This test case is concerned with the prediction of vortex breakdown above a delta wing with a sharp leading edge at high angle of attack. The lift force on a delta wing is mainly determined by the suction due to the vortices above the wing. These vortices are formed as the shear layers emanating from the leading edges roll up. As the angle of attack increases, the vortices become stronger and the lift increases, until the vortices break down, the suction effect is lost, and the lift drops strongly. Hence, the computation of vortex breakdown is relevant for the prediction of the performance of aircraft employing delta-type wings (e.g., fighter aircraft and UAV’s).
For this test case, the NASA delta wing geometry (Chu and Luckring, 1996) that was also used in the Second International Vortex Flow Experiment (VFE-2) is considered. It has a 65° leading-edge sweep and a sharp leading edge. The geometry includes a sting. The considered flow conditions are a Mach number of M = 0.07, a Reynolds number of Remac = 1·106 based on the mean aerodynamic chord cmac, and an angle of attack α = 23°. Experiments have been conducted by TU Munich (Furman and Breitsamter, 2008), including steady and unsteady surface pressure measurements as well as measurements of the mean and fluctuating velocity field at different chordwise stations.
Figure 1: Impression of experimental results.
Figure 2: Impression of computational results.
- Chu, J. and Luckring, J. M. (1996) Experimental surface pressure data obtained on 65° delta wing across Reynolds number and Mach number ranges, NASA TM 4645.
- Furman, A. and Breitsamter, Ch. (2008) Turbulent and unsteady flow characteristics of delta wing vortex systems, AIAA Paper 2008-0381.
- Second International Vortex Flow Experiment (VFE-2): http://www.dlr.de/as/VFE-2.