This work aims at introducing model methodology and numerical studies related to a {Lagrangian} stochastic approach applied to the computation of the wind circulation around mills. We adapt the Lagrangian \textit{stochastic downscaling method} that we have introduced in [3] and [4] to the atmospheric boundary layer and we introduce here a Lagrangian version of the \textit{actuator disc} methods to take account of the mills. We present our numerical method and numerical experiments in the case of non rotating and rotating actuator disc models. First, for validation purpose we compare some numerical experiments against wind tunnel measurements. Second we perform some numerical experiments at the atmospheric scale and present some features of our numerical method, in particular the computation of the probability distribution of the wind in the wake zone, as a byproduct of the fluid particle model and the associated PDF method.