Utilizing "bills" for drag reduction below transition on spherical bodies

Russian experimenters Kozlov and Leonenko have reported substantial drag reduction on a sphere using a "bill" or "spike" extending from the body upstream into the flow. A systematic series of experiments was conducted to determine the extent of the reduction and to identify the parameters of the reported drag reduction effect. The tests were performed in the Florida Atlantic University Ocean Engineering Department's Aerolab wind tunnel. A sphere was fitted with tapering bills of various lengths, base diameters, and bill/sphere fillet radii. Experiments indicated that the effect was restricted to Reynolds numbers below 4.0 x 10^5 and that the drag of the sphere/spike combination was actually increased at Reynolds numbers greater than this. A smoke generator was used to visualize the drag reduction mechanism, which appears to be a recirculating cell at the base of the sphere/spike intersection.