Turbulent natural convection in an air-water system with evaporation across the free surface
(2024) 1st European Fluid Dynamics Conference — Location: Aachen, Germany (16.September.2024)
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- Abstract
- In this talk, we present results from direct numerical simulations of turbulent convection in a pool that contains liquid water in the lower part and air in the upper one. In our setup, the bottom wall is uniformly heated which leads to the onset of natural convection in both phases, accompanied by evaporation across the free surface of the water. The descent of the free surface due to evaporation is calculated via a tracking algorithm that we developed recently 1 . In this algorithm, the jumps of the flow variables across the free surface is taken into account via the the ghost-fluid method. We consider three different cases which correspond to different pool heights. In all of them, the Rayleigh number on the liquid side is fixed at 750000 which translates to weakly turbulent natural convection. Whereas on the gas side, the Rayleigh number in the three cases is 17000 , 136000 and 1000000. Accordingly, the convection in the gas in these cases lies in the laminar, transitional and soft-turbulence regimes, respectively. In our presentation we discuss the characteristics of the convective patterns both below and above the free surface and we elaborate on the statistics of the various flow quantities of interest. According to our simulations, the flow in the water is organized in a single-roll large-scale circulation (LSC). In the gas, it is organized in single or dual-roll LSCs, depending on the aspect ratio of the pool. Interestingly, the impingement points of the LSCs of the two phases at the free surface remain very close to one another, which is attributed to the continuity of the shear stresses at the free surface. Further, after the initial transient period, both the free-surface temperature and the evaporative mass flux are stabilized and remain almost constant, but they exhibit small-scale fluctuations in time due to turbulence. Also, the transport of water vapor in air has similar properties as the heat transport, and the ratio between the Sherwood and Nusselt numbers is very close to the Lewis number for air.
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Carlier, J., & Papalexandris, M. (2024). Turbulent natural convection in an air-water system with evaporation across the free surface. 1st European Fluid Dynamics Conference, Aachen, Germany. https://hdl.handle.net/2078.5/231459