CALCULATION OF DYNAMIC STALL BY VISCOUS-INVISCID INTERACTION OVER AIRFOILS AND HELICOPTER-BLADE SECTIONS

A time-consistent new extension of a viscous-inviscid interaction method for stalled airfoils has been developed. The deep dynamic stall over airfoils at high angles of attack is calculated. An hybrid integral/local thin-layer method is used for the viscous flow, and the unsteady full potential equation for the inviscid flow. The Le Balleur’s “Semi-inverse” coupling algorithm, in its “Massive-separation” 2D-steady form, is converged at each time step and reaches a time-consistent coupling. This gives the correct access to compute the unsteady and massively separated flows which are characteristic of deep dynamic stall. Numerical results of highly separated unsteady flows are first presented in the case of the NACA0012 airfoil in pitch oscillation, at subsonic speed and high Reynolds number. Two-dimensional simulations of light as well as deep dynamic stall over a blade section of helicopter in forward flight, taking into account the full motion of the rotor, are also presented. The satisfactory agreement between theory and experimental data demonstrates that the method reproduces the major features of the dynamic stall process, and that a practical prediction tool is obtained for this complex fluid dynamic phenomenon.