Table Of content
Spiral shape
Soaring bird in the wind tunnel
Corridor model
Communicating vortex filaments
Conclusion
Attachments
Spiral shape
The multiple, fluid-mechanical vortex coil remains a synthetic construct. Vortex coils are fluidic compositions of coherent vortex filaments with ascribed properties. The physical properties of the vortex filaments derive from their well- defined internal milieu. Spiral vortex formations occur in nature, but they are "made"! They are synthetic in the sense that generating systems exist that generate fluid-mechanical vortex coils.
So far, Lagrangian coherent vortex systems have not had a universal definition in fluid mechanics. This also applies to spiral systems. The first formulations of spiral rotationally coherent vortex systems came from observations of particular fingering of the wing tips of land-soaring birds. The descriptions of multiple vortex coil systems had no relation to the natural habitats of the birds, but were only arranged laboratory experiments in the wind tunnel; it was as if the decoding of bird flight had begun in a hall in the mid-1980s. At least that's how it was seen at the Department of Bionics and Evolutionary Technology at the Technical University of Berlin. Later, technical airfoil models were examined in the wind tunnel and their suitability for generating spiral vortex systems.
illustration not visible in this excerpt
Fig.1: Conditioning of the segmented tip contour of a model wing. Lift L and drag W were measured. After only 27 variation and selection campaigns, the synthetic wing resembles its biological model: the plumage of the land-soaring bird1.
At the beginning of the investigations by Nachtigall (Saarbrücken) and Rechenberg (Berlin), little was known about the very special fluid mechanics of the vortex coil structures and the theory required for this. In Berlin, the first technical laboratory model of the fingered bird's wing was a splitted edge curve contour of a formerly compact model wing that was now slotted at the end of the wing. At that time, all experimenters in Berlin worked primarily with sheet metal (Fig.1), because lead surfaces offered certain creative freedom when constructing fingered model wings.
With an optimization strategy tailored to wind tunnel tests, the glide ratio (cL/cW)2of a slotted and fingered lead wing was improved by about 10% at the TU Berlin in the 1990s compared to its compact initial geometry. Only the preparation of the stork's wing behaved cheaper in the wind tunnel; with its exorbitantly low drag coefficient.
In the case of the lead wing model (Fig. 1), the partial wings or wing tips of the feather fingers form a curved chain of source points. For a long time, this arcshaped arrangement of the source points was considered less productive for wake flow and momentum exchange there. In fact, the geometry of the vortexgenerating system (ellipse or arc) has a great impact on the quality of the vortexspiral system.
In the 1980s, winglets3entered the stage of research institutes and a short time later of the development departments of the aviation industry. Winglets are fixed partial wings on aircraft wings.
Let's briefly discuss which research questions and research results in the 1990s and 2000s advanced the development of aerodynamically approved wings that could actually be used commercially in civil aviation.
The work of Tucker (1993)4is fundamental to the study of the biological system. The ellipse configuration of biological fingers is not recognized here. The model investigations are carried out with geometries according to the arch configuration. Smith and Komerath5et al. publish 2001 results from wind tunnel tests in which the vortex cores of the multiple winglets form a chain (arc configuration). Entz and Correa6et al. find an improvement in lift/drag performance of 12% to 14% for the three-finger case over the closed tip arch on a model wing (arch configuration). A numerical analysis of the triple configuration is described by Thimmegowda7et al. Likewise, arc configurations are investigated by Sevillano8et al. for very small flight aggregates. The vortex system behind winglet configurations is studied by Zang, Wanng and Fu9. Executed constructions are examined by Ning and Kroo10and Merryisha and Rajendran11, as well as by Scholz12for comparison. An experimental comparison between a single and a multi-winglet is made by Balagurumurugan et al13. A numerical model (Fluent) of a mono-winglet is described by Abdelghany et al14. Bird wing-inspired winglets (arc configuration) investigate Hossain, Rahman et al15. Also executed constructions examined Putro and Pitoyo, et al16. The last publication of an arc configuration from the Berlin department of bionics and evolutionary technology comes from Stache (2006)17. It therefore seems permissible to clarify the state of international science in the late 2010s with the arc configuration of the generator system. Recently, a study on biology-inspired multi-winglets by Yussof et al18. (2022) with a 7-fold fingering on the edge arch of a model wing, also in arch configuration.
To date, we only know the impulse effectiveness of spiral arrangements from the few vortex structures that have been experimentally investigated and measured in wind tunnels with precisely this question in mind. Also, we do not know whether the fluid mechanical effects are scalable or not. It can be observed that the impulse induction of Lagrangian coherent vortices in the flow field is cumulative and thus appears to be a conservative phenomenon. Compensations often occur in cumulative processes: physical effects cancel each other out. In this way, an inducing system can couple momentum into the field at the body-fixed, Lagrangen level without this production becoming visible at the Euler level.
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1Based on illustrations from the pool of the department of bionics and evolutionary technology at the Technical University of Berlin; see also: Stache, M.: Evolutionsstrategisches Design von Tragflügelspitzen. DGLR- Jahrbuch, DGLR-2006-200, 2006, pp. 1131-1138
2Gleitzahl eines Tragflügels, Kennwert aus der Aeromechanik (Lilienthal-Beiwert) und berechnet aus gemessenem oder berechneten Widerstandskoeffizienten cW und dem Koeffizienten des fluiddynamischen Auftriebs CL (Lift). Im Falle des antriebslosen Gleitflugs eines Vogels oder eines (Flug-) Modells entspricht die Gleitzahl zugleich dem Verhältnis aus zurückgelegter Wegstrecke und Höhenverlust.
