Vortex Motions

The study of vortex motions is a classical subject of research which is still vigorously pursued and finds ever new applications of considerable intrinsic and practical interest. The formation of surfaces of discontinuity, or coherent vortex sheets, in the flow past bodies generally involves the consideration of the large‐scale flow field together with one or several core regions. The former includes the body and an outer part of the vortex sheet, which differ from case to case; the latter have certain common features in different cases. But distinctions can be made between three‐dimensional cores growing in space and two‐dimensional cores growing in time, and between single‐branched cores along the ends of main vortex sheets and double‐branched cores with the outer sheet extending to either side of the cores, possibly in a periodic array of subsidiary cores as in wakes. Vortex cores may alternatively be regarded as swirling flows with distributed vorticity; and inner viscous cores and outer inviscid cores can be distinguished. These core flows are smooth under certain conditions but in others such phenomena as vortex breakdown may occur. It is shown that the key features of the core flows are the same, whether the model used involves a spiral vortex sheet in irrotational flow or a swirling flow with distributed vorticity. The recent extensions of the knowledge of core flows could be used in future work to obtain improved solutions for complete flow fields. Some complete flows are described and the problems involved are briefly discussed, using the example of a lifting slender wing.