Axisymmetric Wave Motions and Instabilities in the Cores of Trailing Vortices

Cruising jet transport wake vortex flight data has been analysed for axisymmetic wave motions in the cores of the trailing vortices. Axisymmetric wave velocities have been compared with analytical, laboratory and numerical analyses, disclosing similarities and differences in wave velocities, magnitude and direction. Comparative emphases are placed upon the earlier work of Maxworthy et al and Moet et al, which included vortex breakdown as an outcome of wave transmissions in the cores, leading to transformations to higher orders, of azimuthal vorticity, associative substantially larger core radius, and subsequent reformations. Both have similarities to jet transport cruising flight wake vortex data, as measured by the NRC. Furthermore, the non-dimensional fundamental axisymmetric wave speeds are very similar between NRC flight data and the earlier research. They showed a mild dependency upon the amplitude of wave disturbances, as effected by the ratio in the core radius change initiating the wave. Flight data included two higher order wave speed characteristics. A case analysis of higher orders of azimuthal vorticity has been conducted; namely, in response to travelling pressure waves, a unipolar wake vortex core is perturbed, vented, and discretised into an N (k) ring vortex, each of same-sign strength Γ/N, followed by reformation. The case consisted of a sample of vortex core traverses, during a jet transport wake vortex survey. For the traverse sample, the modal states was evenly divided between N=1 and N=[5-7], with lesser modes at N=2, 4.