Wind Load on Cylinder with Spanwise Protrusion

Drag and lift forces for circular cylindrical bodies with two types of spanwise protrusions were measured in a wind tunnel in the transition range of Reynolds numbers (10⁴ to 10⁵), with the protrusion size varying from 0.004 to 0.006 of the cylinder diameter. The data show that the two protuberance shapes, a trip-wire and an overlap, are nearly identical in their effect on the aerodynamic characteristics, and that their effect depends much more on location than on size. It was found that the drag coefficient could vary by ±40% and that the lift coefficient could be as high as 0.7, depending on the location of the protuberance, or equivalently on the angle of attack. By using hot-wire anemometry to study the flow field, these significant variations in C_D and C_L were revealed to be associated with fundamental changes in the boundary-layer flow, caused by the interaction of the protrusion with the surrounding fluid motion.