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Starting vortex
About: Starting vortex is a research topic. Over the lifetime, 4785 publications have been published within this topic receiving 100419 citations.
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TL;DR: With a Biot-Savart model of vortex filaments to provide initial conditions, a finite difference scheme for the incompressible Navier-Stokes equation is used in the region of closest approach of two vortex rings and it is seen that the low pressure which develops between the interacting vorticity regions causes the distortion of the initially circular vortex cross section.
Abstract: With a Biot-Savart model of vortex filaments to provide initial conditions, a finite difference scheme for the incompressible Navier-Stokes equation is used in the region of closest approach of two vortex rings. In the Navier-Stokes solution, we see that the low pressure which develops between the interacting vorticity regions causes the distortion of the initially circular vortex cross section and forces the rearrangement of vorticity on a convective time scale which is much faster than that estimated from viscous transport.
123 citations
TL;DR: In this paper, the formation and growth of a hairpin vortex in a flat-plate boundary layer and its later development into a young turbulent spot were studied. But they did not consider the formation of hairpin heads.
Abstract: Direct numerical simulation was used to study the formation and growth of a hairpin vortex in a flat-plate boundary layer and its later development into a young turbulent spot. Fluid injection through a slit in the wall triggered the initial vortex. The legs of the vortex were stretched into a hairpin shape as it traveled downstream. Multiple hairpin vortex heads developed between the stretched legs. New vortices formed beneath the streamwise-elongated vortex legs. The continued development of additional vortices resulted in the formation of a traveling region of highly disturbed flow with an arrowhead shape similar to that of a turbulent spot.
123 citations
TL;DR: In this paper, an in-depth characterization of the vortex formation and breakup process in a forced laminar separation bubble is presented, exploiting the largely periodic character of the flow in time as well as in the spanwise direction.
Abstract: The convective primary amplification of a forced two-dimensional perturbation initiates the formation of essentially two-dimensional large-scale vortices in a laminar separation bubble. These vortices are then shed from the bubble with the forcing frequency. Immediately downstream of their formation, the vortices get distorted in the spanwise direction and quickly disintegrate into small-scale turbulence. The laminar-turbulent transition in a forced laminar separation bubble is dominated by this vortex formation and breakup process. Using numerical and experimental data, we give an in-depth characterization of this process in physical space as well as in Fourier space, exploiting the largely periodic character of the flow in time as well as in the spanwise direction. We present evidence that a combination of more than one secondary instability mechanism is active during this process. The first instability mechanism is the elliptic instability of vortex cores, leading to a spanwise deformation of the cores with a spanwise wavelength of the order of the size of the vortex. Another mechanism, potentially an instability of flow in between two consecutive vortices, is responsible for three-dimensionality in the braid region. The corresponding disturbances possess a much smaller spanwise wavelength as compared to those amplified through elliptic instability. The secondary instability mechanisms occur for both fundamental and subharmonic frequency, respectively, even in the absence of continuous forcing, indicative of temporal amplification in the region of vortex formation. © 2013 Cambridge University Press.
123 citations
TL;DR: In this article, the various types of vortex generation and the related response characteristics of bluff bodies are described, and the symmetrical vortex shedding, which is enhanced by the longitudinally fluctuating flow for 2-D rectangular cylinders with a 0.5 side ratio, and one-shear layer related vortices, which are generated on the side surfaces of flat 2-dimensional rectangular cylinders and many bridge girder box sections by the stimulation of body motion or applied sound, are introduced.
122 citations
TL;DR: In this article, an industrial cambered controlled-diffusion airfoil is placed at the exit of an open-jet anechoic wind tunnel, with a jet width of about four chord lengths.
Abstract: A previous experimental investigation of the broadband self noise radiated by an industrial cambered controlled-diffusion airfoil embedded in an homogeneous flow at low Mach number has been extended to various aerodynamic loadings. The instrumented airfoil is placed at the exit of an open-jet anechoic wind tunnel, with a jet width of about four chord lengths. Sound is measured in the far field at the same time as the statistical properties of the wall-pressure fluctuations close to the trailing edge. A new set of mean wall-pressure data has been collected on this airfoil at a chord Reynolds number of 2.9 x 105, which provides some insight on the Reynolds-number effect. Two previously investigated flow regimes with different statistical behaviors are investigated by changing the angle of attack from 8 to 15 deg. They respectively correspond to the nearly separated boundary layer with vortex shedding at the trailing edge and to the turbulent boundary layer initiated by a leading-edge separation.
122 citations