Application of turbulence models to separated high-angle-of-attack flows

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Aircraft with slender bodies and swept lifting surfaces, flying at high angles of attack, often have regions of three-dimensi onal separated flow characterized by strong off-body vortices. One approach to numerically simulate this class of high Reynolds number flows is to use the Reynolds-averaged Navier-Stokes equations (RANS), together with a turbulence model. Many turbulence models have been utilized for the RANS equations, however most are developed and calibrated for configurations with attached boundary layers or flows with shockinduced separation. In order to apply these models to separated flows with strong off-body vortices, modifications are usually necessary. This investigation examines the development and application of these modifications for both the algebraic Baldwin-Lomax turbulence model, and the one-equation Spalart-Allmaxas model. The implementation of these modified models differs among several production computational fluid dynamics (CFD) codes, as do their computed results. Model behavior in predicting crossflow separation for an ogive cylinder, and leadingedge separation for a delta wing are examined. The flowfields for the ogive cylinder and delta wing geometries are simulated at 20° and 15° angle of attack respectively. Both configurations are computed at subsonic flow speeds, however applications to transonic and supersonic wingbody configurations are discussed. Comparisons are made with experimental surface pressure measurements, and surface oil-flow visualizations where available.