Plume or bubble? Mixed-convection flow regimes and city-scale circulations

Hamidreza Omidvar, Elie Bou-Zeid, Qi Li, Juan Pedro Mellado, Petra Klein

Research output: Contribution to journalArticlepeer-review

23 Scopus citations


Large-scale circulations around a city are co-modulated by the urban heat island and by regional wind patterns. Depending on these variables, the circulations fall into different regimes ranging from advection-dominated (plume regime) to convection-driven (bubble regime). Using dimensional analysis and large-eddy simulations, this study investigates how these different circulations scale with urban and rural heat fluxes, as well as upstream wind speed. Two dimensionless parameters are shown to control the dynamics of the flow: (1) the ratio of rural to urban thermal convective velocities that contrasts their respective buoyancy fluxes and (2) the ratio of bulk inflow velocity to the convection velocity in the rural area. Finally, the vertical flow velocities transecting the rural to urban transitions are used to develop a criterion for categorizing different large-scale circulations into plume, bubble or transitional regimes. The findings have implications for city ventilation since bubble regimes are expected to trap pollutants, as well as for scaling analysis in canonical mixed-convection flows.

Original languageEnglish (US)
Article numberA5
JournalJournal of Fluid Mechanics
StatePublished - 2020
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering
  • Applied Mathematics


  • Bénard convection
  • atmospheric flows
  • buoyant boundary layers


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