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vortex street[′vȯr‚teks ‚strēt]
a system of sequential vortices that form in a fluid during flow around long cylindrical bodies whose axis is perpendicular to the direction of movement. The vortices break off alternately from the sides of the body, and they arrange themselves in checkerboard order in the form of two chains behind the body. The vortices of one chain rotate clockwise, and those of the other chain rotate counterclock-wise. Vortex streets are unstable and may be clearly ob-served only at small Reynolds numbers Re. In addition, a fixed ratio has been observed between the width h of a vortex street and the distance l between the adjacent vortices of each row: h/I = 0.281. Experiments have demonstrated that the size of the vortex street also depends on the size of the streamlined body.
Energy is expended in the formation of vortices; therefore the body behind which the vortex street originates experiences drag. The resistance of the body decreases with a de-crease in the width of the vortex street.