Starting vortex

About: Starting vortex is a research topic. Over the lifetime, 4785 publications have been published within this topic receiving 100419 citations.

The formation and maintenance of a leading-edge vortex during the forward motion of an animal wing

Abstract: A simple model is presented to explain the observed generation of a quasi-steady vortex at the leading edge of an animal wing that rotates in a horizontal plane about a body-centred axis. Vorticity formed by separation at the leading edge is transported outwards by a spanwise velocity field generated by two sources of spanwise pressure gradient, one induced centrifugally and the other by variations in the vortex size and circulation. The vorticity is then deposited into a trailing vortex system that takes the form of a downward propagating vortex ring. This mechanism appears to apply generally to flying animals but is modelled here for those in hovering flight.

Vortex structure in the wake of a sphere

Abstract: Results showing the three‐dimensional vortex shedding structure when a sphere is towed at a constant velocity through a stratified fluid are presented. It is found that for small Richardson numbers (weak stratification) and Reynolds numbers in the range from 4×103 to 2×104 the vortex is shed three‐dimensionally. However, stratification quickly and effectively inhibits the vertical motion and the initially turbulent wake collapses and reveals the vertically oriented portion of the vortex structure, reminiscent of a two‐dimensional vortex street behind a circular cylinder when viewed from above. The structure is, however, distinctly three‐dimensional. It is also found that the estimated vortex shedding frequency is in reasonable agreement with previously published results for a sphere in a homogeneous fluid. It is suggested that a weak stratification is an excellent means for revealing the vortex structure of a three‐dimensional body in a homogeneous fluid, and that the vortex tube in the wake of a sphere in a homogeneous fluid has a closed‐end double helical structure. Two branches of the double helix are continuously unwinding in an opposite sense from the formation region. Moreover, the present double helical model satisfies Thompson’s circulation theorem in contrast to previously proposed helical models.

Experimental Study of the Formation of a Vortex Ring at the Open End of a Cylindrical Shock Tube

Abstract: Schilieren spark snapshots spaced at electronically controlled intervals of several hundredths of a millisecond show the emergence of the shock wave and the formation of the vortex ring at the end of a cylindrical shock tube, open to the atmosphere. The axial positions of the vortex ring and shock front are plotted as a function of time for the first millisecond, in which time the vortex forms and is accelerated to about three‐quarters of the theoretical particle velocity of the mass flow following the initial plane shock. The diameter of the vortex ring increases nonlinearly with time and distance.

Study of Mechanism of Ring-Like Vortex Formation in Late Flow Transition

Abstract: In this paper a new study for the mechanism of the single and multiple ring-like vortex formation is presented. There were two existing theories, one believes the ring-like vortex is produced by the shear layer and the other thinks the ring-like vortex generation follows the Crow theory. According to our recent DNS results, a new hypothesis is presented that the ring-like vortices generation is caused by the interaction between the �-shaped vortex tube and streamwise vortices. The formation of ring head and ring neck are the results of the interaction between the prime streamwise vortices and secondary streamwise vortices. The multiple ringlike vortex generation is following the first Helmholtz vortex conservation law. A number of new unknown phenomena are revealed, mechanisms are presented and new theories are established by this new DNS study Nomenclature