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|Title:||Simulation of air-water interfacial mass transfer driven by high-intensity isotropic turbulence|
|Publisher:||Cambridge University Press|
|Citation:||Journal of Fluid Mechanics|
|Abstract:||Previous direct numerical simulations (DNS) of mass transfer across the air-water interface have been limited to low-intensity turbulent flow with turbulent Reynolds numbers of RT 6 500. This paper presents the first DNS of low-diffusivity interfacial mass transfer across a clean surface driven by high-intensity (1440 6 RT 6 1856) isotropic turbulent flow diffusing from below. The detailed results, presented here for Schmidt numbers Sc = 20 and 500, support the validity of theoretical scaling laws and existing experimental data obtained at high RT . In the DNS, to properly resolve the turbulent flow and the scalar transport at Sc = 20 up to 524 × 106 grid points were needed, while 65.5 × 109 grid points were required to resolve the scalar transport at Sc = 500, which is typical for oxygen in water. Compared to the low RT simulations, where turbulent mass flux is dominated by large eddies, in the present high RT simulation the contribution of small eddies to the turbulent mass flux was confirmed to increase significantly. Consequently, the normalised mass transfer velocity was found to agree with the R −1/4 T scaling, as opposed to the R −1/2 T scaling that is typical for low RT simulations. At constant RT , the present results show that the mass transfer velocity KL scales with Sc−1/2 , which is identical to the scaling found in the large-eddy regime for RT 6 500. As previously found for a no-slip interface, also for a shear-free interface the critical RT separating the large from the small eddy regime, was confirmed to be about RT = 500.|
|Appears in Collections:||Dept of Mechanical Aerospace and Civil Engineering Research Papers|
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