Description
We have run a series of model experiments to study the properties of turbulent convection in a rectangular cell at Rayleigh numbers or order 10^8 to 10^9 and Prandtl number Pr=6.1 for water, with uniformly heated bottom solid boundary and free upper surface (quasi-stationary heat flux). Two cases of the horizontally extended cell aspect ratio were considered: 2:1:1, characterized by the presence of a pronounced stable cell large-scale circulation, and 4:4:1, characterized by an ensemble of quasi-stationary convective cells. Laboratory measurements using stereoPIV method enable us to run long time series to accumulate sufficiently reliable statistical data. Furthermore, numerical simulations provide three-dimensional vector velocity fields with high resolution. We compare experimental and numerical results in the overlapping range of parameters. The spatial and temporal correlation scales in the bulk of the turbulent flow are obtained by correlation and wavelet analysis.
Qualitative Results of analysis of experiments are as follows:
1. We have established that persistent large scale structures (circulation cells) exist for several hundreds of turnover times without significant changes of their shape.
2. Numerical experiments gave a solution which agrees with laboratory modeling for the mean flow and rms turbulent pulsations in the bulk of the medium.
3. Due to surface phenomena of water, the boundary conditions occur to be close to a stiff boundary layer (no-slip and no-penetration conditions). It was confronted with a comparative experiment with silicon oil on convection with open boundary conditions (free-slip flow).
4. We have achieved qualitative scale separation between large scale structures and turbulent eddies, both in numerical and laboratory experiments. The correlation lengths in vertical direction are several times smaller than the vertical size of the entire setup. Thus, we have shown that the properties which have earlier been found for air convection by Elperin et al. (2006) and Bukai et al. (2009) can qualitatively be extended for convection of liquids. The data enable one to compute some components of statistical correlators that enter the meanfield MHD dynamo equations. These results are of interest to understanding geophysical and astrophysical flows. The work is supported by RSF grant 21-72-20067.
1. Elperin, Tov ; Golubev, Ilia ; Kleeorin, Nathan ; Rogachevskii, Igor // Physics of Fluids, Volume 18, Issue 12, pp. 126601-126601-11 (2006)
2. Bukai, M. ; Eidelman, A. ; Elperin, T. ; Kleeorin, N. ; Rogachevskii, I. ; Sapir-Katiraie, I.// Physical Review E, vol. 79, Issue 6, id. 066302 (2009)
