Investigation of convective heat and mass transfer in reservoirs in northern latitudes using eddy-resolving model During the construction of large hydropower systems in permafrost areas, a number of problems associated with the thermal regime of bottom soils and its effect on metabolic processes in the water column arises. For example, impounding of the reservoir of Evenkiiskaya HPS on the river Nizhnyaya Tunguska, located in Eastern Siberia near the Arctic Circle, will lead to the rise of water level by 120 m and flooding of vast areas of cryogenic soils along the 2000 km range of the river channel.
Climatic regime of Evenkia is extremely severe, and ice cover on the river is held for 9 months. During flooding the temperature of bottom layers of water is close to the temperature of melting ice, that is 0°С, while overlying layers will have a temperature typical for maximum density of water ≈ 4°С (the warmer masses will move upward as lighter ones under the influence of buoyancy). Anomalous physical properties of water in the range of 0 4°С cause a decrease in density with decreasing temperature. Chilled layers of water adjacent to the bottom with a temperature will be easier than overlying layers; and this will create conditions for the formation of density instability and development of intense convective motions. Depending on the ambient conditions the near-bottom convection can cover a vast area, became large-scale, and reach the surface horizons. Convective heat transfer in this case will contribute to the cooling of water in its entire thickness and thus influence the processes of underwater and surface ice formation.
In order to study metabolic processes a mathematical formulation of the thermodynamic interaction of the reservoir with supercooled bottom and ice cover on the free surface is presented. Simulation of turbulent flows with coherent structures is based on thermohydrodynamic equations in the Boussinesq approximation where middle (horizontally uniform) and convective (large eddies) components are isolated. Subgrid-scale motion is described using one-parameter model for the turbulent kinetic energy. Applicability of models of different classes to calculate the vertical heat transfer in deep-water reservoirs over zones of permafrost is discussed.
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