Editing Fin (section)

==Thrust generation==
Foil shaped fins generate [[thrust]] when moved, the lift of the fin sets water or air in motion and pushes the fin in the opposite direction. Aquatic animals get significant [[thrust]] by moving fins back and forth in water. Often the [[Caudal fin|tail fin]] is used, but some aquatic animals generate thrust from [[pectoral fins]].<ref name=Sfakiotakis /> Fins can also generate thrust if they are rotated in air or water. [[Turbine]]s and [[propeller]]s (and sometimes [[Mechanical fan|fans]] and [[pump]]s) use a number of rotating fins, also called foils, wings, arms or blades.  Propellers use the fins to translate torquing force to lateral thrust, thus propelling an aircraft or ship.<ref>Carlton, John (2007) [https://books.google.com/books?id=QrLNCxzynU4C ''Marine Propellers and Propulsion''] Pages 1–28, Butterworth-Heinemann. {{ISBN|9780750681506}}.</ref> Turbines work in reverse, using the lift of the blades to generate torque and power from moving gases or water.<ref>Soares, Claire (2008) [https://books.google.com/books?id=rTPZp1YCQBkC ''Gas Turbines: A Handbook of Air, Land, and Sea Applications''] {{Webarchive|url=https://web.archive.org/web/20231216095310/https://books.google.com/books?id=rTPZp1YCQBkC |date=2023-12-16 }} Pages 1–23, Butterworth-Heinemann. {{ISBN|9780750679695}}.</ref>

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| header            = Moving fins can provide thrust
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| image1            = Barb gonio 080525 9610 ltn Cf.jpg
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| caption1          = Fish get thrust moving vertical tail fins from side to side.
| image2            = Southern right whale caudal fin-2 no sky.JPG
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| caption2          = [[Cetacean]]s get thrust moving horizontal tail fins up and down.
| image3            = Dasyatis thetidis.jpg
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| caption3          = Stingrays get thrust from large pectoral fins.
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{{multiple image
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| image1            = Stern of Bro Elisabeth 2.jpg
| width1            = 141
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| caption1          = Ship propeller
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| width2            = 140
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| caption2          = Airplane propeller
| image3            = MAKS-2007-turbine.JPG
| width3            = 156
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| caption3          = Compressor fins (blades)
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| image1            = Cavitation Propeller Damage.JPG
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| caption1          = Cavitation damage is evident on this propeller.
| image2            = Thunnus obesus (Bigeye tuna) diagram cropped.GIF
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| caption2          = {{center|<small>Drawing by Dr Tony Ayling</small><hr />[[Finlet]]s may influence the way a [[vortex]] develops around the tail fin.}}
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[[Cavitation]] can be a problem with high power applications, resulting in damage to propellers or turbines, as well as noise and loss of power.<ref name=Franc>Franc, Jean-Pierre and Michel, Jean-Marie (2004) [https://books.google.com/books?id=QJOQYa_oo24C ''Fundamentals of Cavitation''] {{Webarchive|url=https://web.archive.org/web/20231216095310/https://books.google.com/books?id=QJOQYa_oo24C |date=2023-12-16 }} Springer. {{ISBN|9781402022326}}.</ref> Cavitation occurs when negative pressure causes bubbles (cavities) to form in a liquid, which then promptly and violently collapse. It can cause significant damage and wear.<ref name=Franc /> Cavitation damage can also occur to the tail fins of powerful swimming marine animals, such as dolphins and tuna. Cavitation is more likely to occur near the surface of the ocean, where the ambient water pressure is relatively low. Even if they have the power to swim faster, dolphins may have to restrict their speed because collapsing cavitation bubbles on their tail are too painful.<ref name=hurts>{{cite magazine | last = Brahic | first = Catherine | title = Dolphins swim so fast it hurts | magazine = New Scientist | date = 2008-03-28 | url = https://www.newscientist.com/channel/life/dn13553-dolphins-swim-so-fast-it-hurts.html | access-date = 2008-03-31 | archive-date = 2020-11-09 | archive-url = https://web.archive.org/web/20201109040122/https://www.newscientist.com/article/dn13553-dolphins-swim-so-fast-it-hurts/?ignored=irrelevant | url-status = live }}</ref> Cavitation also slows tuna, but for a different reason. Unlike dolphins, these fish do not feel the bubbles, because they have bony fins without nerve endings. Nevertheless, they cannot swim faster because the cavitation bubbles create a vapor film around their fins that limits their speed. Lesions have been found on tuna that are consistent with cavitation damage.<ref name=hurts/>

