Vortex Load Reduction: Experiments in Optimal Helical Strake Geometry for Rigid Cylinders

Abstract

Vortex-induced lift loads and their energy spectra were measured on laboratory-scale models of isolated, rigid, right circular cylinders subjected to steady, transverse currents. The control cylinder was smooth and the others were fitted with right-handed or left-handed, constant angle helical strakes that protruded one-tenth the cylinder diameter. For Reynolds numbers of the order of 104 , the results clearly show that, compared with the smooth cylinder counterpart, the geometry that most effectively reduces both the lift coefficient and also the peaks of the lift load energy spectra in the low frequency band is three evenly spaced strakes at a 60-deg angle with the cylinder’s transverse axis.