Apparatus for reducing dissipation rate of fluid ejected into boundary layer

Injection of additives such as microbubbles or high molecular weight materials such as polymers into the boundary layer of a fluid flow has been shown to reduce skin friction drag significantly for both vessels moving relative to water and for pipeline applications. The microbubbles or large polymer molecules interact with the turbulent activity in the near-wall region, absorbing energy and reducing the frequency of burst (high energy fluid moving away from the wall) and sweep (low energy fluid replacing the high energy fluid in the near-wall region) cycles. The reduced burst frequency results in less energy dissipation from the wall and can result in skin friction drag reductions up to 80%. Experiments have shown that the efficacy of polymer molecules for drag reduction is closely related to their molecular weight, their location in the boundary layer, and the degree to which they have been unwound, aligned, and stretched (i.e., "conditioned"). A method and apparatus for ejecting a second fluid into the near-wall region of the boundary layer of a first fluid, so that the second fluid hugs the wall. This alone reduces drag by modifying the behavior of the near-wall structure, thereby reducing the frequency of burst and sweep cycles, even when the first and second fluids are identical. Further, one or more additives, such as polymer, surfactant, micro-bubbles, a combination thereof, and/or using a second fluid having an elevated temperature as compared to the temperature of the first fluid, may be used to achieve much greater drag reduction as well as lower dissipation rates than previously possible. The second fluid is ejected using a convex Coanda surface () and at a controlled velocity that is a small fraction of the velocity of the first fluid moving along the wall so that the flow lines of the second fluid are substantially aligned with the flow lines of the first fluid. To make the second fluid continue to hug the wall after ejection, vortices are generated in the second fluid by a concave surface () so that low pressure regions exist at the wall.