A METHOD FOR THE REDUCTION OF BLUFF-BODY DRAG

Although several techniques for the reduction of bluff body drag have been proposed in the literature by previous investigators, most of the se investigations did not estimate the drag of the entire system consi sting of bluff body and drag-reducing device. In the present study, we have devised a method of not only reducing the drag of the bluff body , but reducing the drag of the entire system to values well below that of the bluff body alone. Our method, which utilizes a small flat plat e placed upstream of and parallel to the cylinder (with the plate orie nted normal to the free stream): has yielded an optimal geometrical co nfiguration consisting of a plate height one-third the cylinder diamet er placed 1.5 diameters upstream of the cylinder, and produces a syste m drag that is 38% that of the bare cylinder alone. The reduction in d rag is manifested through two distinct modes of the flow - a cavity mo de observed for small values of the plate-cylinder gap, and a wake-imp ingement mode observed for larger values of this gap. The cavity mode is found to deliver a larger reduction in drag due to a substantial in crease in thrust associated with the front surface of the cylinder.