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Three-dimensional numerical simulation of the flow around a leading edge of a flat plate when vortices with their axes normal to the flat plate surface is carried out to investigate the leading-edge receptivity to the vortical dis...
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Three-dimensional numerical simulation of the flow around a leading edge of a flat plate when vortices with their axes normal to the flat plate surface is carried out to investigate the leading-edge receptivity to the vortical disturbances. It is shown that the vertical vortices outside the boundary layer are not titled and deformed, contradicting to what was reported in previous studies. It is revealed that the streamwise structures, which are dominant in the boundary layer, are formed due to the velocity field induced by the wall-normal vortices outside the boundary layer. It also is found that neighboring pair of vortices side-by-side in the spanwise direction are connected to each other very close to the wall.
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A simple analytical model for leading-edge vortex (LEV) growth is proposed and tested, based on the transport of vorticity-containing mass through the shear-layer. The two-dimensional case is validated using time-resolved Particle...
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A simple analytical model for leading-edge vortex (LEV) growth is proposed and tested, based on the transport of vorticity-containing mass through the shear-layer. The two-dimensional case is validated using time-resolved Particle Image Velocimetry. As a precursor to developing a model for finite wings, the effect of varying spanwise flow on a nominally two-dimensional profile is investigated by imposing plunging and flapping motions on high aspect-ratio flat-plate profiles of sweep angles Λ = +45°, -45° and 0°. By varying sweep angle, both coinciding and opposing gradients of spanwise vorticity stretching and convection were tested. It was shown that nominally two-dimensional spanwise flow has no effect on vortex strength and thus force history for plunging kinematics. However, force histories for flapping kinematics were dependent on sweep angle suggesting that spanwise flow regulates vortex strength when coupled with gradients in effective incidence.
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A review emphasizing the quantitative studies of leading-edge vortices at supersonic speed is presented. While quantitative investigations of vortical flow over delta wings are extensive in the incompressible regime, and to a degr...
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A review emphasizing the quantitative studies of leading-edge vortices at supersonic speed is presented. While quantitative investigations of vortical flow over delta wings are extensive in the incompressible regime, and to a degree in transonic range, their measurements in supersonic freestream are very scarce. It is illustrated that the existing knowledge of leading-edge vortices in the supersonic regime is mainly qualitative, compiled from large amount of flow visualization experiments. A brief account of the flow visualization studies is first presented, followed by a comprehensive survey of the various measurement attempts to quantify these vortices. On the qualitative side, this survey reveals that in spite of the past efforts, the literature still lacks a unified topological description of the compressible leeward vortical Hows. In quantitative investigations, the experience with pressure probes and seed based optical measurement techniques is highlighted, and the associated results summarized. Amongst them, although there exists a topological similarity in the delta wing leeward flow at low- and high-speeds, available measurements suggest that leading-edge vortices in supersonic flow have a very different axial flow character. Additional salient features of leading-edge vortices in supersonic freestreams are also provided in the paper.
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The present article conducted detailed velocity measurements beneath simulated ice blocks with different leading-edge geometries (round, rectangular, upward and downward triangular). The results examined flow separation at the lea...
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The present article conducted detailed velocity measurements beneath simulated ice blocks with different leading-edge geometries (round, rectangular, upward and downward triangular). The results examined flow separation at the leading-edge, vortex generation, and subsequent vortex propagation. The instantaneous velocity field depicts an unsteady flow dominated by large-scale vortices, with the Kelvin-Helmholtz type instability dominating the shear layer interface. The mode of vortex generation and propagation was influenced by the geometry of the leading edge. These vortices were dominant for the rectangular and upward triangular configurations. Propagation of these vortices creates low-pressure zones beneath the simulated ice block, which can atfect the ice block stability. For all ice blocks, the mean flow accelerated, due to flow separation, and this can result in fluctuations in the dynamic pressure field. These events can lead to greater under-turning moments, as well as the interfacial melting of the ice.
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This paper presents an overview of experimental investigations on a 65 deg swept delta wing as part of the International Vortex Flow Experiment 2 (VFE-2). Results obtained in low-speed wind tunnel facilities include oil flow and l...
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This paper presents an overview of experimental investigations on a 65 deg swept delta wing as part of the International Vortex Flow Experiment 2 (VFE-2). Results obtained in low-speed wind tunnel facilities include oil flow and laser light sheet flow visualization, mean and unsteady surface pressure distributions as well as mean and turbulent velocity components of the flow field and close to the wing surface. Thus, field and near wall distributions of all components of the Reynolds stress tensor are available. Details of the delta wing vortex structure and breakdown phenomenon are discussed and analyzed. Vortex bursting leads to specific spectral densities of velocity and surface pressure fluctuations characterized by narrow band distributions associated with the helical mode instability of the vortex breakdown flowfield. Further, special emphasis is on the occurrence of an inner vortex detected for the low Reynolds number and Mach number regime. This inboard vortex results from a laminar separation close to the apex due to the spanwise pressure gradient in the area of relatively large thickness while the classical leading-edge vortex progressing from the rear part to the apex is fed from the turbulent shear layers shed at the wing upper and lower side.
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In recent years, leading-edge tubercles of humpback whales have received increasing attention as a passive stall control mechanism. The control mechanism and flow field structure of a reference (ref) and two modified airfoils (mod...
