The Effects of Vortex Coherence,Spacing,and Circulation on the Flow-Induced Forces on Vibrating Cables and Bluff Structures.

摘要

The vortex wake of a vibrating flexible cable was studied by means of velocity measurements and correlation, frequency spectra, and flow visualization. Three distinct spanwise regimes were identified according to wake structure. Near the cable nodes the flow resembles that of a stationary cable. Adjacent to the node is a transition regime which extends up to the locked-in or synchronized wake flow about the cable antinode. Each regime was characterized by spectral content, degree of spanwise correlation, and local vortex street geometry. Measured downstream velocity profiles and vortex spacing were matched with a mathematical model to obtain the vortex strength and its relation to cable vibration conditions. The von Karman drag formula was used to compute the steady drag coefficients directly, and the distributions of fluctuating lift and drag were inferred from the data. The vortex strength and fluid forces on the vibrating cable were found to be as much as 65 percent larger for locked-in conditions than in the stationary case. Where comparisons were possible, there was good agreement between present results and previous results for vortex-excited rigid cylinders, including some direct measurements of the increased drag. (Author)