1 Proceedings of ICTACEM 2010 International Conference on Theoretical, Applied, Computational and Experimental Mechanics December 27-29, 2010, IIT Kharagpur, India ICTACEM-2010/148 Passive Flow Control through a Y-shaped Air Intake using Submerged Vortex Generators Akshoy Ranjan Paul * , Pritanshu Ranjan, Ravi Ranjan Upadhyay, Anuj Jain Department of Applied Mechanics, M. N. National Institute of Technology, Allahabad, India ABSTRACT Recent single-engine military aircrafts consists of a Y-shaped twin air-intake duct, which is mounted on either sides of the fuselage and carries atmospheric air into the compressor. Due to space constraint in aircraft design, such Y-duct diffusers may need to be curved to a great extent. To control the flow non-uniformity and total pressure distortion at the outlet of the duct, submerged vortex generators (SVG) are designed and are used at different locations inside the top and bottom walls of a Y-duct diffuser in multiple numbers. Such SVG produces micro-scale vortices, which transport high momentum fluid into the boundary layer, making it thinner and more resistant to the adverse pressure gradients with respect to flow separation. Two types of SVG are used: counter-rotating and co-rotating, depending upon the directions of vortices shedding into the downstream of flow in the Y-duct diffuser. Experimental data is obtained using five-hole pressure probe for the Y-shaped air intake duct and the same is used for CFD code validation. Parametric analysis of Y-ducts is then carried out by changing the geometrical parameters of SVG-1 (i.e., larger size SVG) with help of commercially available CFD code ‘Fluent 6.3’, which helps in finding out the optimum SVG design for Y-duct, for which total pressure distortion coefficient (DC 60 ) becomes lowest. The results show that for Y-duct with co-rotating SVG-2 mounted at the top and bottom sides at the inflexion plane exhibits over 16% decrease in total pressure distortion coefficient, whereas the same for counter-rotating SVG-2 accounts over 14% as compared to the Y-duct without any SVG. Besides, static pressure recovery coefficient with both types of SVG is increased by 2%, and total pressure loss coefficient is even reduced marginally. Deficit in momentum increases the chances of flow separation in Y-duct diffusers. A careful monitoring of momentum thickness helps to evaluate the delay in flow separation. The best configuration duct with SVG-2 in a co-rotating sequence records a highest reduction of momentum thickness (3.85%) as compared to the bare duct. Keywords: Flow control, Y-shaped air intake, Submerged vortex generators (SVG), Distortion coefficient, Computational fluid dynamics (CFD). 1. INTRODUCTION Twin-side air-intakes with a bifurcated Y-duct configuration are commonly used for ingesting atmospheric air to the engine of single-engine fighter aircrafts. Aircraft propulsion systems often use Y-shaped subsonic diffusing ducts as air-intakes. The main purpose of such Y-duct diffuser (Fig. 1) is to supply the ambient air from the fuselage mounted intake to the engine compressor (i.e., aerodynamic intake plane-AIP) for thrust generation. Due to space constraint in aircraft design, the diffusers may need to be curved to a great extent, which * Further author information: A.R.P.: E-mail: arpaul2k@yahoo.co.in, Telephone: +91 532 227 1219, Address: Department of Applied Mechanics, Motilal Nehru National Institute of Technology, Allahabad-211004, Uttar Pradesh, India.