Influence of Secondary Flow on Drag Force

An experimental investigation was made to determine the axial variation of drag on a finite length circular cylinder with end plates and immersed in a linear velocity gradient flow. The drag coefficient for an incremental length of cylinder was found to vary from a minimum where the velocity was greatest to a maximum where the velocity was least. The force acting over the full cylinder length was found to be greater than that calculated for a uniform flow at the average velocity over the cylinder length. The pressure coefficient was found to differ when measured at the same velocity both in a uniform flow and a linear velocity gradient flow, a difference explained by secondary flow generated by the stagnation pressure gradient on the leading edge of the cylinder. A drag coefficient parameter was defined and found to increase uniformly as the length-to-diameter ratio, L/d, increased to a value of about seven; past this value the drag coefficient parameter was found to decrease.