Modelling of Aerodynamic Interactions in Compound Helicopters

Carlos Santos

Key information

Authors:

Carlos Santos (Carlos Santos Sousa)

Supervisors:

Filipe Szolnoky Ramos Pinto Cunha (Filipe Szolnoky Ramos Pinto Cunha)

Published in

12/09/2010

Abstract

The prediction of aerodynamic interactions has been shown to earn careful consideration in helicopter design because of their consequences to the handling qualities, dynamics and performance. Under forward flight condition at moderate advance ratio, aerodynamic interactions may manifest as high levels of vibration and noise or as large nose-up pitching moments acting on the helicopter. These effects are investigated in a generic coaxial helicopter that is representative of modern configurations and features a hingeless hub, rigid blades and thrust compounding. The correct prediction of the detailed evolution of the vortex structures within the helicopter rotor wake is essential for the analysis of aerodynamic interactions. This is properly addressed by using lifting-line theory coupled to a Vorticity Transport Model to compute the evolution of the vorticity generated at the rotor blades. This finite volume boundary-free model solves the vorticity equation and circumvents the excessive numerical diffusion of vorticity that limits standard CFD-based techniques. Numerical simulations on several combinations of the components that constitute the helicopter were carried out and compared against the results for the full helicopter in order to better understand the origins and effects of the interactional phenomena. It is shown that the effects of some aerodynamic interactions can be directly ascribed to a particular event, like the impingement of the main rotor wake into another component, while others may manifest in a more subtle way, like the mutual interaction between the wakes generated by different rotors or the displacement of the main rotor wake caused by the airframe.