Control of Flow Separation in S-ducts via Flow Injection and Suction Marco Debiasi 1 , Marco Robert Herberg 2 , Zeng Yan 3 , Shyam Sundar Dhanabalan 4 , and Her Mann Tsai 5 Temasek Laboratories, National University of Singapore, Singapore, 117508, Singapore This work explores the use of injection and suction as a mean to control the separation of flow in S-duct inlets. The overall goal is to reduce the distortion of the S-duct outlet flow and to improve its pressure recovery by using the least expenditure of energy. We also aim to understand to what extent computational means can be practically useful for optimizing this flow-control method. Computations and experiments were used to study the effect of injection and suction of 2% on the main stream in an S-duct of M2129 geometry. The control flow can be recirculated with advantages in term of mass flow and energy management. The benefit of the method is assessed by contrasting controlled flows to corresponding baseline (no-control) flows over a range of subsonic inlet conditions. The experimental measurements substantially validate the results from computation and indicate that the method is highly effective in controlling the flow separation. Nomenclature C p = static pressure coefficient = ( ) 2 2 1 i i i U p p ρ − D = diameter of S-duct l = length of S-duct centerline m & = mass flow rate M = Mach number p = static pressure p 0 = total pressure PR = total to ambient pressure ratio at the S-duct inlet Re D = Reynolds number based on the diameter s = S-duct centerline coordinate T = static temperature T 0 = total temperature U = flow velocity ρ = flow density ζ = azimuthal angle Subscripts i = conditions at the S-duct inlet o = conditions at the S-duct outlet ∞ = ambient conditions I. Introduction HE inlets of aircraft turbines are designed to decelerate the freestream while achieving a uniform flow distribution with minimum stagnation pressure losses at the compressor face. In some aircraft a straight inlet T 1 Research Scientist, Temasek Laboratories, National University of Singapore, Singapore, Member AIAA. 2 Associate Scientist, Temasek Laboratories, National University of Singapore, Singapore. 3 Research Scientist, Temasek Laboratories, National University of Singapore, Singapore. 4 Associate Scientist, Temasek Laboratories, National University of Singapore, Singapore. 5 Senior Research Scientist, Temasek Laboratories, National University of Singapore, Singapore, Member AIAA. American Institute of Aeronautics and Astronautics 1 46th AIAA Aerospace Sciences Meeting and Exhibit 7 - 10 January 2008, Reno, Nevada AIAA 2008-74 Copyright © 2008 by Temasek Laboratories - National University of Singapore. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.