[[Scombrid]] fishes (tuna, mackerel and bonito) are particularly high-performance swimmers. Along the margin at the rear of their bodies is a line of small rayless, non-retractable fins, known as [[finlet]]s. There has been much speculation about the function  of these finlets. Research done in 2000 and 2001 by Nauen and Lauder indicated that "the finlets have a hydrodynamic effect on local flow during steady swimming" and that "the most posterior finlet is oriented to redirect flow into the developing tail vortex, which may increase thrust produced by the tail of swimming mackerel".<ref>{{cite journal | last1 = Nauen | first1 = JC | last2 = Lauder | first2 = GV | year = 2001a | title = Locomotion in scombrid fishes: visualization of flow around the caudal peduncle and finlets of the Chub mackerel ''Scomber japonicus'' | url = http://jeb.biologists.org/content/204/13/2251.long | journal = Journal of Experimental Biology | volume = 204 | issue = 13 | pages = 2251–63 | doi = 10.1242/jeb.204.13.2251 | pmid = 11507109 | bibcode = 2001JExpB.204.2251N | access-date = 2012-11-20 | archive-date = 2020-08-07 | archive-url = https://web.archive.org/web/20200807052800/http://jeb.biologists.org/content/204/13/2251.long | url-status = live | url-access = subscription }}</ref><ref>{{cite journal | last1 = Nauen | first1 = JC | last2 = Lauder | first2 = GV | year = 2001b | title = Three-dimensional analysis of finlet kinematics in the Chub mackerel ''(Scomber japonicus)'' | journal = The Biological Bulletin | volume = 200 | issue = 1 | pages = 9–19 | doi = 10.2307/1543081 | pmid = 11249216 | jstor = 1543081 | s2cid = 28910289 | url = https://www.biodiversitylibrary.org/part/10992 | access-date = 2021-05-19 | archive-date = 2020-06-14 | archive-url = https://web.archive.org/web/20200614084947/https://www.biodiversitylibrary.org/part/10992 | url-status = live }}</ref><ref>{{cite journal | last1 = Nauen | first1 = JC | last2 = Lauder | first2 = GV | year = 2000 | title = Locomotion in scombrid fishes: morphology and kinematics of the finlets of the Chub mackerel ''Scomber japonicus'' | url = http://jeb.biologists.org/content/203/15/2247.full.pdf | journal = Journal of Experimental Biology | volume = 203 | issue = 15 | pages = 2247–59 | doi = 10.1242/jeb.203.15.2247 | pmid = 10887065 | bibcode = 2000JExpB.203.2247N | access-date = 2012-11-20 | archive-date = 2020-10-01 | archive-url = https://web.archive.org/web/20201001091120/http://jeb.biologists.org/content/203/15/2247.full.pdf | url-status = live }}</ref>

Fish use multiple fins, so it is possible that a given fin can have a hydrodynamic interaction with another fin. In particular, the fins immediately upstream of the caudal (tail) fin may be proximate fins that can directly affect the flow dynamics at the caudal fin. In 2011, researchers using [[Particle image velocimetry|volumetric imaging]] techniques were able to generate "the first instantaneous three-dimensional views of wake structures as they are produced by freely swimming fishes". They found that "continuous tail beats resulted in the formation of a linked chain of vortex rings" and that "the dorsal and anal fin wakes are rapidly entrained by the caudal fin wake, approximately within the timeframe of a subsequent tail beat".<ref>{{cite journal | last1 = Flammang | first1 = BE | last2 = Lauder | first2 = GV | last3 = Troolin | first3 = DR | last4 = Strand | first4 = TE | year = 2011 | title = Volumetric imaging of fish locomotion | url = http://intl-rsbl.royalsocietypublishing.org/content/7/5/695.full | journal = Biology Letters | volume = 7 | issue = 5 | pages = 695–698 | doi = 10.1098/rsbl.2011.0282 | pmid = 21508026 | pmc = 3169073 | access-date = 2012-11-21 | archive-date = 2016-03-04 | archive-url = https://web.archive.org/web/20160304031235/http://intl-rsbl.royalsocietypublishing.org/content/7/5/695.full | url-status = live }}</ref>

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