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In recent years, leading-edge tubercles of humpback whales have received increasing attention as a passive stall control mechanism. The control mechanism and flow field structure of a reference (ref) and two modified airfoils (mod-1 and mod-2) are investigated numerically and experimentally at a Reynolds number of Re = 5 x 105 in this paper. The results demonstrate that the lift coefficient of the modified airfoils is enhanced to a certain extent after these airfoils stall. In addition, the stall processes of mod-2 are smooth and stable over the observed sudden decrease in ref. Counter-rotation vortex pairs (CRVPs), which improves momentum exchange in the trailing edge boundary layer on the suction side, according to streamline slices and iso-surfaces of the vorticity. Moreover, interaction between streamwise vortices is the main reason for the improved hydrodynamic characteristics at high angles of attack (AOAs). Furthermore, when smoke visualization is carried out in a low-Re wind tunnel, mod-1 and mod-2 exhibit similar characteristics, vortex pairs are periodic and symmetric along the wingspan direction at alpha = 5 degrees, and vortex pairs begin to interact and influence flow separation at alpha = 15 degrees. Finally, numerical analysis of the characteristics of tubercle turbines is conducted. The findings reveal that the energy efficiency can be enhanced within a narrow range of tip speed ratios (TSRs).
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The Second International Vortex Flow Experiment provided a variety of experimental data for a 65° swept delta wing sharp and blunt leading edges. Flow details including forces and moments, surface pressures, Pressure Sensitive Pa...
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The Second International Vortex Flow Experiment provided a variety of experimental data for a 65° swept delta wing sharp and blunt leading edges. Flow details including forces and moments, surface pressures, Pressure Sensitive Paint measurements, and off-surface flow variables from Particle Image Velocimetry were made available for comparisons with computational simulations. This paper concentrates on some typical problems of delta wings with rounded leading edges at subsonic speed: the prediction of the main leading edge separation, the generation of the second inner vortex, the effect of transition, and Reynolds number effects.
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To understand the effects of flexibility on aerodynamic force, the lattice Boltzmann flexible particle method (LBFPM) is employed to simulate deformation and its relationship with inertial and elastic forces in a flapping motion o...
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To understand the effects of flexibility on aerodynamic force, the lattice Boltzmann flexible particle method (LBFPM) is employed to simulate deformation and its relationship with inertial and elastic forces in a flapping motion of a chord-wise flexible wing in a three-dimensional space at a hovering Reynolds number of Re = 136. The rigidity El and effective inertia Pi(0) are systematically varied, and lift, drag, deformation and power efficiency are computed and compared. It is found that both the rotational and translational inertia contribute to the deflection limited by flexural rigidity and result in a large angular and translation velocities, which generate a large intensity of vorticity and benefit lift and power efficiency. It is revealed that a "mirrored S" or "S" shaped deflection due to the rotational inertia plays a more positive role than the deflection caused by the translational inertia. (C) 2014 Elsevier Ltd. All rights reserved.
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Leading-edge tubercles on a humpback whale flipper are known to enhance its hydrodynamic performance at post-stall angles of attack (Miklosovic et al 2004 Phys. Fluids 16 39-42). We investigate vortical structures above a three-di...
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Leading-edge tubercles on a humpback whale flipper are known to enhance its hydrodynamic performance at post-stall angles of attack (Miklosovic et al 2004 Phys. Fluids 16 39-42). We investigate vortical structures above a three-dimensional wing with tubercles using surface-oil-flow visualization and particle image velocimetry measurement. Two wing models with and without tubercles, previously studied by Miklosovic et al (2004 Phys. Fluids 16 39-42), are considered at the Reynolds number of 180 000 based on the free-stream velocity and mean chord length. At this Reynolds number, tubercles delay the stall angle by 7 degrees and increase the maximum lift coefficient by about 22%. At a low angle of attack, flow separation first occurs near the tip region for both wing models. While flow separation rapidly progresses inboard (toward the wing root) for the model without tubercles with increasing angle of attack, tubercles produce two types of vortical motions and block the inboard progression of flow separation, resulting in delayed stall from alpha = 8 degrees to 15 degrees. One of these two vortical structures is pairs of counter-rotating streamwise vortices evolving from hemi-spherical separation bubbles near the leading-edge troughs at pre-, near-, and post-stall angles of attack, and the other is asymmetric pairs of streamwise vortices evolving from separated flow regions after the mid-chord region at near-stall angle of attack. At a post-stall angle of attack (alpha = 16 degrees), strong clockwise and counter-clockwise streamwise vortices are generated from foci at the root and tip near the trailing edge, respectively, and delay flow separation in the mid-span, resulting in a higher lift coefficient than that without tubercles.
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A review is presented of the initial experimental results and analysis that formed the basis the Vortex Flow Experiment 2 (VFE-2). The focus of this work was to distinguish the basic effects of Reynolds number, Mach number, angle ...
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A review is presented of the initial experimental results and analysis that formed the basis the Vortex Flow Experiment 2 (VFE-2). The focus of this work was to distinguish the basic effects of Reynolds number, Mach number, angle of attack, and leading-edge bluntness on separation-induced leading-edge vortex flows that are common to slender wings. Primary analysis is focused on detailed static surface pressure distributions, and the results demonstrate significant effects regarding the onset and progression of leading-edge vortex separation.
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