Aircraft vortex effects in forestry aerial spraying

Two previously developed codes have been integrated to simulate aerial spray dispersion over a forest. The integrated version of the model utilizes a second-order closure method to model aircraft vortex transport and dissipation, and a Lagrangian-based Markov chain technique to simulate the transport of spray droplets in a turbulent atmosphere. Droplet evaporation and impaction on coniferous needles are also included in the Lagrangian code.;Model predictions of deposit and drift within a distance of 400 metres downwind from the aircraft spray line are compared with measured data for two aircraft, the Ag-Truck Cessna-188 and the TBM Avenger.;A parametric analysis examining differences in the performance between the TBM and Ag-Truck, and the effect of aircraft height, windspeed at aircraft height, and atmospheric stability was performed. The results indicated very little difference between the TBM and the Ag-Truck. Percent deposit and drift within a 400 metre fetch were most sensitive to aircraft height, followed by windspeed at aircraft height and atmospheric stability.;An unstable atmosphere provided the optimum conditions for maximum canopy deposit (39%) and minimum drift (48%) in the simulation analysis.