Study of mechanisms and factors that influence the formation of vortical wake of a heaving airfoil

A two-dimensional numerical study is performed to investigate the relation between the direction of a deflected wake and the vortex pairing mechanisms. The deflection angle can be correlated with two effective phase velocities defined to represent the trends of symmetry breaking and symmetry holding, respectively. The deflection angle increases with the strength of the vortex pairs, which is associated with the heaving amplitude, frequency, and the free stream Reynolds number. Furthermore, not only the influence of Strouhal number but also those of the two heaving motion components - amplitude and frequency - are studied individually under different Reynolds numbers. The study shows that the deflection angle consistently increases with the difference between the symmetry-breaking phase velocity and symmetry-holding phase velocity.