Rival, David Emory (2009)
Development, Control and Recovery of Leading- and Trailing-Edge Vortices in Tandem-Airfoil Configurations.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung
Kurzbeschreibung (Abstract)
Particle Image Velocimetry (PIV) has been used to uncover the two distinct aerodynamic mechanisms associated with cruise and hover conditions in tandem-airfoil configurations, i.e. dragonfly flight. The studies performed here have been carried out at transitional Reynolds numbers and reduced frequencies corresponding to dragonfly flight, which in turn are relevant to the development of Micro Air Vehicles (MAVs). The associated vortex dynamics of these strongly separated flows have been examined using vortex-tracking, pressure-integration and control-volume methods. To a lesser extent, direct force measurements and URANS-based numerical simulations have been used to support the findings. At first the formation and manipulation of leading-edge vortices (LEVs) and trailing-edge vortices (TEVs) for a single airfoil have been examined using non-sinusoidal kinematics and the theory of optimal vortex formation. Results show that the development of the LEV can be modified without the need for a span-wise flow, contrary to popular belief. In a similar fashion, the TEV can be reduced or even completely mitigated through the superposition of a quick-pitch motion near the bottom of the stroke. Subsequently, the studies of tandem configurations in cruise conditions revealed that the vortex-formation process for the forefoil is strongly influenced by the placement of a hindfoil in its wake, be it static or moving. In strong agreement with observations made on live dragonflies, airfoil configurations with specific out-of-phase kinematics of approximately ψ=60° were found to generate net thrust. The mechanism for this thrust production was identified as the formation of a leading-edge suction bubble on the hindfoil induced by the passing of the forefoil LEV. Similarly, the passing forefoil TEV was found to induce a vortex on the hindfoil, which in turn helped reduce power consumption on the upstroke. Finally, time-resolved PIV investigations into tandem hovering identified a beneficial interaction at ψ=90° in which the forefoil TEV interacted with the development of the hindfoil LEV. This aerodynamic mechanism in turn adjusted the strength and positioning of the hindfoil TEV, thus affecting thrust and power consumption. This result agrees with observations in nature and analogous force measurements for three-dimensional flapping wings, suggesting again that a span-wise flow is not necessarily a requirement for efficient vortex control but rather a result of the evolutionary restrictions in nature towards root-flapping flight.
Typ des Eintrags: | Dissertation | ||||
---|---|---|---|---|---|
Erschienen: | 2009 | ||||
Autor(en): | Rival, David Emory | ||||
Art des Eintrags: | Erstveröffentlichung | ||||
Titel: | Development, Control and Recovery of Leading- and Trailing-Edge Vortices in Tandem-Airfoil Configurations | ||||
Sprache: | Englisch | ||||
Referenten: | Tropea, Professor Cameron ; Radespiel, Professor Rolf | ||||
Publikationsjahr: | 21 Oktober 2009 | ||||
Ort: | Darmstadt | ||||
Verlag: | Technische Universität | ||||
Datum der mündlichen Prüfung: | 14 Oktober 2009 | ||||
URL / URN: | urn:nbn:de:tuda-tuprints-19290 | ||||
Kurzbeschreibung (Abstract): | Particle Image Velocimetry (PIV) has been used to uncover the two distinct aerodynamic mechanisms associated with cruise and hover conditions in tandem-airfoil configurations, i.e. dragonfly flight. The studies performed here have been carried out at transitional Reynolds numbers and reduced frequencies corresponding to dragonfly flight, which in turn are relevant to the development of Micro Air Vehicles (MAVs). The associated vortex dynamics of these strongly separated flows have been examined using vortex-tracking, pressure-integration and control-volume methods. To a lesser extent, direct force measurements and URANS-based numerical simulations have been used to support the findings. At first the formation and manipulation of leading-edge vortices (LEVs) and trailing-edge vortices (TEVs) for a single airfoil have been examined using non-sinusoidal kinematics and the theory of optimal vortex formation. Results show that the development of the LEV can be modified without the need for a span-wise flow, contrary to popular belief. In a similar fashion, the TEV can be reduced or even completely mitigated through the superposition of a quick-pitch motion near the bottom of the stroke. Subsequently, the studies of tandem configurations in cruise conditions revealed that the vortex-formation process for the forefoil is strongly influenced by the placement of a hindfoil in its wake, be it static or moving. In strong agreement with observations made on live dragonflies, airfoil configurations with specific out-of-phase kinematics of approximately ψ=60° were found to generate net thrust. The mechanism for this thrust production was identified as the formation of a leading-edge suction bubble on the hindfoil induced by the passing of the forefoil LEV. Similarly, the passing forefoil TEV was found to induce a vortex on the hindfoil, which in turn helped reduce power consumption on the upstroke. Finally, time-resolved PIV investigations into tandem hovering identified a beneficial interaction at ψ=90° in which the forefoil TEV interacted with the development of the hindfoil LEV. This aerodynamic mechanism in turn adjusted the strength and positioning of the hindfoil TEV, thus affecting thrust and power consumption. This result agrees with observations in nature and analogous force measurements for three-dimensional flapping wings, suggesting again that a span-wise flow is not necessarily a requirement for efficient vortex control but rather a result of the evolutionary restrictions in nature towards root-flapping flight. |
||||
Alternatives oder übersetztes Abstract: |
|
||||
Sachgruppe der Dewey Dezimalklassifikatin (DDC): | 600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften und Maschinenbau | ||||
Fachbereich(e)/-gebiet(e): | 16 Fachbereich Maschinenbau > Fachgebiet Strömungslehre und Aerodynamik (SLA) 16 Fachbereich Maschinenbau |
||||
Hinterlegungsdatum: | 23 Okt 2009 09:27 | ||||
Letzte Änderung: | 05 Mär 2013 09:28 | ||||
PPN: | |||||
Referenten: | Tropea, Professor Cameron ; Radespiel, Professor Rolf | ||||
Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: | 14 Oktober 2009 | ||||
Export: | |||||
Suche nach Titel in: | TUfind oder in Google |
Frage zum Eintrag |
Optionen (nur für Redakteure)
Redaktionelle Details anzeigen |