NUMERICAL MODELING OF UNSTEADY FLOWS AROUND AIRFOILS BY A COUPLED POTENTIAL-BOUNDARY-LAYER METHOD

A numerical method, based on coupling a potential and a boundary-layer calculation, has been developed to predict unsteady airloads on airfo ils oscillating in 2D flows. An original feature of the numerical appr oach is in determining the geometry of the boundary at the junction be tween the two calculation domains, for flow zones corresponding to sep arated boundary-layer, and downstream of the trailing edge. The model is first shown to give good predictions of overall lift and drag coeff icients, for steady flows and angles of attack larger than the static stall angle of incidence. For pitching motions below dynamic stall, ca lculated lift values are also shown to match well with measured hyster esis loops. The influences of viscosity and of the geometry of the cou pling line are pointed out for such now cases. Dynamic stall calculati ons show the capabilities, and also the limits, of the proposed model: good agreement with experiments is obtained when a light dynamic stal l occurs, but the numerical model is less suitable to give a good pred iction of the behaviour of lift coefficient for deep dynamic stall cas es.