Wind tunnel experiments and Navier-Stokes computations of a high-lift military airfoil

Abstract

Abstract : This paper describes results of wind tunnel experiments and Navier-Stokes computations conducted to help understand high-lift aerodynamics about thin, fighter type, multi-element airfoils at flight Reynolds numbers and lift coefficients up to climax. The wind tunnel tests were conducted in the NASA Langley Research Center (LARC) Low Turbulence Pressure Tunnel (LTPT) as part of a cooperative effort between the Navy, Boeing, and NASA LARC. Surface pressures, forces and moments, transition data using hot films were measured on a two dimensional (2-D) airfoil model of a Boeing advanced fighter wing section configured with a deflected leading edge flap, shroud and a slotted trailing edge flap. Effects of Reynolds number, trailing edge flap gap and overhang, Gurney flap, vortex generators on c(lmax) were investigated. Navier-Stokes computations were performed using structured/chimera grid for several of these configurations. The computations were done with the Baldwin-Barth, Spalart-Allmaras one equation turbulence models and the Shear stress transport two-equation turbulence model to predict the Reynolds number effects. The lift coefficient was predicted within 3% of the experiment up to and including stall angles-of-attack. Trends in maximum lift as a function of Reynolds number and Mach number are accurately predicted indicating that the CFD method could be used to extrapolate sub-scale high-lift system aerodynamic performance to flight scale at angles of attack up to and including maximum lift. The trends of the effects of flow control mechanisms such as Gurney flaps were correctly predicted. Results from fully turbulent Navier-Stokes calculations are also correlated with the boundary layer transition data obtained from hot film measurements.