22nd Congress of International Council of the Aeronautical Sciences, Harrogate, UK, 28 August - 1st September, 2000
Paper ICAS 2000-2.8.2

STUDY OF METHODS AND PHILOSOPHIES FOR DESIGNING HYBRID LAMINAR FLOW WINGS

P. W. C. Wong, M. Maina
Aircraft Research Association Ltd, Bedford, UK

Keywords: hybrid, laminar, wing flow, design

An investigation into methods of controlling attachment line, crossflow and Tollmien- Schlichting instabilities in order to delay transition and the implications for designing hybrid laminar flow (HLFC) wings for civil transport aircraft has been carried out. The control of these instability modes has been investigated in the form of a parametric study for a range of pressure distributions and flow conditions. A control technique commonly used is surface suction in the leading edge region. Results show that with this technique, the structural constraint of requiring the porous surface to be forward of the wing front spar would limit the extent of laminar flow that can be obtained. This constraint may be overcome by the use of surface cooling instead of suction downstream of the front spar for suppressing TS instability in order to achieve a greater extent of laminar flow. For HLFC wing design, it is important to consider the drag rise characteristics and lift capability in addition to viscous drag reduction. Analysis of the aerodynamic performance characteristics of aerofoils with different types of pressure distribution suggests that the same type of upper surface pressure distribution with an adverse ‘rooftop’ gradient may be chosen for an HLFC wing as for a turbulent wing. This type of pressure distribution may be suitable for the inner wing leading to performance benefits in terms of lift increment and skin friction drag reduction.

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