Starting vortex

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

Inclined Jet in Crossflow Interacting with a Vortex Generator

Abstract: An experiment is conducted on the effectiveness of a vortex generator in preventing liftoff of a jet in crossflow, with possible relevance to film-cooling applications. The jet issues into the boundary layer at an angle of 20 degreees to the freestream. The effect of a triangular ramp-shaped vortex generator is studied while varying its geometry and location. Detailed flowfield properties are obtained for a case in which the height of the vortex generator and the diameter of the orifice are comparable with the approach boundary-layer thickness. The vortex generator produces a streamwise vortex pair with a vorticity magnitude 3 times larger (and of opposite sense) than that found in the jet in crossflow alone. Such a vortex generator appears to be most effective in keeping the jet attached to the wall. The effect of parametric variation is studied mostly from surveys 10 diameters downstream from the orifice. Results over a range of jet-to-freestream momentum flux ratio (1 < J < 11) show that the vortex generator has a significant effect even at the highest J covered in the experiment. When the vortex generator height is halved, there is a liftoff of the jet. On the other hand, when the height is doubled, the jet core is dissipated due to larger turbulence intensity. Varying the location of the vortex generator, over a distance of three diameters from the orifice, is found to have little impact. Rounding off the edges of the vortex generator with the increasing radius of curvature progressively diminishes its effect. However, allowing for a small radius of curvature may be quite tolerable in practice.

Heat Transfer and Fluid Flow in a Square Duct With 12 Different Shaped Vortex Generators

Abstract: Detailed local Nusselt number distributions, streamwise mean flow patterns and cross-sectional secondary flow patterns, and friction factors in the first pass of a sharp turn two-pass square channel with various configurations of longitudinal vortex generator arranged on one wall were measured using transient liquid crystal thermography, laser-Doppler velocimetry, and pressure transducer probing, respectively. The Reynolds number, based on channel hydraulic diameter and bulk mean velocity, was fixed at 1.2 × 104. The vortex generator height-to-hydraulic diameter ratio and pitch-to-height ratio were 0.12 and 10, respectively. Comparisons in terms of heat transfer augmentation and uniformity and friction loss are first performed on 12 configurations of longitudinal vortex generator. The fluid dynamic mechanisms and wall confinement relevant to heat transfer enhancement are then documented for three-selected vortex generator models. In addition, the differences in fluid flow and heat transfer characteristics between a single vortex generator and a vortex generator array are addressed for the delta wing 1 U and 45° V U models which provide better thermal performance. The direction and strength of the secondary flow with respect to the heat transfer wall are found to be the most important fluid dynamic factors affecting the heat transfer promotion through the channel wall, followed by the convective mean velocity, and then the turbulent kinetic energy. Furthermore, the effects of the two-dimensional heat conduction near the vortex generator edge and unseen heat transfer areas on the Nusselt number estimation are documented in detail.Copyright © 1999 by ASME

Parameter dependence of vortex interactions on a two-dimensional plunging plate

Abstract: The structure and dynamics of the flow field created by a plunging flat-plate airfoil are investigated at a chord Reynolds number of 10,000 while varying plunge amplitude and Strouhal number. Digital particle image velocimetry measurements are used to characterize the shedding patterns and the interactions between the leading- and trailing-edge vortex structures (LEV and TEV), resulting in the development of a wake classification system based on the nature and timing of interactions between the leading- and trailing-edge vortices. The streamwise advancement of the LEV during a plunge cycle and its resulting interaction with the TEV is primarily dependent on reduced frequency; however, for Strouhal numbers above approximately 0.4, significant changes are observed in the formation of vortices shed from the leading and trailing edges, as well as the circulation of the leading-edge vortex. The functional form of the relationship between leading-edge vortex circulation and Strouhal number suggests that the Strouhal number dependence is more specifically a manifestation of the effective angle of attack. Comparison with low-Reynolds-number studies of plunging airfoil aerodynamics reveals a high degree of consistency and suggests applicability of the classification system beyond the range examined in the present work.

Vortex Motion Law for the Schrödinger--Ginzburg--Landau Equations

Abstract: In the Ginzburg--Landau model for superconductivity a large Ginzburg--Landau parameter $\kappa$ corresponds to the formation of tight, stable vortices. These vortices are located where an applied magnetic field pierces the superconducting bulk, and each vortex induces a quantized supercurrent about the vortex. The energy of large-$\kappa$ solutions blows up near each vortex, which brings about difficulties in analysis. Rigorous asymptotic static theory has previously established the existence of a finite number of the vortices, and these vortices are located precisely at the critical points of a renormalized energy. We consider the motion of such vortices in a dynamic model for superconductivity that couples a U(1) gauge-invariant Schrodinger-type Ginzburg--Landau equation to a Maxwell-type equation under the limit of large Ginzburg--Landau parameter $\kappa$. It is shown that under an almost-energy-minimizing condition each vortex moves in the direction of the net supercurrent located at the vortex posit...

A numerical study of dynamics of a temporally evolving swirling jet

Abstract: Direct numerical simulation (DNS) of a swirling jet near the outlet of a nozzle with axisymmetric and non-axisymmetric disturbances is performed to investigate the dynamic characteristics of the flow. The early (linear) stage of the jet evolution agrees well with the predictions of linear stability theory. In the nonlinear stage, the axisymmetric DNS shows that the interaction between the primary vortex ring and the streamwise columnar vortex creates a secondary vortex structure with opposite azimuthal vorticity near the columnar vortex. Then a vortex pair consisting of the primary and secondary vortices forms and travels radially away from the symmetry axis, causing a rapid increase of the thickness of mixing layer. The non-axisymmetric DNS shows that the streamwise vortex layer developed in the early stage of evolution due to azimuthal instability breakdowns into small eddies under the joint stretch of the axial and azimuthal shear. The results reveal several mechanisms of mixing enhancement by swirl, i.e., the radial motion of vortex ring pairs, the rapid growth of streamwise vorticity, and the creation of three-dimensional small eddies. They are all favorable for fluid entrainment in swirling jets.