Implementation of a Simplified Micromixing Model Inside a Lagrangian Particle Dispersion Code for the Estimation of Concentration Variances and Peaks

In the frame of the modelling simulation of odour nuisances, the estimation of concentration peaks, representing values averaged over a relatively short time of the order of the interval between subsequent breathes, is of fundamental importance. Dispersion models currently used in this field cannot reconstruct this kind of values at relatively high frequency, due to their intrinsic theoretical design that allows to give time- or ensemble average concentrations only. The scope of this work is to describe the implementation of a simplified micromixing model inside a standard ensemble average Lagrangian Particle Dispersion Model, with the aim of simulating the field of concentration variances together with concentration averages. A simplified micromixing model represents a way to describe the interaction between the part of the emitted plume and the rest of the atmospheric flow, derived through bulk entrainment relationships. This simplified view allows the description of the first two moments of the concentration distribution which is however sufficient to describe a peak-to-mean relationship making some hypotheses about the form of the distribution. Some preliminary results of the application of this method inside the SPRAY Lagrangian Particle Dispersion Model are shown, comparing both the instantaneous concentration and the peak-to-mean ratio together with their spatial behaviour derived in some controlled conditions with those obtained from the application of other schemes currently included in the code