Three techniques to control flow separation in an S-shaped duct

Abstract

The optimum aerodynamic performance of an S-shaped duct (or, more specifically, aircraft air-intake duct) demands relatively uniform flow in the duct with minimal swirl at the exit. Here, three different flow control methods are examined for a large curvature S-shaped duct of uniform square cross section; they are vortex generators, variable directional tangential blowing, and vortex generator jets. The flow control devices were implemented on a common test rig with the same test parameters and hence provide a more accurate comparison of their performance. While these devices are effective at suppressing flow separation at the inside wall of the first bend and reducing total pressure loss, it is shown that this happens at the expense of higher swirl at the duct exit. The increase in the swirl can be attributed partly to the increase in the radial pressure difference (or imbalance) between the side walls and partly to changes in the configuration and position of streamwise vortices near the outside wall of the second bend. The investigation thus illustrates competing aerodynamic performance when flow control devices are implemented in an S-shaped duct. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc.