Influence of cross-sectional configuration on the synchronization of Karman vortex shedding with the cylinder oscillation

The influence of cross-sectional configuration of a cylindrical body on the lock-in phenomenon of Karman vortex shedding was investigated using a mechanical oscillator for cross-flow oscillation of the cylinder. A circular, a semi-circular and a triangular cylinder with an equal height were used as test cylinders to see the effect of the movement of the separation point. The lock-in criteria accounting for the spanwise coherency of the Karman vortex were discussed based on the experimental data under a fixed Reynolds number of around 3 500. The lock-in region on the plane of non-dimensional cylinder frequency and the non-dimensional amplitude was almost the same for all of the cylinders in spite of differences in the range of the separation point movement. The minimum value of non-dimensional threshold amplitude for lock-in was much smaller than the value of 0.05 which was reported so far. Results obtained in this work imply that the movement of the separation point is a result of the lock-in phenomenon, rather than an essential cause.