Process of formation of a vortex street in the wake behind a flat plate

Abstract

The process of the formation of a vortex street in the wake behind a fla t pia te set parallel to a uni form flow was investigated in a low speed wind tunnel. The vorticity distributions in the wake were calculated from the measured velocities using Taylor's hypothesis.Just behind the plate, the equi-vorticity lines were nearly parallel to the free stream. At locations somewhat downstream, sinusoidal contour lines appeared near the wake center. Further downstream. some closed contour lines appeared in the figures mapped. The arrangement of the closed lines suggests the existence of a vortex street. The maximum value for vorticity in a wave length of the fundamental velocity fluctuation decreased in the downstream direction; the concentration of vorticity, however, increased in a region the further downstream it was. Meanwhile, the value for circulation obtained by the surface integral of vorticity within the closed contours of a vortex increased until the vortex street was estahlished.

Onset of nonlinearity in a two-dimensional thin shear layer

“…For instance, in the symmetrical wake behind a flat plate, a sufficiently amplified fluctuation due to the inflection point instability produces harmonic components, generating an antisymmetrical double vortex street known as the Kármán vortex street (Sato and Kuriki 1961, Sato 1970, Sato and Saito 1975. This configuration remains until threedimensional distortion occurs in the further downstream Kuriki 1961, Okude andMatsui 1988). In contrast, harmonics and subharmonics emerge in the asymmetrical mixing layer behind a splitter plate (Sato 1959, Miksad 1973, Hajj et al 1992.…”