Effect of frequency ratio on the force coefficients of a cylinder oscillated in a uniform stream

Baranyi, László (2008) Effect of frequency ratio on the force coefficients of a cylinder oscillated in a uniform stream. In: 7th JSME-KSME Thermal and Fluids Engineering Conference, 2008.10.13-2008.10.16, Sapporo.

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Abstract

A finite difference solution is presented for 2D low Reynolds number flow around a circular cylinder placed in a uniform flow. The cylinder is oscillated in-line or transversely or is moved along an elliptical path. Abrupt jumps between two state curves were found in the time-mean (TM) and root-mean-square (rms) values of the force coefficients under lock-in conditions when plotted against frequency ratio. For orbital cylinder motion, jumps were found at certain frequency ratio values in the TM and rms values of all force coefficients and number and location of jumps were identical for all coefficients, similar to previous results plotted against ellipticity. When the cylinder was oscillated in-line, sudden changes were found only for the TM of lift and torque coefficients. However, when the cylinder was oscillated in transverse direction only, none of the TM and rms curves showed any jumps. Pre- and post-jump analysis (flow patterns, limit cycle curves) revealed switches in vortex structure.

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