Drag on a Group of Cylinders

An experimental investigation of the effects of spacing, orientation and Reynolds number on the drag of each cylinder in a group of two and three cylinders was carried out. The drag forces were measured by means of strain gages. The results indicate that the drag is strongly affected by mutual interaction with neighboring cylinders over a range of separation distances and angles of orientation with respect to the free-stream flow. The interaction decreases with increasing orientation angle, becoming very weak at θ = 90 deg when the cylinders are separated by at least two diameters. For spacings of approximately four diameters, the drag coefficients for the three-cylinder geometry reach a value which will remain almost constant for larger spacings. This is true for all three cylinders and for all orientations. The orientation of the cylinders influences only slightly the drag on the upstream cylinder for groups of both two and three cylinders. For downstream cylinders, the drag coefficient decreases with increasing Reynolds number due to the increased amount of unsteadiness contained in the flow behind the upstream cylinder.