Investigation of three-dimensional flow structure on maneuvering finite-span wings
Başlık çevirisi mevcut değil.
- Tez No: 400725
- Danışmanlar: PROF. DR. DONALD ROCKWELL
- Tez Türü: Doktora
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2012
- Dil: İngilizce
- Üniversite: Lehigh University
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 198
Özet
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Özet (Çeviri)
The three-dimensional, unsteady flow structure on low aspect ratio wings arising from plunging and pitch-up motions is addressed via a technique of stereoscopic particle image velocimetry (SPIV), which yields characterization of the three-dimensional flow structure. The time evolution of complex vortex systems is interpreted in terms of phase-referenced three-dimensional streamline patterns, volume images of iso-Q, stacked contours of surface-normal vorticity and spanwise velocity, and vorticity projections in orthogonal directions. In addition to quantitative imaging, a technique of flow (dye) visualization is employed to reveal the major features of the flow structure. Unsteady plunging (heaving) of a wing in the form of a flat plate, over a period corresponding to 3.16 convective time scales C/U, and at a Reynolds number based on chord of 10,000, can give rise to pronounced axial flow in the small-scale leadingedge vortex during its initial stage of formation. Opposing axial flows along the vortex interact at the plane of symmetry, giving rise to large-scale patterns of streamwise2 oriented vorticity, which can dominate the tip vortices over part of the oscillation cycle. Pitch-up (linear ramp-like) motion of wings involves flat plates of various configurations. The pitch-up maneuver is from 0° and 45° over a time span corresponding to four convective time scales, at a Reynolds number based on chord of 10,000. Four different configurations of planforms are employed to investigate the onset and development of the three-dimensionality of the flow structure. Dye visualization reveals effects of variation of the dimensionless pitch rate K on the development of the flow structure during the maneuver. Volumes of constant magnitude of the second invariant of the velocity gradient tensor are interpreted in conjunction with three-dimensional streamline patterns and vorticity projections in orthogonal directions. During the pitch-up motion, the ordered vortical structures are a strong function of wing planform. After attainment of the maximum angle of attack, however, the vortex system has a similar form for extreme configurations of wing planforms. Near the plane of symmetry, a large-scale region of predominantly spanwise vorticity dominates. Away from the plane of symmetry, the flow is dominated by two extensive regions of surface-normal vorticity, i.e., swirl patterns parallel to the wing surface. Finally, dye visualization is employed to reveal the formation and subsequent evolution of leading-edge vortices and related vortical structures for various configurations of pitching and plunging low aspect ratio plates, including the effects of wing geometry, Reynolds number, pitch-axis location, and ramp rate. All cases of the 3 rectangular planform involve a leading-edge vortex with pronounced axial flow, which leads to formation of three-dimensional flow structures, culminating in a large vortical structure centered at the plane of symmetry of the wing. Pitch is also compared to plunge, whereby the functional form of the plunging motion provides an equivalent variation of angle of attack with time that matches the pitching motion. At successively increasing values of time, represented by the convective time scale C/U, the three-dimensional patterns of the flow structure are remarkably similar for the pitching and plunging motions. The similarity of these patterns persists, though they are shifted in time, for variation of either the location of the pitching axis or the dimensionless pitch rate.
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