The time evolution of a two-dimensional line thermal-a turbulent flow produced by an initial element with significant buoyancy released in a large water body, is numerically studied with the two-equation k - epsilon m...The time evolution of a two-dimensional line thermal-a turbulent flow produced by an initial element with significant buoyancy released in a large water body, is numerically studied with the two-equation k - epsilon model for turbulence closure. The numerical results show that the thermal is characterized by a vortex pair flow and a kidney shaped concentration structure with double peak maxima; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless time around 10. There are two regions in the flow field of a line thermal: a mixing region where the concentration of tracer fluid is high and the flow is turbulent and rotational with a pair of vortex eyes, and an ambient region where the concentration is zero and the flow is potential and well-described by a model of doublet with strength very close to those given by early experimental and analytical studies. The added virtual mass coefficient of the thermal motion is found to be approximately 1. The aspect ratio for the kidney-shaped sectional thermal is found to be around 1.45 for the self-similar phase. The predicted thermal spreading and mixing rate compares well with experimental data.展开更多
基金The project was supported by the Hong Kong Research Grants Council and in part by the Trans-Century Foundation for Outstanding Young Teachers sponsored by the National Education Ministry of China and a grant(No.1999043605)from the National 973 Projects o
文摘The time evolution of a two-dimensional line thermal-a turbulent flow produced by an initial element with significant buoyancy released in a large water body, is numerically studied with the two-equation k - epsilon model for turbulence closure. The numerical results show that the thermal is characterized by a vortex pair flow and a kidney shaped concentration structure with double peak maxima; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless time around 10. There are two regions in the flow field of a line thermal: a mixing region where the concentration of tracer fluid is high and the flow is turbulent and rotational with a pair of vortex eyes, and an ambient region where the concentration is zero and the flow is potential and well-described by a model of doublet with strength very close to those given by early experimental and analytical studies. The added virtual mass coefficient of the thermal motion is found to be approximately 1. The aspect ratio for the kidney-shaped sectional thermal is found to be around 1.45 for the self-similar phase. The predicted thermal spreading and mixing rate compares well with experimental data.
