Experimental investigation of the sensitivity to in-line motions and magnus-like lift production on the vortex-induced vibrations

Experiments were carried out with a transversely oscillating cylinder in steady current, to investigate the sensitivity to small cylinder pitch rotations and in-line motions on the vortexinduced lift forces. The in-line motions of a spring blade mounted cylinder are convex when towing forward (pushing) and concave when towing backwards (pulling). At the same time the cylinder performs a small pitch rotation (about its central axis), which could induce Magnus-like lift forces. An unexpectedly large sensitivity was found to the in-line motions in certain tests with oscillation amplitudes of over half a diameter. The observed sensitivity to the cylinder pitch rotations was rather small. The tests were carried out in the lock-in regime for VIV and at sub-critical Reynolds numbers, which are close to the critical Reynolds regime. The results presented in this paper will initiate further investigation and will potentially have practical implications as well.

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