Skip to main content
Select Source:

Reynolds number

Reynolds number [for Osborne Reynolds], dimensionless quantity associated with the smoothness of flow of a fluid. It is an important quantity used in aerodynamics and hydraulics. At low velocities fluid flow is smooth, or laminar, and the fluid can be pictured as a series of parallel layers, or lamina, moving at different velocities. The fluid friction between these layers gives rise to viscosity. As the fluid flows more rapidly, it reaches a velocity, known as the critical velocity, at which the motion changes from laminar to turbulent (see turbulence), with the formation of eddy currents and vortices that disturb the flow. The Reynolds number for the flow of a fluid of density ρ and viscosity η through a pipe of inside diameter d is given by Rdv/η, where v is the velocity. The Reynolds number for laminar flow in cylindrical pipes is about 1,000.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Reynolds number." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 26 May. 2018 <http://www.encyclopedia.com>.

"Reynolds number." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (May 26, 2018). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/reynolds-number

"Reynolds number." The Columbia Encyclopedia, 6th ed.. . Retrieved May 26, 2018 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/reynolds-number

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Reynolds number

Reynolds number A dimensionless number expressing the balance of viscous and interstitial forces on a small element of moving fluid. The transition from laminar to turbulent flow depends on the Reynolds number (R) which is equal to ρvd/η, where ρ is the fluid density, v the fluid velocity, d the diameter of the pore space through which flow occurs, and η the viscosity. For laminar flow, the Reynolds number is less than 500, while turbulent flow occurs when R is greater than 1000. Darcy's Law for groundwater flow is valid for values of R less than about 1–10.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Reynolds number." A Dictionary of Earth Sciences. . Encyclopedia.com. 26 May. 2018 <http://www.encyclopedia.com>.

"Reynolds number." A Dictionary of Earth Sciences. . Encyclopedia.com. (May 26, 2018). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/reynolds-number

"Reynolds number." A Dictionary of Earth Sciences. . Retrieved May 26, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/reynolds-number

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.