainment by running simulations where gravity is turned off midway through a thermal's rise. The entrainment efficiency $e$ is observed to drop to less than 1/3 of its original value in both the laminar and turbulent cases when $g=0$, affirming the central role of buoyancy in entrainment in dry thermals.","url_abs":"http://arxiv.org/abs/1906.07224v2","url_pdf":"http://arxiv.org/pdf/1906.07224v2.pdf","source":{"archive":"pwc-archive (Hugging Face), CC BY-SA 4.0","snapshot":"2025-07-28","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","row_kind":"links_only","authors_date_abstract":"arXiv metadata, CC0 1.0 (https://info.arxiv.org/help/license), from the Kaggle arXiv metadata snapshot of 2026-09-12"},"code_links":[{"paper_slug":"buoyancy-driven-entrainment-in-dry-thermals","repo_url":"https://github.com/mckimb/buoyant_entrainment","is_official":1,"mentioned_in_paper":1,"mentioned_in_github":0,"framework":"none","reach":null}],"tasks":[],"methods":[],"datasets_introduced":[],"methods_introduced":[],"results":[],"syntology":{"syntology_url":null,"atlas_url":null,"mcp":null,"developers":"https://syntology.ai/developers"},"arxiv_metadata":null,"syntology_extracted_results":null}