New plume rise modeling in a turbulent atmosphere via hybrid RANS-LES numerical simulation

Abstract

New plume rise formulas are developed to overcome the drawbacks of the conventional models in predicting the rise of buoyant jets in different atmospheric stability conditions. A hybrid Reynolds averaged Navier Stokes (RANS) and large eddy simulation (LES) approach with a mixed scale sub-grid parameterization technique is applied. By using the aforementioned simulation results, new plume rise formulas are derived. The direct effects of atmospheric turbulence intensity at stack height (IAir) and the vertical derivative of wind velocity are introduced in plume rise formulas. The quantile-quantile plots show that new formulas can predict the simulated plume rise in the turbulent crossflow with a deviation factor of 1.18, 1.0025 and 1.17 for stable, neutral and unstable conditions, respectively whereas the conventional models overestimate the final plume rise at least by a factor of 6.1, 3.4 and 2.7. Moreover, by applying the new plume rise formulas in Gaussian dispersion model, the accuracy of new formulas is evaluated. The results show that by applying the new plume rise formulas instead of the conventional Briggs formulas in the Gaussian model, the normalized mean square error reduces by 20% and the fraction of predictions within a factor of two increases by 50%.