The Functional Role of Wing Corrugations in Living Systems

Abstract

Questions concerning the functional role of spanwise wing corrugation in living systems are experimentally investigated. Attention was initially directed to this problem by observation of the irregular shape of many insect wings as well as other studies indicating higher lift on these wings. First, a flow visualization scheme was used to observe and photograph streamlines around two different wing sections. One of these, a sheet metal model with geometry matching that of a butterfly wing, was studied at a chord Reynolds number of 1500 and at a Reynolds number of 80 based on corrugation depth. A steady-state recirculation region near the model leading edge was found, and the separated flow region above this recirculation zone formed a laminar reattachment to the model. A second thicker wing was corrugated on the upper surface. Closed streamlines inside these upper surface corrugations were photographed at Reynolds numbers of 8000 and 3800 based on chord length, and 200 and 90 based on corrugation depth. Reductions in pressures on the corrugated upper wing surface relative to a smooth upper wing surface were then measured.

Feather roughness reduces flow separation during low Reynolds number glides of swifts

“…The upper surface corrugation of swift hand wings resembles the corrugation of dragonfly airfoils, but is concentrated towards the leading edge and has a 5-10 times smaller amplitude (Kesel, 2000;Jongerius and Lentink, 2010;Lentink and de Kat, 2014). Corrugated dragonfly airfoils also generate laminar separation bubbles in the valleys formed by the corrugation (Rees, 1975a;Buckholz, 1986;Lentink and Gerritsma, 2003;Vargas and Mittal, 2004;Kim et al, 2009;Seifert, 2009, 2010;Murphy and Hu, 2010;Hord and Liang, 2012); such effects of corrugation have not been demonstrated before in birds (Elimelech and Ellington, 2013). The similarity in laminar separation bubbles found on dragonfly and swift wings is remarkable, considering dragonflies operate at Re below 10,000 for which experiments show the boundary layer flow remains laminar (Levy and Seifert, 2009), whereas the flow over hummingbird wings at Re=15,000 and α=10 deg can be turbulent in the separated shear layer above the surface (Elimelech and Ellington, 2013).…”

Zerfurchte Flügel und zähe Luft

“…Ortsfeste Wirbel hinter Flügeladern oder in Furchen können den Widerstand herabsetzen, indem sie eine reibungsarme Unterschicht („Rollenlager“) für die Außenströmung bilden und diese stabilisieren (Abbildung ). Bei Windkanaltests wurde hinter den ortsfesten Wirbeln ein Wiederanliegen der bereits abgelösten Strömung beobachtet .…”

“…0,5 bis 1 mm) ist bei V = 5 m/s eine Re‐Zahl von 170–370 zuzuordnen. Untersuchungen haben gezeigt, dass der Leebereich bei dieser Re‐Zahl von stationären Laminarwirbeln ausgefüllt wird (Abbildung , ). Nach Windkanaluntersuchungen halten die stationären Wirbel die Strömung laminar anliegend und erhöhen damit den Auftrieb.…”

Velocity field and parametric analysis of a subsonic, medium-Reynolds number cavity flow

“…• wind transport pollutant in streets surrounded with buildings (Chabni 1997); • cooling systems over integrated circuits made of parallelepipedic electronics components; • door gaps on motor vehicles (Reulet et al 2002); • insect wings with small cavities or riblets on a wing, increasing lift without drag penalty (Buckholz 1986); • hydrodynamic bearings and lubricating systems (Braun et al 1993); • artificial aortic devices or blood aneurysms (Liou and Liao 1997).…”