DYNAMIC STALL AND WAKE EFFECTS ON TRIM AND STABILITY OF HINGELESS ROTORS WITH EXPERIMENTAL CORRELATION

This paper investigates the effects of dynamic: stall and three-dimens ional wake on trim (control inputs and periodic responses) and lag dam ping of isolated hingeless rotors, The ONERA dynamic stall models of L ift, drag and pitching moment and a finite-state three-dimensional wak e model are used, The investigation covers three items: (1) a converge nce study of trim and lag damping with respect to the number of wake h armonics and shape functions under dynamically stalled conditions; (2) a parametric study of periodic response and lag damping for varying a dvance ratios; and (3) a comprehensive correlation with the measured l ag-regressive-mode damping of a three-bladed rotor operated untrimmed, The correlation Includes near-zero thrust conditions in hover and for ward flight to high-thrust and highly stalled conditions in forward fl ight with advance ratio as high as 0.55 and shaft angle as high as 20 degrees, The convergence and parametric studies are based on a three-b laded isolated rotor in propulsive trim; the cantilever blades have fl ap bending, lag bending and torsional degrees of freedom with a quasis teady treatment of axial deformation, The trim and the Floquet transit ion matrix (FTM) about that trim am obtained by periodic shooting with the fast Floquet theory and damped Newton iteration, and the damping levels and modal frequencies are obtained from the eigenvalues and eig envectors of the FTM. All the structural and aerodynamic states are in cluded in both trim and damping predictions, Dynamic stall and wake ap preciably affect these predictions and, overall, improve the correlati on.