Direct effect of atmospheric turbulence on plume rise in a neutral atmosphere

Ashrafi, Khosro; Orkomi, Ali Ahmadi; Motlagh, Majid Shafipour

Direct effect of atmospheric turbulence on plume rise in a neutral atmosphere

2017

Ashrafi, Khosro | Orkomi, Ali Ahmadi | Motlagh, Majid Shafipour

The direct effect of atmospheric turbulence on plume rise in the current research work is studied through examining the turbulence intensity parameter. A hybrid unsteady Reynolds averaged Navier Stokes (RANS) and large eddy simulation (LES) numerical approach is applied with a new mixed scale sub-grid parameterization technique in the commercial ANSYS Fluent software in order to simulate the buoyant plume behavior in a turbulent crossflow. The accuracy of the simulation method is crosschecked against the wind tunnel data available in the literature. The numerical simulation results in various operating conditions are used to derive a new plume rise formula in which the direct effect of atmospheric turbulence intensity at stack height (IAir) is explicitly introduced in the plume rise formula. Furthermore, the buoyancy parameter of the flue gas is determined at some distances upstream of the stack top surface to include the whole effects of source buoyancy on the plume rise. The value of IAir at stack height is obtained by measuring the standard deviation of wind velocity at stack height. The sensitivity analysis showed that by increasing the atmospheric turbulence intensity, the final plume rise decreases because of the updraft and downdraft motions of turbulence and it has been found that there is a linear dependency between the plume rise and (IAir)−1.22. The quantile-quantile plots show that the new model can predict the simulated plume rise with a deviation factor of 1.0025 whereas the conventional models overestimate the final plume rise at least by a factor of 2.2.

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