Dynamic stall characteristics of a rotor airfoil under coupled pitching-plunging motions

The blade of a helicopter rotor encounters plunging motion in addition to periodic pitching oscillations during actual flight, which complicates the flow field structure and dynamic stall characteristics. The NACA 0015 rotor airfoil is selected as the study subject to examine the aerodynamic properties and stall mechanisms of multi-degree-of-freedom oscillations in a high-Reynolds-number rotor. The pitching-plunging coupled motion at a Reynolds number of 2.0×10⁶ is simulated using the Realizable k-ε turbulence model with a moving overset grid. Additional analysis is conducted on how the phase angle between pitching and plunging motions affects the dynamic stall characteristics.The results indicate that the downward motion is the primary phase during which the airfoil generates lift. Under high-Reynolds-number conditions, increasing the plunging amplitude to 150 mm allows the pure plunging motion to produce thrust. During upward movement, the airfoil encounters greater drag, raising the coupled motion's overall drag coefficient. The opposite effect is seen during the downward movement. At a phase angle of φ = π/2, the increase in the effective angle of attack (a combination of the pitching angle and the induced angle from the plunging motion) delays the lift stall angle by approximately 1°. However, the peak value of the drag coefficient increases by 56.9% compared with the pure pitching state.The plunging motion significantly impacts the development of the separation zone on the airfoil's upper surface, as well as the evolution and interaction of dynamic vortex structures across different scales and frequency domains. These effects result in differences in the aerodynamic force curves of the coupled motion and amplify the fluctuations during the negative pitch stroke. e curves of the coupled motion and amplify the fluctuations during the negative pitch stroke.