The radiatively-driven turbulent convection in ice-covered lake: numerical and observational study

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.

The study is supported by the Russian Science Foundation under grants no. 21-17-00262 “Mixing in boreal lakes: mechanisms and its efficiency”.

REFERENCES

1. Bouffard, D., Wüest, A., 2019. Convection in Lakes. Ann. Rev. of Fluid Mechanics 51: 189-215.

2. Bouffard, D., Zdorovennova, G., Bogdanov, S. et al, 2019. Under-ice convection dynamics in a boreal lake. Inland Waters 9: 142-161.

3. Mironov, D., Terzhevik, A., Kirillin, G., et al, 2002. Radiatively driven convection in ice-covered lakes: Observations, scaling, and a mixed layer model. J. Geophys. Res. 107: 1-16.

4. Bogdanov, S.R., Zdorovennov, R.E., Palshin N.I. et al, 2021. Deriving of turbulent stresses in a convectively mixed layer in a shallow lake under ice by coupling two ADCPS. Fundamental and Applied Hydrophysics 14: 17-28.