Navier-Stokes predictions for the F-18 wing and fuselage at large incidence

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Navier-Stokes solutions have been obtained using the Chimera overset grid scheme for flow over the wing, fuselage, and wing leading-edge extension (LEX) of the F-18 aircraft at high incidence. Solutions are also presented for flow over the fuselage forebody at high angles of attack. The solutions are for turbulent flows at high-Reynolds-number flight-test conditions, and are compared with available qualitative and quantitative experimental data. Comparisons of predicted surface flow patterns, off-surface flow visualizations, and surface- pressure distributions are in good agreement with flight-test data. The ability of the numerical method to predict the bursting of the LEX vortex as it encounters the adverse pressure gradient field of the wing is demonstrated. HIGH angle-of-attack technology program is currently underway Vvithin NASA. The objectives of the program include the development of flight-valida ted design methods that accurately predict the aerodynamics and flight dynamics of aircraft maneuvering in the high-angle-of-attack regime. Toward meeting these objectives, the program integrates ground-based experimental and computational investigations with flight-test investigations conducted on an F-18 at the NASA Ames-D den Flight Research Facility. The flight tests include surface 1 off-surface flow visualizations, as well as quantitative m irements of the flow surrounding the air- craft at large i ence. This database provides a unique op- portunity for C '•-).) code validation at actual high-alpha flight conditions. This paper presents results of Navier-Stokes com- putations of the flow about the wing, fuselage, and wing lead- ing-edge extension (LEX) of the F-18 at conditions matching those of the flight tests. Previous numerical predictions for the isolated F-18 fuselage forebody were reported in Refs. 1-3. Numerical prediction of the flow over aircraft flying at large angles of attack is a difficult aerodynamic problem. High- angle-of-attack flows contain large regions of three-dimen- sional separated flow, where the boundary layers leave the surface of the body along surfaces of separation, and roll up on the leeward side of the body to form strong, concentrated vortical flows. Separated flows historically have been treated by a wide variety of computational methods, ranging from simple potential flow methods to time-marching Navier-Stokes techniques. However, the close coupling that exists between the strength and location of the leeward vortical flow and the location of the viscous layer separation lines has precluded