Starting vortex

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

Turbulence inside a vortex

Abstract: Following Bradshaw’s analogy between rotating and stratified flows, the turbulence within a vortex is analyzed using a new model for stratified entrainment. At the vortex radius where the tangential velocity is a maximum, the model predicts that the flow is so strongly “stratified” that even the smallest turbulent eddies are incapable of transporting fluid there. The growth of the vortex is thus limited by molecular viscosity, even though the vortex Reynolds number is large. The model prediction is compared to experiments in the literature of wingtip vortices. The result is consistent with the remarkable observations of laminar-like growth of this turbulent flow.

Vortex interaction of tandem pitching and plunging plates: a two-dimensional model of hovering dragonfly-like flight

Abstract: The force evolution and associated vortex dynamics on a nominal two-dimensional tandem pitching and plunging configuration inspired by hovering dragonfly-like flight have been investigated experimentally using time-resolved particle image velocimetry. The aerodynamic forces acting on the flat plates have been determined using a classic control-volume approach, i.e. a momentum balance. It was found that only the tandem phasing of ψ = 90° was capable of generating similar levels of thrust when compared to the single-plate reference case. For this tandem configuration, however, a much more constant thrust generation was developed over the cycle. Further examination showed that the force and vortex development on the fore-plate was unaffected by the tandem configuration and that nearly all variations in performance could be attributed to the vortex interaction on the hind-plate. By calculating the trajectory and strength of the hind-plate's trailing-edge vortex, the chain-like vortex interaction mechanism responsible for improved performance at ψ = 90° could be identified. The underlying result from this study suggests that the dominant vortex interaction in dragonfly flight is two dimensional and that the spanwise flow generated by root-flapping kinematics is not entirely necessary for efficient propulsion but potentially due to evolutionary restrictions in nature.

Growth and separation of a start-up vortex from a two-dimensional shear layer

Abstract: The evolution of an isolated line vortex generated by a starting two-dimensional jet is studied experimentally using time-resolved particle image velocimetry. The vortex growth in this current configuration is not linked to any externally imposed length scales or interactions with other vortical structures or walls that could potentially influence vortex growth. A model for the early-stage vortex growth, based on the transport of circulation from the shear layer into the vortex, is proposed and found to agree well with experimental data. The model provides a scaling scheme for vortex growth using shear-layer characteristic velocity and shear-layer thickness. The vortex growth is limited through a gradual separation of the vortex from the feeding shear layer, arising from decreased shear-layer curvature. This phenomenon is linked to a competition between the shear-layer tendency to remain in the streamwise direction and the induced velocity from the vortex on the shear layer. Finally, a dimensionless number representing this competition is introduced, which in turn is able to describe the gradual separation of the vortex from the shear layer.

A new vortex method of plasma insulation and explanation of the Ranque effect

Abstract: The efficiency of thermal insulation of a microwave-generated plasma using reverse vortex flow was investigated experimentally and by numerical simulations. Comparison with the conventional vortex method of plasma insulation was made. Changing the location of the vortex inlet to the exit end of the plasma torch leads to a significant decrease of the heat loss to the wall; from 30% to 5%. This result contradicts the traditional explanation of the Ranque effect. A new simple explanation of the Ranque effect of energy separation in the vortex tube is proposed. Energy separation takes place due to radial motion of turbulent micro-volumes with differing tangential velocities in the strong centrifugal field. The new model of energy separation explains such apparently mysterious phenomena as the counter-rotation of the central vortex flow layers observed in some experiments and in numerical simulations. A new approach for consideration of the confined vortex flows is described.