The unsteady aerodynamics of a wing in the wake of a periodically plunging upstream airfoil was investigated in water tunnel experiments. By varying the frequency and the amplitude of the plunge oscillations, vortex-street configurations with varying wavelength and circulation were generated. Depending on the angle of attack of the wing, the largest lift force is found when the leading edge of the wing is located at the wake centerline or just above it. Flow separation at the leading edge, formation of a leading-edge vortex, and coupling with incident vortices are observed with increasing angle of attack. The lift time history has higher harmonics up to $n=5$ when the wing is close to the wake centerline. This is due to the cross-stream velocity profile in the undisturbed wake and can be also predicted by a point-vortex model. The peak lift coefficients decrease with increasing deflection angle of the wake if the upstream airfoil is plunged at nonzero mean angle of attack. This occurs as the geometry and circulations of the vortices in the reversed Karman vortex street are modified. For the unloaded wing in the symmetric wakes, the peak lift coefficients increase with increasing frequency and amplitude of the plunging airfoil. These kinematic parameters also determine the amplitude and shape of the cross-stream velocity profiles and the degree of two dimensionality in the undisturbed wake. The amplitude of the lift coefficient of the wing depends on a single wake parameter, which is the Strouhal number based on the amplitude of the upstream airfoil.

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• Aerodynamics
• Vortex flows
• Wakes & jets