ANALYSIS OF VORTEX BURSTING UTILIZING 3-DIMENSIONAL LASER MEASUREMENTS

From the analysis of experimental three-dimensional laser velocimeter data of a vortex burst condition on a generic fighter configuration, a criterion for vortex breakdown has been evaluated. The measured velocity vectors were rotated from the tunnel coordinate system to the vortex core trajectory to examine the relevant parameters for vortex instability. The Rossby parameters that govern stability were formulated in terms of the local vortex flow variables. The ratio of axial-to-crossflow energy evaluated from the data encompassing a region bounded by the vorticity provides for a parameter that is consistent with Ludwieg's spiral instability analysis for conical flow. Benjamin's analysis for supercritical flow transition is correlated with a parameter for the mean flow vortex variables. The magnitudes of the critical parameters decrease downstream from the adverse pressure gradient along the vortex trajectory providing a threshold that correlates with the vortex breakdown position.