Physical controls on mixing and transport within rising submarine hydrothermal plumes: A numerical simulation study |
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| Institution: | 1. Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany;2. Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA;3. Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA, USA;4. MIT-WHOI Joint Program in Oceanography, Cambridge/Woods Hole, MA, USA;5. Institute of Marine Sciences, National Research Council, Lerici, La Spezia, Italy;6. Marine Research Institute, Reykjavík, Iceland;7. Applied Physics Laboratory, University of Washington, Seattle, WA, USA;8. Institute of Oceanography, University of Hamburg, Hamburg, Germany;9. GEOMAR, Helmholtz Centre for Ocean Research, Kiel, Germany;1. NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg, The Netherlands;2. Norwegian Polar Institute, Fram Centre, Hjalmar Johansens gt. 14, 9296 Tromsø, Norway;4. Alfred Wegener Institute for Polar and Marine Research, Climate Sciences Department, Am Handelshafen 12, 27570 Bremerhaven, Germany;5. Institute of Oceanology PAS, Physical Oceanography Department, ul. Powstancow Warszawy 55, 80-712 Sopot, Poland;1. Laboratoire de Géosciences Marines, IPGP, CNRS UMR7154, Paris, France;2. Woods Hole Oceanographic Institution, Woods Hole, MA, USA;3. VICOROB, University of Girona, Spain;4. Laboratoire Domaines Océaniques, CNRS & Université de Bretagne Occidentale, Brest, France;5. University of Modena and Reggio Emilia, Modena, Italy;6. EEP, IFREMER, Brest, France;7. Université de La Rochelle, La Rochelle, France;1. Key Laboratory of Marine Sedimentology and Environmental Geology, First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China;2. Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China |
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| Abstract: | A computational fluid dynamics (CFD) model was developed to simulate the turbulent flow and species transport of deep-sea high temperature hydrothermal plumes. The model solves numerically the density weighted unsteady Reynolds-averaged Navier–Stokes equations and energy equation and the species transport equation. Turbulent entrainment and mixing is modeled by a k–ε turbulence closure model. The CFD model explicitly considers realistic vent chimney geometry, vent exit fluid temperature and velocity, and background stratification. The model uses field measurements as model inputs and has been validated by field data. These measurements and data, including vent temperature and plume physical structure, were made in the ABE hydrothermal field of the Eastern Lau Spreading Center. A parametric sensitivity study based on this CFD model was conducted to determine the relative importance of vent exit velocity, background stratification, and chimney height on the mixing of vent fluid and seawater. The CFD model was also used to derive several important scalings that are relevant to understanding plume impact on the ocean. These scalings include maximum plume rise height, neutrally buoyant plume height, maximum plume induced turbulent diffusivity, and total plume vertically transported water mass flux. These scaling relationships can be used for constructing simplified 1-dimensional models of geochemistry and microbial activity in hydrothermal plumes. Simulation results show that the classical entrainment assumptions, typically invoked to describe hydrothermal plume transport, only apply up to the vertical level of ~0.6 times the maximum plume rise height. Below that level, the entrainment coefficient remains relatively constant (~0.15). Above that level, the plume flow consists of a pronounced lateral spreading flow, two branches of inward flow immediately above and below the lateral spreading, and recirculation flanking the plume cap region. Both turbulent kinetic energy and turbulence dissipation rate reach their maximum near the vent; however, turbulent viscosity attains its maximum near the plume top, indicating strong turbulent mixing in that region. The parametric study shows that near vent physical conditions, including chimney height and fluid exit velocity, influence plume mixing from the vent orifice to a distance of ~10 times the vent orifice diameter. Thus, physical parameters place a strong kinetic constraint on the chemical reactions occurring in the initial particle-forming zone of hydrothermal plumes. |
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| Keywords: | Hydrothermal plume hydrodynamics Hydrothermal plume turbulence Entrainment Turbulent mixing Computational fluid dynamics Turbulence modeling |
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