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Results of DNS are reported for turbulent Rayleigh-Bénard mercury convection (Pr = 0.025) in a cylindrical container with the aspect ratio of unity at the Rayleigh number of Ra = 106. The main goal of the study is to estimate the influence of small deviations from the axisymmetric formulation on the behavior of large-scale circulation (LSC) developing in the container. The deviations examined are a small tilt of the cylinder or prescribed sinusoidal disturbances of the bottom wall temperature. The effects of the computational grid structure in the central region of the flow are investigated as well. It has been shown that the azimuthal low-frequency reorientations of the LSC, which are typical for the axisymmetric problem setting, can be fully suppressed by imposing relatively small non-axisymmetric disturbances of various kinds. Time-averaged 3D velocity and temperature fields, as well as spatial non-uniformities of local heat transfer are analyzed for a “locked” LSC case.

The paper presents the results of the numerical study of the flow in a symmetric model of the venous valve with different leaflet elasticity. The focus is on the analysis of the velocity field and the stagnant region. The stagnant region behind the valve is of great practical interest for phlebologists in terms of the potential for the formation of blood clots. The constructed simplified model of the venous valve has given a good qualitative agreement with the clinical ultrasound data on the position of the valve leaflet and the stagnant zone behind the valve.

KEY WORDS: integrated power supply of separate facilities, renewable energy sources, alternative energy ABSTRACT:The relevancy of the study is due to low efficiency of using solar and geothermal energy in the existing process schemes. In this regard, this article is aimed at revealing the possibilities of using solar and geothermal energy for the integrated energy supply of separate facilities from renewable energy sources. The mathematical simulation method based on the theory of graphs of energy system operation, which makes it possible to analyze the efficiency of the integrated use of solar and geothermal energies for the heat-cold supply of separate facilities, is the main approach to studying this problem. Energy consumption throughout the year and the emergency energy source capacity in "peak" modes were determined based on the developed mathematical model of managing the system of integrated power supply of separate facilities from renewable energy sources plotted with the use of the theory of graphs. The article materials are of practical value for the designers of the systems of integrated heat-cold supply of separate facilities.

<p>The features of turbulent heat and mass transfer in a stratified fluid exposed by periodical inhomogeneous volumetric heating are of great practical and fundamental interest. Such phenomena take place in geophysical flows, for example, in ice-covered boreal lakes in spring, where the mechanisms and efficiency of mixing of water masses has a great effect on chemical and biological processes in lakes [1, 2]. Detailed numerical modeling of such flows coupled with experimental observations makes it possible to reveal some important aspects of the structure and parameters of under-ice turbulence, the nature and properties of its anisotropy, difference in the spectra of vertical and horizontal pulsations, and features of energy transfer. This work presents preliminary results of both experimental and numerical investigations of the radiatively-driven free turbulent under-ice convection. The aim of this work is to study the initial stages of the formation and development of a convective mixed layer as well as comparison with obtained experimental data. Numerical simulation is based on the results presented in [3], where the LES study of the development of the convective mixed layer under constant radiation heating was considered. In this study, the radiation heat flux at the ice-water interface is a periodic function evaluated by approximation of the experimental data presented at [4]. These data were obtained during investigations of the under-ice convection in the lake Vendyurskoe at springtime of 2020. The computations were carried out using the in-house finite-volume «unstructured» code SINF/Flag-S developed at Peter the Great St. Petersburg Polytechnic University. We show that the results on the rates of temperature increase and deepening of the convective mixed layer are in good agreement with our experimental data.</p><p>The study is supported by the Russian Science Foundation under grants no. 21-17-00262 “Mixing in boreal lakes: mechanisms and its efficiency”.</p><p><strong>REFERENCES</strong></p><p><em>1. Bouffard, D., Wüest, A.</em>, 2019. Convection in Lakes. <em>Ann. Rev. of Fluid Mechanics</em> 51: 189-215.</p><p><em>2. Bouffard, D., Zdorovennova, G., Bogdanov, S. et al,</em> 2019. Under-ice convection dynamics in a boreal lake. <em>Inland Waters</em> 9: 142-161.</p><p><em>3. Mironov, D., Terzhevik, A., Kirillin, G., et al,</em> 2002. Radiatively driven convection in ice-covered lakes: Observations, scaling, and a mixed layer model. <em>J. Geophys. Res.</em> 107: 1-16.</p><p><em>4. Bogdanov, S.R., Zdorovennov, R.E., Palshin N.I. et al, </em>2021. Deriving of turbulent stresses in a convectively mixed layer in a shallow lake under ice by coupling two ADCPS. <em>Fundamental and Applied Hydrophysics</em> 14: 17-28.</p>