22nd Congress of International Council of the Aeronautical Sciences, Harrogate, UK, 28 August - 1st September, 2000
Paper ICAS 2000-2.5.2

NUMERICAL ANALYSIS OF THE UNSTEADY FLOW ABOVE A SLENDER DELTA WING AT LARGE ANGLES OF ATTACK

J. Müller , D. Hummel
Institute of Fluid Mechanics, Technical University Braunschweig, Germany

Keywords: numerical analysis, delta wing, large angle of attack

The unsteady, bursted vortical flow above the fixed VFE delta wing at large angles of attack was analyzed by time-accurate Euler and Navier-Stokes calculations. For an inviscid Euler code the situation within the primary vortex core is dominated by numerical dissipation. The same is true for a Navier-Stokes code using the algebraic Baldwin-Lomax turbulence model, which only provides additional turbulent eddy viscosity within the boundary layer near the wall. Therefore, both methods have to be calibrated e.g. by an experimentally proved breakdown position. On the other hand, the two-equations k-? turbulence model of Wilcox is able to provide sufficient turbulent eddy viscosity within the primary vortex core. Such a method becomes independent from the artificial numerical dissipation k(4) and the grid resolution. The time-accurate Euler calculations were calibrated at a = 18. Such an adapted Euler code is able to predict the breakdown positions and the frequencies of the breakdown process correctly for almost the whole angle of attack range. The influence of the secondary vortex on the breakdown process of the primary vortex is limited to small angles of attack and leads for a calibrated Euler calculation to a further downstream located breakdown position and to higher dominating frequencies compared to Navier-Stokes results. For higher angles of attack the differences diminish. Finally, the deadwater-type flow at very high angles of attack is predicted identically by both numerical methods.

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