On the force signatures of a pair of multi-plunging airfoils

The unsteady aerodynamics of a pair of multi-plunging airfoils is studied using computational fluid dynamics based on a finite volume method and dynamic layering mesh motion algorithm. The two-dimensional unsteady, incompressible Navier–Stokes equations are used as the governing equations while the thin ellipsoidal airfoils, commonly used in micro aerial vehicles, perform harmonic plunging motion. The instantaneous lift and drag coefficients are examined in detail and the effects of Reynolds number, frequency and amplitude of oscillations, and the airfoils’ centre-to-centre spacing on the force coefficients are investigated. It is shown that the force coefficients of each of the plunging airfoils differ noticeably from those of a single plunging airfoil both quantitatively and qualitatively, showing the significance of the airfoil–airfoil interaction. It is also observed that the investigated parameters affect the magnitude and characteristics of the real-time lift and drag coefficients. There is an optimum frequency of oscillations, resulting in the highest thrust generation between the investigated frequencies. The amplitude of oscillations increases the aerodynamic performance by increasing the mean lift coefficient but decreasing the mean drag coefficient at the same time. Re effects on the lift coefficient are negligible; however, it is shown that increasing Re causes the airfoils to generate more thrust compared to the lower Re investigated here.