Wake structures behind plunging airfoils - A comparison of numerical and experimental results

Abstract

Comparisons are made between numerically and experimentally produced wake structures behind airfoils undergoing rapid, oscillatory plunging motions. Numerical simulations are performed using an unsteady panel code. Inviscid, incompressible ows about arbitrary moving airfoils are computed with the unsteady wake approximated by discrete point vortices, tracked using a Lagrangian mesh scheme. Numerically computed results are visualized using an interactive, graphical-animation interface. Experimental data are obtained from a low-speed water tunnel. Two-color dye injection is used to visualize unsteady wake structures, and velocity data are acquired using laser doppler velocimetry. Comparisons of vortex location agree well with linear theory for low amplitude motions. For large amplitude, high frequency motions, results diverge from linear theory, but wakes from the two approaches compare well with each other, including highly non-linear, non-symmetric wakes obtained for high amplitude, high frequency motions. Computed velocity pro les and integrated thrust coe cients for both approaches agree well.