Topic
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 article, the authors investigated the off-surface aerodynamic characteristics of a wing in ground effect using a number of methods including laser Doppler anemometry and particle image velocimetry.
Abstract: The off-surface aerodynamic characteristics of a wing in ground effect are investigated using a number of methods including laser Doppler anemometry and particle image velocimetry. The study focuses on two aspects of the flow: turbulent wake and edge vortex. These features are closely associated with the behavior of the aerodynamic force in ground effect. The size of the wake increases in proximity to the ground. A downward shift of the path of the wake is also observed. Discrete vortex shedding is seen to occur behind the wing. As the wing height is reduced, separation occurred on the suction surface of the wing, and the spanwise vortex shedding is found to couple with a flapping motion of the wake in the transverse direction. An edge vortex is also observed off the edge of the end plate of the wing, which contributes to force enhancement and helps to define the force behavior in the force enhancement region. The rate of change in the downforce vs height curve is linked to the strength of the edge vortex. The vortex breakdown signals a slowdown in the force enhancement. When the maximum downforce height is reached, the edge vortex breaks down completely.
59 citations
TL;DR: In this paper, the authors uncover a mechanism involving the creation of a vortex ring which plays a central role in escaping segmentation, which is fundamental to the understanding of how liquid volumes relax.
Abstract: A liquid filament recoils because of its surface tension. It may recoil to one sphere, the geometrical shape with lowest surface, or otherwise segment to several pieces which individually will recoil to spheres. This experiment is classical and its exploration is fundamental to the understanding of how liquid volumes relax. In this paper, we uncover a mechanism involving the creation of a vortex ring which plays a central role in escaping segmentation. The retracting blob is connected to the untouched filament by a neck. The radius of the neck decreases in time such that we may expect pinch-off. There is a flow through the neck because of the retraction. This flow may detach into a jet downstream of the neck when fluid viscosity exceeds a threshold. This sudden detachment creates a vortex ring which strongly modifies the flow pressure: fluid is expelled back into the neck which in turn reopens.
59 citations
TL;DR: In this paper, an experiment was performed to quantify the interdependence of viscous/turbulent diffusion and straining effects on the development of helicopter rotor tip vortices, and it was shown that vortex stretching begins to decrease the viscous core size, and when the strain rates become large, this can balance the normal growth in the vortex core resulting from diffusion.
Abstract: An experiment was performed to help quantify the interdependence of viscous/turbulent diffusion and straining effects on the development of helicopter rotor tip vortices. The properties of the blade tip vortices were measured in the wake of a small-scale hovering rotor and compared to the results for the case when the wake approached a solid boundary. The presence of the boundary created velocity gradients that forced the tip vortex filaments to strain, allowing the effects of this process on the vortices to be measured relative to the baseline case without the boundary. It is shown that vortex stretching begins to decrease the viscous core size, and when the strain rates become large, this can balance the normal growth in the vortex core resulting from diffusion. The present results were used to help develop a more general tip vortex model suitable for use in a variety of helicopter rotor aeroacoustic applications. The proposed engineering model combines the effects of turbulent diffusion and strain on the vortex core growth. The empirical coefficients of this model have been derived based on the best available results from rotating-wing tip vortex measurements.
58 citations
TL;DR: In this paper, the authors investigate the transition between the helical mode instability and the vortex shedding and find that this transition is abrupt, as indicated by a jump in the frequency parameter, and that it occurs at the angle of attack at which breakdown reached the apex.
Abstract: Experimental evidence suggests that vortex breakdown is not the only source of buffeting of delta wings and fins. Other unsteady flow phenomena that contribute to buffeting at high angles of attack are fluctuations of vortex breakdown location and vortex shedding. Flow visualization and velocity measurements were carried out over a delta wing, over a wide range of angles of attack, to understand the transition between the helical mode instability and the vortex shedding. It was found that this transition is abrupt, as indicated by a jump in the frequency parameter, and that it occurs at the angle of attack at which breakdown reached the apex. The unsteady nature of vortex breakdown location was investigated by flow visualization for the interaction of vortex breakdown with a rigid flat plate. Although there are indications of a feedback effect on vortex breakdown, the amplitude of the fluctuations of breakdown location is smaller for impinging flows
58 citations
TL;DR: In this article, two discrete vortex models of oscillating flow above two-dimensional vortex ripples are presented, a simple inviscid model, which contains no diffusion of vorticity, and a cloud-in-cell (CIC) model with diffusion represented by random walk.
58 citations