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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 effects on mean flow and turbulence caused by meander of a vortex embedded in a two-dimensional boundary layer were investigated experimentally by driving a forced lateral oscillation of the vortex generator.
Abstract: The effects on mean flow and turbulence caused by meander of a vortex embedded in a two-dimensional boundary layer were investigated experimentally by driving a forced lateral oscillation of the vortex generator. Upstream, the vorticity contours without forcing were found to be round. The forced vortex generator oscillation caused a flattening of the time-averaged vorticity contours and changes in some of the Reynolds stresses. The results indicate that the unforced vortex did not meander significantly upstream, and that the effects of meander can be understood qualitatively from production of Reynolds stresses by the forced motion acting with the exiting three-dimensional velocity field. Farther downstream, the observed differences in the mean vorticity and Reynolds stresses caused by forcing were smaller, mainly because the vortex was substantially diffused at this station, resulting in smaller mean velocity gradients.

41 citations

Journal ArticleDOI
TL;DR: In this article, the instantaneous and time-averaged flow fields in the tip region of a ducted marine propulsor are examined, where a primary tip-leakage vortex interacts with a secondary, co-rotating trailing edge vortex and other co-and counterrotating vorticity found in the blade wake.
Abstract: The instantaneous and time-averaged flow fields in the tip region of a ducted marine propulsor are examined. In this flow, a primary tip-leakage vortex interacts with a secondary, co-rotating trailing edge vortex and other co- and counter-rotating vorticity found in the blade wake. Planar particle imaging velocimetry (PIV) is used to examine the flow in a plane approximately perpendicular to the mean axis of the primary vortex. An identification procedure is used to characterize multiple regions of compact vorticity in the flow fields as series of Gaussian vortices. Significant differences are found between the vortex properties from the time-averaged flow fields and the average vortex properties identified in the instantaneous flow fields. Variability in the vortical flow field results from spatial wandering of the vortices, correlated fluctuations of the vortex strength and core size, and both correlated and uncorrelated fluctuations in the relative positions of the vortices. This variability leads to pseudo-turbulent velocity fluctuations. Corrections for some of this variability are performed on the instantaneous flow fields. The resulting processed flow fields reveal a significant increase in flow variability in a region relatively far downstream of the blade trailing edge, a phenomenon that is masked through the process of simple averaging. This increased flow variability is also accompanied by the inception of discrete vortex cavitation bubbles, which is an unexpected result, since the mean flow pressures in the region of inception are much higher than the vapor pressure of the liquid. This suggests that unresolved fine-scale vortex interactions and stretching may be occurring in the region of increased flow variability.

41 citations

Journal ArticleDOI
TL;DR: In this article, a vortex model of inviscid propeller and wind-turbine wakes is proposed based on an asymptotic expansion of the Biot-Savart induction law to account for the finite vortex core size.
Abstract: A new vortex model of inviscid propeller and wind-turbine wakes is proposed based on an asymptotic expansion of the Biot-Savart induction law to account for the finite vortex core size. The circulation along the blade is assumed to be constant from the blade root to the tip approximating a turbine with maximum power production for given operating conditions. The model iteratively calculates the tip-vortex path, allowing the wake to expand/contract freely, and is afterward able to evaluate the velocity field in the whole domain. The 'roller-bearing analogy', proposed by Okulov and Sorensen (J. Fluid Mech., vol. 649, 2010, pp. 497-508), is used to determine the vortex core size. A comparison of the main outcomes of the present model with the general momentum theory is performed in terms of the operating parameters (namely the number of blades, the tip-speed ratio, the blade circulation and the vortex core size), demonstrating good agreement between the two. Furthermore, experimental data have been compared with the model outputs to validate the model under real operating conditions.

40 citations

Journal ArticleDOI
TL;DR: In this article, three-component particle image velocimetry (PIV) measurements of blade tip vortices of a full-scale helicopter in simulated hover flight in ground effect were conducted.
Abstract: Blade tip vortices are the dominant vortical structures of the helicopter flow field. The inherent complexity of the vortex dynamics has led to an increasing interest in full-scale in situ experiments, where the near field, closely behind the blade, is of particular interest, since measures of vortex control mostly target this initial stage of development. To examine the near field, three-component particle image velocimetry (PIV) measurements of blade tip vortices of a full-scale helicopter in simulated hover flight in ground effect were conducted. A feasible and robust evaluation procedure was developed to minimise the shortcomings of full-scale PIV applications, such as a moderate spatial resolution and an elevated measurement noise level. At vortex ages ranging from $$\psi_{\rm v}=1^{\circ}$$ to 30°, a pronounced aperiodicity and asymmetry of the vortex were observed in -sections perpendicular to the vortex axes. At $$\psi_{\rm v}=1^{\circ}$$ , a preferential orientation of the vortex was observed. For increasing wake age, vortex wandering increased while the asymmetry of the vortex cores decreased. The high level of aperiodicity and core asymmetry must be taken into account when considering phase-averaged vortex characteristics in the near wake region.

40 citations

Journal ArticleDOI
TL;DR: In this article, the authors used computational fluid dynamics to examine the behavior of delta wings placed in a transonic freestream and showed that a shock/vortex interaction is responsible for the sudden movement of the vortex breakdown location.
Abstract: It has been observed that delta wings placed in a transonic freestream can experience a sudden movement of the vortex breakdown location as the angle of incidence is increased. The current paper uses computational fluid dynamics to examine this behavior in detail. The study shows that a shock/vortex interaction is responsible. The balance of the vortex strength and axial flow and the shock strength are examined to provide an explanation of the sensitivity of the breakdown location. Limited experimental data are available to supplement the computational fluid dynamics results in certain key respects, and the ideal synergy between computational fluid dynamics and experiments for this problem is considered.

40 citations


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