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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: In this paper, the generation and development of vortex rings are simulated by numerical integration of the Navier-Stokes equation as an initial and boundary value problem, and time variations of physical quantities such as total energy, impulse and velocity of the vortex rings, etc. are obtained, and compared with those obtained from the asymptotic expansion.
Abstract: Decay of a vortex ring in a viscous fluid is discussed by using a solution in the form of an asymptotic expansion for large time t . It is found that the velocity of the vortex ring varies as t -1.5 in the final state of low Reynolds number. The asymptotic expansion is not uniformly valid, and an improvement is made by using the method of matched asymptotic expansions. Generation and development of vortex rings are simulated by numerical integration of the Navier-Stokes equation as an initial and boundary value problem. Time variations of physical quantities such as total energy, impulse and velocity of the vortex rings, etc. are obtained, and have been shown to approach asymptotically to those obtained from the asymptotic expansion. Comparison with experimentally produced vortex rings is also given briefly.

37 citations

Journal ArticleDOI
TL;DR: In this paper, a merging distance criterion for equal strength corotational vortices is derived from low-turbulence wind tunnel flow visualization data, and the vortex separation distance is normalized by defining a vortex core diameter based on circulation defect and angular momentum defect.
Abstract: A merging distance criterion for equal-strength corotational vortices is derived from low-turbulence wind tunnel flow visualization data. The vortex separation distance is normalized by defining a vortex core diameter based on circulation defect and angular momentum defect. Merging may take place for larger separation distances than predicted from earlier two-dimensional inviscid calculations, which indicates that viscosity and possibly three-dimensional effects are important factors in the merging phenomenon. Hot-wire velocity distributions and rolling moment measurements show that attenuation of the vortex hazard is associated with vortex merging. Nomenclature bg = generator wingspan bf = follower wingspan CL = lift coefficient cf = rolling-moment coefficient c = wing chord d = vortex separation distance d0 = initial vortex separation distance dc = vortex core diameter (usually based on peak tangential speed) dM = vortex core diameter (based on angular momentum defect equal to that in a Rankine vortex) dr = vortex core diameter (based on circulation defect equal to that in a Rankine vortex) dv —vortex core diameter (based on outer boundary of.the rotational portion of the vortex)

37 citations

Journal ArticleDOI
TL;DR: In this article, the effect of vortex generators on the flow near stall was investigated in a purpose-built wind tunnel for airfoil investigations on a DU 91-W2-250 profile.
Abstract: Stereoscopic Particle Image Velocimetry measurements investigating the effect of vortex generators (VGs) on the flow near stall were carried out in a purpose-built wind tunnel for airfoil investigations on a DU 91-W2-250 profile. Measurements were conducted at Re = 0.9⋅106, corresponding to free stream velocity U∞ = 15 m s−1. The objective was to investigate the flow structures induced by the vortex generators and study their separation controlling behavior on the airfoil. The uncontrolled flow (no VGs) displayed unsteady behavior with separation as observed from large streamwise velocity variations. The corresponding controlled flow (with VGs) showed the same unsteadiness, where the appearance of the vortex structures alternated with a much less separated or even attached boundary layer as also seen in the measured airfoil data: CL = 1.56, CD = 0.116 with VGs and CL = 1.16, CD = 0.135 without. On average, the controlled flow left an attached flow as opposed to the uncontrolled one. Mixing close to the wall, transferring high momentum fluid into the near wall region, was observed, and the hypothesis of variations in the streamwise velocity component in the boundary layer was supported by a Snapshot Proper Orthogonal Decomposition analysis. This analysis also revealed some of the dynamics of the induced vortices. Copyright © 2012 John Wiley & Sons, Ltd.

37 citations

Patent
09 Jul 2010
TL;DR: In this paper, a plan-form edge vortex generator is used to improve the aerodynamic performance of foils by mixing free stream flow into the boundary layer while minimising separation and fluid losses.
Abstract: A method of improving aerodynamic performance of foils by the application of conformal, low drag vortex generators. A film of erosion protection material or other conformal material is placed on the foil to provide a medium for the incorporation of planform edge vortex generators. The form edge is shaped to achieve submerged vortex generating shapes of chevron or ogival planforms, extending primarily chordwise on the foil surface. The vortex generators promote improved boundary layer dynamics by mixing free stream flow into the boundary layer while minimising separation and fluid losses. At the trailing edge, the shape formed with the chevrons applied apex forward, acts as a vented gurney tab series and additionally as disruptors to the Von Karman Street wake, delaying sheet rollup into the tip vortice.

37 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202336
202278
20217
20207
20196
201815