Experimental investigation on the flow around single and tandem cylinder configurations at Reynolds numbers from 40.000 up to 12 million

Abstract

Steady and unsteady force measurements and surface pressure measurements on cylinders in single and tandem configurations were performed for Reynolds numbers from sub- up to transcritical values. The smooth and rough cylinders, either with a square cross-section and rounded edges or with a circular cross-section, represent typical column shapes for large floating offshore structures. The measurements were conducted in the DNW High Pressure Wind Tunnel in Göttingen, a specialized high Reynolds number facility. The aerodynamic forces on the cylinder were measured using a both sided piezo-electric balance. For the tandem cases, only the forces on the downstream cylinder were measured due to restrictions of the test setup. In addition to the unsteady force measurements the time-mean surface pressures at two locations on the cylinders were obtained. As a supplement, a pressure rake was used to measure the time-mean pressure and thus velocity distribution in the wake of the (downstream) cylinder. Variations of the Reynolds number were possible over almost three orders of magnitude in the range from Re = 4·10^4 up to 12·10^6 by changing the free stream flow velocity and the total pressure. In case of the square cross-section cylinders the dependence of the aerodynamic forces and surface pressures on the Reynolds number were investigated for various angles of incidence � and for two non-dimension surface roughness values of O(10^−6) and O(10^−3). At the maximum angle of incidence the blockage did not exceed 13%. For the tandem configurations the distance between the centers of the cylinders had a value of 4.0 and 5.6 times the diameter for the square cylinders and of 2.8 and 4.0 times the diameter for the circular cylinders. For all configurations drastic changes of the global values as function of the Reynolds number were observed.