A NUMERICAL INVESTIGATION OF AEROFOIL BOUNDARY-LAYER MANIPULATOR PROFILE FOR CRUISE-FLIGHT CONDITIONS

A computational study has been conducted to determine the variation of device drag with profile shape and angle of attack for aerofoil bound ary-layer manipulators (LEBUs) operating at high subsonic Mach numbers . Calculations have been made at a free-stream Mach number of 0.80 for both symmetrical and asymmetrical NACA-00xx and 44xx series devices i ncluding an inverted cambered NACA-4409 profile. The LEBUs considered were located in a turbulent boundary-layer at a mid-chord height h equ ivalent to 0.67 delta from the wall. The present investigations sought to confirm suggestions based upon experimental observations that ther e may be some advantage in replacing a symmetrical device by an invert ed asymmetrical profile form. The computations were performed using an unstructured adaptive-mesh 3D Navier-Stokes code incorporating a Lam and Bremhorst low-Reynolds number two-equation k - epsilon turbulence model. The calculated flow field around a NACA-0009 aerofoil at zero a ngle of attack was initially verified against experimental interferome tric data. The calculated device drag coefficient at zero incidence wa s 0.026 for the NACA-0009, similar to that measured in experiments. Ho wever predicted drag for an inverted NACA-4409 was 0.085, this being c onsiderably higher than anticipated. The results suggested that a slig htly positive angle of attack may help minimise device drag but neithe r profile is appropriate for use in transonic conditions. Improved res ults may be obtained from inverted flat-topped profiles designed to mi nimise losses associated with localised shocks.