Abstract
The behavior of drag and lift acting on a pair of circular cylinders arranged side by side near the critical Reynolds number were investigated in a low speed wind tunnel. When the gap between the cylinders is greater than about a cylinder diameter, the drag and lift of both cylinders are similar to each cylinder in variation respectively. The variations of drag and lift are similar to that of a single cylinder. The lift acts in the direction which two cylinders always repel each other. When the gap is smaller than about 1/2 diameters, the different variations of drag and lift between two cylinders are observed near the critical Re. When the gap is 1/4 diameters, one cylinder experiences negative lift and maximum drag near the critical Re. The negative lift is generated because the boundary layer transition occurs in the early stage on the surface of gap side of one cylinder compared with the outer side.
