Studying the wake contraction of the flow-field of a rotor in hover

This article presents a comparative study of three numerical algorithms for computation of the flow-field of a rotor in hover and the net static thrust that is produced. The flow-field is induced by a series of vortex rings, modelling the near wake of the hovering rotor and a single semi-infinite vortex cylinder, accounting for the velocity deficit in the far wake. All three models are based on the vortex theory and differ in the choice of the numerical scheme for the estimation of the exact position of the vortex rings, emitted at the tips of the blades of the rotor. Thus, the numerical models perform a real-time simulation of the propagation of the vortex rings in the downwash. The first model uses an Euler-predictor scheme, while the second and third models use respectively first and second order predictor-corrector schemes. The aim of the study is to assess the rapidity and accuracy of each algorithm. For that purpose, the numerical results are compared with the experimental data, obtained from a wind tunnel test of the model rotor. The best results in terms of computational speed and accuracy are obtained with the use of Adams-Bashforth predictor-corrector scheme of second order