Effect of angle-of-turn on the performance of divided intake ducts S Bharani 1 , S N Singh 2 * , V Seshadri 2 and R Chandramouli 2 1 Department of Mechanical, Materials and Aerospace Engineering, University of Central Florida, Orlando, Florida, USA 2 Department of Applied Mechanics, Indian Institute of Technology Delhi, New Delhi, India Abstract: Investigations using computational ¯uid dynamics (CFD) have been carried out on divided intake ducts having angles-of-turn as 22.58/22.58, 308/308 and 458/458 and area ratios of 2 and 3. It is observed that the core ¯ow in the duct remains towards the convex walls up to the outlet plane with lower magnitudes in the centre of plane. Cross-velocity magnitudes are found to be less than 10 per cent of the longitudinal velocity at the outlet plane. Pressure recovery is found to decrease with the increase in the angle-of-turn for both area ratios. Keywords: divided intake duct, angle-of-turn, area ratio, velocity distribution, pressure recovery NOTATION AR area ratio C pr static pressure recovery coef®cient ˆ 2…P ex ¡ P in †=…ru 2 † C L total pressure loss coef®cient ˆ 2…P T in ¡ P T ex †/…ru 2 † D inlet diameter L s duct length L 0 distance between two inlet ducts L 1 /L percentage of centre-line arc length P ex exit static pressure (average) P in inlet static pressure (average) P T ex exit total pressure (average) P T in inlet total pressure (average) R c radius of curvature u mean velocity y angle-of-turn 1 INTRODUCTION The intake of a ®ghter aircraft must meet the engine mass ¯ow demand in a steady and symmetric manner over a wide range of aircraft speeds and altitudes [1] with higher static pressure recovery and low distortion. Divided intake ducts are widely used for ingestion of atmospheric air to the single-engined ®ghter aircraft. These offer great ¯exibility to diffuse the incoming air over a short duct length and hence with a smaller pressure drop due to skin friction. The intakes are normally side-mounted and the two limbs of the duct merge inside the fuselage into one and feed air at the compressor face at a Mach number in the range 0.3±0.5 with minimum turbulence. The offset positioning of the intakes with respect to the engine leads to a dif®cult design problem to tailor the S-shaped ducts to conform to constraints imposed by other aspects of the aircraft design. Martin and Holzhauser [2] observed that as the intake mean ¯ow ratio is reduced by some form of exit control, a critical point is reached below at which unequal ¯ows develop in the two branching ducts of the intake. With incompressible ¯ow analysis, they have shown that static pressure recovery characteristics at the junction of the two ducts govern the ¯ow instability. Further, they have also indicated that for equal ¯ow in the two ducts under steady state conditions, even a small disturbance grows to a larger magnitude at the junction. Sudhakar and Ananthkishnan [3] have presented a simple model to explain the phenomenon that causes transition from symmetric to asymmetric operation of these ducts in supersonic ¯ights. Investigations of other aspects on such intakes are not available in the open literature. Majorities of the studies are on single S- shaped diffusing ducts [4±14]. Over the last decade, computational ¯uid dynamics is being used extensively as a tool for analysing the ¯ow in complex geometries. This tool has also been used by many researchers to investigate diffusers [13±16]. The MS was received on 5 March 2003 and was accepted after revision for publication on 19 November 2003. * Corresponding author: Department of Applied Mechanics, Indian Institute of Technology Delhi, Hauz Khas, NewDelhi 11016, India. 23 G00703 # IMechE 2004 Proc. Instn Mech. Engrs Vol. 218 Part G: J. Aerospace Engineering