3Winglets (wörtlich: englisch Flügelchen) bzw. Sharklets (Bezeichnung für Winglets bei Airbus), deutsch Flügelohren[1], sind meistens nach oben und seltener nach oben und unten verlängerte Außenflügel an den Enden der Tragflächen von Luftfahrzeugen. Sie sorgen für eine bessere Seitenstabilität, verringern den induzierten Luftwiderstand und verbessern so den Gleitwinkel sowie die Steigzahl bei niedriger Geschwindigkeit. https://de.wikipedia.org/wiki/Winglet
4VANCE A. TUCKER (1993) GLIDING BIRDS: REDUCTION OF INDUCED DRAG BY WING
TIP SLOTS BETWEEN THE PRIMARY FEATHERS. J. exp. Biol. 180, 285-310 (1993)
5M. J. Smith·, N. Komerath+, R. Ames-, O. Wong-, (2001) PERFORMANCE ANALYSIS OF A WING WITH MULTIPLE WINGLETS; School of Aerospace Engineering, Georgia Institute of Technology, Atlanta, Georgia and J. Pearson, Star Technology and Research, Inc., Mount Pleasant, South Carolina.
6Cosin, R. , Catalano, F.M. , Correa, L.G.N. , Entz, R.M.U. (2010) AERODYNAMIC ANALYSIS OF MULTI-WINGLETS FOR LOW SPEED AIRCRAFT Engineering School of Sao Carlos - University of Sao Paulo.
7Hariprasad Thimmegowda (2016) Computational and Experimental Analysis of Multi-Winglet at Low Subsonic Speed Conference Paper · August 2016
8A. A. Rodríguez Sevillano *, R. Bardera Mora **, M.A. Barcala Montejano*, E. Barroso Barderas ** and I. Díez Arancibia *. (2019) Design of Multiple Winglets for Enhancing Aerodynamics in a Micro Air Vehicle. 8TH EUROPEAN CONFERENCE FOR AERONAUTICS AND SPACE SCIENCES (EUCASS)
9Zang, Wang und Fu (2019) GENERATION MECHANISM AND REDUCTION METHOD OF INDUCED DRAG PRODUCED BY INTERACTING WINGTIP VORTEX SYSTEM. School of Aerospace Engineering Tsinghua University, Beijing, China
10Andrew Ning, Ilan Kroo (2010) Multidisciplinary Considerations in the Design of Wings and Wing Tip Devices. Brigham Young University - Provo, and Stanford University
11Samuel Merryisha1, Parvathy Rajendran (2019) Review of Winglets on Tip Vortex, Drag and Airfoil Geometry School of Aerospace Engineering, Universiti Sains Malaysia, Engineering Campus. Journal of Advanced Research in Fluid Mechanics and Thermal Sciences 63, Issue 2 (2019) 218-237
12Scholz, D. (2018) Definition and discussion of the intrinsic efficiency of winglets, Aircraft Design and Systems Group (AERO), Hamburg University of Applied Sciences; Aerospace Europe CEAS 2017 Conference, 16th-20th October 2017, Palace of the Parliament, Bucharest, Romania, Technical session Aircraft and Spacecraft Design
13R. Balagurumurugan, A.Yadav, A. Ahmed R, S. Narayanan S (2016) Experimental study of single and multiwinglets. Article in Advances and Applications in Fluid Mechanics · April 2016.
14E. S. Abdelghany , E. E. Khalil, O. E. Abdellatif and G. ElHarriri (2016) WINGLET CANT AND SWEEP ANGLES EFFECT ON AIRCRAFT WING PERFORMANCE in Proceedings of the 17 MP 258 th Int. AMME Conference, 19-21 April, 2016
15Altab Hossain, Ataur Rahman, A.K.M. P. Iqbal, M. Ariffin, and M. Mazian (2011) Drag Analysis of an Aircraft Wing Model with and without Bird Feather like Winglet, World Academy of Science, Engineering and Technology, International Journal of Aerospace and Mechanical Engineering. Vol:5, No:9, 2011
16S H S Putro, B J Pitoyo, N Pambudiyatno, Sutardi, and W A Widodo (2020) Comparison of the winglet aerodynamic performance in unmanned aerial vehicle at low Reynolds number. IOP Conf. Series: Materials Science and Engineering 1173 (2021) 012002 2
17Stache, M.(2006): Evolutionsstrategisches Design von Tragflügelspitzen. DGLR- Jahrbuch, DGLR-2006-200, 2006, pp. 1131-1138.
18Hamid Yusoff, Koay Mei Hyie,*, Halim Ghaffar, Aliff Farhan Mohd Yamin, Muhammad Ridzwan Ramli, Wan Mazlina Wan Mohamed, Siti Nur Amalina Mohd Halidi (2022): The Evolution of Induced Drag of Multi-Winglets for Aerodynamic Performance of NACA23015, Journal of Advanced Research in Fluid Mechanics and Thermal Sciences 93, Issue 2 (2022) 100-110.
