•    When the Reynolds number exceeds to about 30, the two vortices are formed at the points of separation.

•    They rotate in opposite direction and elongate to such extent that they become unstable and are broken off form the body.

•    This process of formation of the vortices and their shedding away from the cylinder continues.



•    There are two rows of vortices formed moving downstream direction with very small velocity, these trails f vortices are commonly known as Karman vortex trails or street.

•    The absolute velocity of the vortices is equal to (V – V_v), then the parameter (U-U_v/ L), represents the frequency of shedding ‘f’.

•    The frequency ‘f’ with which vortices are shed form the cylinder is given by empirical formula.

f = 0.198 U/D [1-19.7/R_e]

f D/U = 0.198 ( 1- 19.7/R_e)

•    The parameter fD /U is known as strouhal number which is the function of Reynol’s number

Where,  U = Free stream velocity
               D = Diameter of cylinder
               U_v = Velocity of vortices formed

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