The paper presented the specifics of calculating the characteristics of vortex propagation and decay processes which cause aerodynamic tail fin-buffet loads in an aircraft at incompressible subsonic flow. Analysis of numerical diffusion and stability of differencing schemes implemented in OpenFOAM software package has been carried out. Based on the obtained results, differencing schemes are selected and their modification has been done. An algorithm has been presented for combining various approaches for modelling turbulent flows (RANS-LES) by means of zonal isolation and its implementation in OpenFOAM package is carried out. A series of calculations of three-dimensional flow around an aircraft at angles of attack of 0 to 30 degree considering airbrake deflections on 60 degree are conducted. Flow separation at the airbrake side edges and upper edge result in a highly turbulent wake. The corresponding region of vortex flow affects the fin and causes buffet loads.