22nd Congress of International Council of the Aeronautical Sciences, Harrogate, UK, 28 August - 1st September, 2000
Paper ICAS 2000-5.2.1

CIVIL AIRCRAFT ENGINE INTAKES WITH NEGATIVE SCARF INSPIRED BY REQUIREMENTS FOR ACOUSTIC REDUCTIONS - PRELIMINARY, AERODYNAMIC PERFORMANCE ASSESSMENT

R. K. Nangia, M. E. Palmer
Nangia Aero Research Associates, Bristol, UK

Keywords: aircraft engine intake, negative scarf, acoustic reduction

Aircraft engines must meet current and future FAR regulations and noise "footprints" criteria. A way of reducing noise is to use negatively scarfed inlets. The extended lower lip acts as an acoustic "barrier". We need to understand the aerodynamic implications of inlet scarfing at low and transonic speeds. The subsonic aerodynamic performance (incidence, side-slip and ground effects) of a conventional (+6° scarf) inlet has been assessed. A range of negative scarf angles was applied to the geometry and the subsonic performance of the resulting inlets assessed. A staged, iterative design process was carried out on a -20° scarfed inlet from this series. This led to modified lip geometry that gave attached flow capability equivalent to the datum "conventional" inlet. An additional advantage for negative scarf was the weakening of the ground vortex at "zero forward speed". This is important for "large" intakes with high by-pass ratios, set closer to the ground. The transonic performance of the conventional (+6° scarf) and negatively scarfed inlet (-20°) was assessed. A limited design study was carried out on the -20° inlet to understand the effects of lip shaping at high speed (Mach 0.8). An encouraging equivalence has been achieved between the datum and scarfed inlet and further detailed work (internal surfaces) leading to experiments has been recommended. Work is needed on scarf angle choice.

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