A 3D Lagrangian micromixing dispersion model LAGFLUM and its validation with a wind tunnel experiment

A stochastic numerical model, LAGFLUM (LAGrangian FLUctuation Model), is developed to determine the mean and the fluctuation statistics of scalar fields generated in 3D turbulent flows from continuous sources. The model couples a macromixing scheme with a micromixing scheme. The macromixing scheme, based on the so called “well-mixed” criterion, is utilized to evaluate the mean concentration, while the micromixing IECM (Interaction by Exchange with the Conditional Mean) scheme is integrated to calculate the higher statistical moments of the concentration. The model LAGFLUM is tested by comparison with the MUST (Mock Urban Setting Test) wind tunnel experiment, which is the laboratory counterpart of the original (real-atmosphere) MUST experiment. In both these experiments the dispersion of a passive tracer in a 3D flow field, in the presence of obstacles, is measured. Using a flow field reconstructed from the experimental flow measurements, the ensemble mean, standard deviation, intensity of fluctuations and skewness of the concentration predicted by LAGFLUM are compared with the available measurements. The results show a generally good agreement between the observations and the simulation, in particular for the mean and the standard deviation of the concentration. Predictions obtained with the flow field replaced by a flow field calculated using a numerical model and with the IECM model replaced by the IEM (Interaction by Exchange with the Mean) model are also compared with the measurements.

► A 3D Lagrangian model is developed to determine the concentration fluctuations.
► The model is tested by comparison with the MUST wind tunnel experiment.
► The micromixing IECM scheme is coupled with a macromixing scheme.
► The concentration variances agree well with observations.