Buoyant plume rise described by a Lagrangian turbulence model

A Lagrangian turbulence model is presented, which describes buoyant turbule nce fully consistent with Eulerian budget equations as motion of fluid part icles and change of their temperatures. This model is applied to the descri ption of buoyant plume rise. Due to the simulation the turbulent mixing pro cesses between the plume and ambient fluid in dependence on varying ambient conditions, the plume rise model presented here offers different advantage s in comparison to existing models: the different plume rise phases are cal culated consistently and the full plume statistics is obtained. The model p redictions are compared to consequences of the similarity theory, results o f large-eddy simulations and lidar measurements of the plume height and wid th in the atmosphere. For different hows with varying shear and stratificat ion, we find in all these comparisons a good agreement between our computat ions and measurements, simulations and theoretical predictions. In particul ar, it is shown that the similarity theory appears as a special case of the theory presented here. The simplicity and the low computational costs of o ur model make it well-suited for routine applications. (C) 1999 Elsevier Sc ience Ltd. All right reserved.