Abstract: Disclosed are methods and apparatus for effecting a selected pattern of fluid flow wherein a first fluid is caused to flow along the surface of a body and a second fluid is caused to flow out of a plurality of holes in the surface of the body. The holes are arranged in a pattern so that the flow of the second fluid creates a baffle to change the direction of flow of the first fluid. The pattern is a grouping of holes wherein the grouping may be a straight line or a helix around a tubular body. The holes are rectangular in cross-section to form a fan-shaped pattern in the fluid passing through the holes. The longitudinal axis of each hole does not intersect the center of adjacent holes.