THE EFFECT OF FREE-STREAM TURBULENCE ON SECTIONAL LIFT FORCES ON A CIRCULAR-CYLINDER

Wind-tunnel experiments were conducted to examine the effect of grid-g enerated turbulence on lift forces at sections of a circular cylinder. Turbulence of longitudinal intensity between 0.6% and 18% was employe d, with cylinder Reynolds numbers in the range 1 x 10(5) to 5 x 10(5). Addition of low-intensity turbulence had the primary effect of induci ng the critical transition at Reynolds numbers below that for smooth f low; above transition there was little difference between the forces e xperienced by the cylinder in smooth or turbulent flow, with no sign o f organized vortex shedding. At higher turbulence intensities effects consistent with a return to organized vortex shedding were observed, p articularly for the highest intensity and at the upper end of the Reyn olds number range; lift coefficients were greater than in smooth super critical flow, with a broad spectral peak centred near a Strouhal numb er of 0.23 accompanied by an increase in spanwise correlation lengths of lift force.