Study of unsteady natural convection induced by absorption of radiation based on a three-waveband attenuation model

21st Fluid Mechanics Conference

物理学;力学

Hattori, T.^1 ; Patterson, J.C.^1 ; Lei, C.^1

School of Civil Engineering, University of Sydney, Sydney, NSW, Australia^1

关键词: Attenuation coefficient;    Bottom boundary layer;    Direct absorption;    Lake sand reservoirs;    Residual radiation;    Two-dimensional numerical simulation;    Unsteady natural convection;    Wavelength dependency;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/530/1/012036/pdf
DOI  :  10.1088/1742-6596/530/1/012036

学科分类：力学，机械学

来源: IOP

【 摘 要 】

The present study considers unsteady natural convection induced by the absorption of radiation for possible applications in the water quality management for the shallow regions of lakes and reservoirs. The direct absorption of the incoming radiation by the water body forms a stable thermal stratification, whilst residual radiation reaching the bottom bathymetry is re-emitted as a boundary flux, forming an unstable thermal stratification, which is a potential source for a Rayleigh-Benard type instability. The bottom boundary layer instability drives intermittent vertical convection in the form of rising plumes. The plume rise is, however, limited by the stable thermal stratification due to the direct absorption, which is controlled by the attenuation coefficient of water. The attenuation coefficient is therefore an important parameter in determining the plume rise and the associated vertical mixing. The wavelength dependency of the attenuation coefficient of water is accounted for by using a three-waveband model. A theoretical prediction is made for the plume rise distance, which represents the region of vigorous mixing. Two-dimensional numerical simulation provides verification for the accuracy of the theoretical prediction.