Efficient measurement of hydrodynamic coefficients for vibrating cylinders at supercritical Reynolds numbers

Free-response Vortex-Induced Vibration (VIV) tests were conducted on a 6.233 m long cylinder with a diameter of 0.325 m. The cylinder was allowed to vibrate in the cross flow direction and towed at Reynolds numbers varying from 200,000 to 700,000. Rather than conducting hundreds of individual tests at discrete values of reduced velocity, the free-response was measured while continuously varying the towing speed in a manner that ensures quasi-steady response. These 'ramp-tests' not only yielded response data corresponding to continuously varying reduced velocity, but also yielded observations of the hysteresis effects associated with increasing or decreasing flow speed. The results from the carefully conducted 'ramp-tests' are compared with steady towing speed results to confirm their validity. The cylinder's free-response was controlled by systematically varying the external electro-mechanical damping. Lift and added mass coefficients at supercritical Reynolds numbers were extracted using the known relationships between cylinder response and hydrodynamic loading. Contour plots of lift and added mass coefficients are presented as a function of dimensionless response amplitude and reduced velocity. Stationary cylinder drag coefficients were also efficiently acquired using the ramp testing technique. These results are presented and compared with the VIV amplified drag coefficients. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

Free-response Vortex-Induced Vibration (VIV) tests were conducted on a cylindrical structure to study its response and hysteresis effects. By continuously varying the towing speed using a ramp-testing technique, the response data corresponding to continuously varying reduced velocity were obtained. The external electro-mechanical damping was systematically varied to control the cylinder's free-response and extract the lift and added mass coefficients. Contour plots of these coefficients as a function of dimensionless response amplitude and reduced velocity were presented. The drag coefficients of the stationary cylinder were also efficiently acquired using the ramp testing technique and compared with the VIV amplified drag coefficients.