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Jet propulsion

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Jet propulsion is motion produced by passing a jet of matter (typically air or water) in the opposite direction to the direction of motion. By conservation of momentum, the moving body is propelled in the opposite direction to the jet.

A number of animals, including cephalopods, sea hares, arthropods and fish have convergently evolved jet propulsion mechanisms. This is most commonly used in the jet engine, but is also the means of propulsion utilized by NASA to power various space craft.

Physics

Jet propulsion is most effective when the Reynolds number is high - that is, the object being propelled is relatively large and passing through a low-viscosity medium.[1]

In biology, the most efficient jets are pulsed, rather than continuous:[2] at least when the Reynolds number is greater than 6.[3]

Jet engine

Main article: Jet engine

A jet engine is a reaction engine that discharges a fast moving jet of fluid to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets and pump-jets. In general, most jet engines are internal combustion engines[4] but non-combusting forms also exist.

Jet-propelled animals

Further information: Aquatic locomotion § Jet Propulsion

Jet propulsion in cephalopods is produced by water being exhaled through a siphon, which typically narrows to a small opening to produce the maximum exhalent velocity. The water passes through the gills prior to exhalation, fulfilling the dual purpose of respiration and locomotion.[1] Sea hares (gastropod molluscs) employ a similar means of jet propulsion, but without the sophisticated neurological machinery of cephalopods they navigate somewhat more clumsily.[1]

Some teleost fish have also developed jet propulsion, passing water through the gills to supplement fin-driven motion.[5]: 201 

In some dragonfly larvae, jet propulsion is achieved by the expulsion of water from a specialised cavity through the anus. Given the small size of the organism, a great speed is achieved.[6]

Scallops and cardiids,[7] siphonophores,[8] tunicates (such as salps),[9][10] and some jellyfish[11][12][13] also employ jet propulsion. The most efficient jet-propelled organisms are the salps,[9] which use an order of magnitude less energy (per kilogram per metre) than squid.[14]

References

  1. ^ a b c Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi: 10.1111/j.1469-185X.1972.tb00975.x , please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi= 10.1111/j.1469-185X.1972.tb00975.x instead.
  2. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1242/jeb.041962, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1242/jeb.041962 instead.
  3. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1098/rspb.2005.3109, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1098/rspb.2005.3109 instead.
  4. ^ Encyclopædia Britannica. "Encyclopædia Britannica: Internal Combustion Engine". Britannica.com. Retrieved 2010-03-26.{{cite web}}: CS1 maint: multiple names: authors list (link)
  5. ^ Wake, M.H. (1993). "The Skull as a Locomotor Organ". In Hanken, James (ed.). The Skull. University of Chicago Press. p. 460. ISBN 978-0-226-31573-7.
  6. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1007/BF00631969 , please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1007/BF00631969 instead.
  7. ^ Chamberlain Jr, John A. (1987). "32. Locomotion of Nautilus". In Saunders, W. B.; Landman, N. H. (eds.). Nautilus: The Biology and Paleobiology of a Living Fossil. ISBN 9789048132980.
  8. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1017/S0025315400057271 , please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1017/S0025315400057271 instead.
  9. ^ a b Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1111/j.1469-7998.1983.tb05071.x, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1111/j.1469-7998.1983.tb05071.x instead.
  10. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1016/0022-0981(84)90059-5, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1016/0022-0981(84)90059-5 instead.
  11. ^ http://jeb.biologists.org/cgi/content/abstract/134/1/313. {{cite journal}}: Cite journal requires |journal= (help); Missing or empty |title= (help)
  12. ^ http://jeb.biologists.org/cgi/content/abstract/134/1/333. {{cite journal}}: Cite journal requires |journal= (help); Missing or empty |title= (help)
  13. ^ http://jeb.biologists.org/cgi/content/abstract/134/1/347. {{cite journal}}: Cite journal requires |journal= (help); Missing or empty |title= (help)
  14. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1139/z90-111, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1139/z90-111 instead.
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