Analysis and computation of the cross-flow past an oscillatiang cylinder with two degrees of freedom

Al-Mdallal, Qasem M. (2004) Analysis and computation of the cross-flow past an oscillatiang cylinder with two degrees of freedom. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The present thesis deals with analysis and numerical simulation of a new class of wake flows created by combined recti-linear (translational) and rotational oscillation of a cylinder placed in a steady uniform flow. The flow is incompressible and two-dimensional, and recti-linear and rotational oscillations are harmonic. The instantaneous translation and rotation start at the same moment and the development of the flow is studied in a coordinate frame which moves with the cylinder but does not rotate. The analysis is carried out for combined phase-locked translation and rotation with a single frequency. The results are presented for five set of the four dimensionless groups which characterize this flow. The resulting vortex formation modes and synchronization (lock-on) phenomena behind the cylinder (in the near-wake region) as well as the fluid forces acting on the cylinder are analyzed. In addition, a series of one-degree-of-freedom (1-DoF) forced vibration calculations are carried out to better understand what differences result from the addition of rotational oscillations to streamwise (in-line) or cross-stream (transverse) motion and to see which effects a transverse-only or in-line-only simulations miss. The numerical scheme is verified by applying it to the special cases of uniform flow past a stationary cylinder; a steadily rotating cylinder; a cylinder undergoing (1-DoF) forced (recti-linear or rotational) oscillations. Exceptionally good comparisons with previous experimental and numerical results are obtained. Furthermore, the simulations of the start-up flow for the case of combined (2-DoF) forced recti-linear and rotational cylinder oscillations at a moderate Reynolds number are consistent with the results of the analytical solution.

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