ON THE STRUCTURE OF VORTEX BREAKDOWN ON A DELTA-WING

This paper presents a detailed description of the vortex breakdown phe nomenon on a delta wing. While there have been a number of earlier stu dies which have given us a broad, overall picture of these interesting and important flow fields, none has so far yielded the kind of fine s tructure considered here, in spite of using very fine grids. The prese nt work has been made possible by the use of a new type of grid, calle d the embedded conical grid, which exploits the special nature of the flow field. Based on the Euler equations, the flow field past a 70 deg rees sharp-edged delta wing in a subsonic free-stream is resolved here using this grid. The breakdown is found to begin as a rapid decelerat ion of the inner core due to a sudden increase in the adverse axial pr essure gradient. This leads to a sudden broadening of the core and the formation of a deficit velocity region which becomes intensified caus ing axial flow reversal. The near-axis vorticity lines get tilted away from the vortex axis and their spiralling direction is reversed. The effect of artificial dissipation and grid coarseness on the computed v ortex breakdown has been examined. The results presented here, though obtained for the delta tying geometry, are expected to add to our unde rstanding of vortex breakdown in other flow situations as well.