Dispersion of a Passive Scalar Fluctuating Plume in a Turbulent Boundary Layer. Part III: Stochastic Modelling

International audience; We analyze the reliability of the Lagrangian stochastic micromixing 8 method in predicting higher-order statistics of the passive scalar concentration in-9 duced by an elevated source (of varying diameter) placed in a turbulent boundary 10 layer. To that purpose we analyze two different modelling approaches by testing 11 their results against the wind-tunnel measurements discussed in Part I (Nironi 12 et al., Boundary-Layer Meteorology, 2015, Vol.156, 415-446). The first is a prob-13 ability density function (PDF) micromixing model that simulates the effects of 14 the molecular diffusivity on the concentration fluctuations by taking into account 15 the background particles. The second is a new model, named VPΓ , conceived in 16 order to minimize the computational costs. This is based on the volumetric par-17 ticle approach providing estimates of the first two concentration moments with 18 no need for the simulation of the background particles. In this second approach, 19 higher-order moments are computed based on the estimates of these two moments 20 and under the assumption that the concentration PDF is a Gamma distribution. 21 The comparisons concern the spatial distribution of the first four moments of the 22 concentration and the evolution of the PDF along the plume centreline. The nov-23 elty of this work is twofold: i) we perform a systematic comparison of the results 24 of micro-mixing Lagrangian models against experiments providing profiles of the 25 first four moments of the concentration within an inhomogeneous and anisotropic 26 turbulent flow, and ii) we show the reliability of the VPΓ model as an operational 27 tool for the prediction of the PDF of the concentration. 28