A method of reducing drag and fluctuating side force on bluff bodies

Abstract Measurements have been made of the forces imposed on typical two-dimensional bluff bodies with a small circular cylinder (here called a “rod”) placed upstream on the stagnation line. In most cases, the interaction was beneficial in that the drag of the overall system was lower with the rod than without it. Fluctuating side forces due to vortex shedding from the main body were also reduced for most rod positions and diameters. Three two-dimensional bluff bodies were investigated: a flat plate, a square and a circular cylinder. Reynolds numbers were in the range of 1 × 104 to 7 × 104. The measured overall drag coefficient at various rod spacing showed a discontinuous “jump” at some critical “jump” spacing. This change corresponded to the elimination of the usual single stagnation point on the bluff body centre line and the appearance of two stagnation points symmetrically placed, close to the lateral edges of the body. Significant drag reductions were obtained for all bluff body shapes when a front rod was located near the “jump” spacing. The fluctuating side force on the circular cylinder was reduced by the rod at high Re. On the square cylinder, the reduction in fluctuating side force was large (up to 90%) for any Re and rod size investigated.