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{{Short description|Visualization technique in fluid dynamics}}
{{More footnotes|date=April 2009}}

[[File:Cessna 182 model-wingtip-vortex.jpg|thumb|320px|A model [[Cessna]] with helium-filled bubbles showing [[Streamlines, streaklines and pathlines|pathlines]] of the [[wingtip vortices]].]]

'''Flow visualization''' or '''flow visualisation''' in [[fluid dynamics]] is used to make the [[fluid flow|flow]] patterns visible, in order to get qualitative or quantitative information on them.

== Overview ==
Flow visualization is the art of making flow patterns visible. Most [[fluids]] (air, water, etc.) are [[Transparency (optics)|transparent]], thus their flow patterns are invisible to the naked eye without methods to make them this visible.

Historically, such methods included experimental methods. With the development of computer models and [[Computational fluid dynamics|CFD]] simulating flow processes (e.g. the distribution of air-conditioned air in a new car), purely computational methods have been developed.

== Methods of visualization ==
[[File:shadowgram-gas-grill.jpg|thumb|[[Shadowgraph]] of the turbulent [[Plume (fluid dynamics)|plume]] of hot air rising from a home-barbecue gas grill. Photograph by Gary S. Settles, Floviz Inc.]]
In [[experimental fluid dynamics]], flows are visualized by three methods:
* Surface flow visualization: This reveals the flow [[Streamlines, streaklines and pathlines|streamlines]] in the limit as a solid surface is approached. Colored oil applied to the surface of a [[wind tunnel]] model provides one example (the oil responds to the surface [[shear stress]] and forms a pattern).
* Particle tracer methods: Particles, such as smoke or [[microspheres]], can be added to a flow to trace the fluid motion. We can illuminate the particles with a sheet of [[laser]] light in order to visualize a slice of a complicated fluid flow pattern. Assuming that the particles faithfully follow the streamlines of the flow, we can not only visualize the flow but also measure its velocity using the [[particle image velocimetry]] or [[particle tracking velocimetry]] methods. Particles with densities that match that of the fluid flow will exhibit the most accurate visualization.<ref>http://microspheres.us/fluorescent-microspheres/piv-seeding-microparticle-flow-visualization/599.html PIV seeding particle recommendations</ref>
* Optical methods: Some flows reveal their patterns by way of changes in their optical [[refractive index]]. These are visualized by optical methods known as the [[shadowgraph]], [[schlieren photography]], and [[interferometry]]. More directly, dyes can be added to (usually liquid) flows to measure concentrations; typically employing the [[light attenuation]] or [[laser-induced fluorescence]] techniques.
In [[scientific visualization]] flows are visualized with two main methods:
* Analytical methods that analyse a given flow and show properties like [[streamlines, streaklines, and pathlines]]. The flow can either be given in a finite representation or as a smooth function.
* [[Texture advection]] methods that "bend" textures (or images) according to the flow. As the image is always finite (the flow through could be given as a smooth function), these methods will visualize approximations of the real flow.

== Application ==
In [[computational fluid dynamics]] the numerical solution of the governing equations can yield all the fluid properties in space and time. This overwhelming amount of information must be displayed in a meaningful form. Thus flow visualization is equally important in computational as in experimental fluid dynamics.

== See also ==
{{Div col|colwidth=20em}}
* [[Elementary flow]]
* [[Image-based flow visualization]]
* [[Lagrangian–Eulerian advection]]
* [[Rheoscopic fluid]]
* [[Scientific visualization]]
* [[Skin friction lines]]
* [[Streamlet (scientific visualization)]]
* [[Streamlines, streaklines and pathlines]]
* [[Streamsurface]]
* [[Tensor glyph]]
* [[Texture advection]]
* [[Vortex core line]]
{{Div col end}}

== References ==

* {{cite book |last=Merzkirch | first=W. |title=Flow visualization |location=New York | publisher=Academic Press |year=1987 |isbn=0-12-491351-2}}
* {{cite book |author-link=Milton Van Dyke |last=Van Dyke | first=M. |title=[[An album of fluid motion]] |location= Stanford, CA |publisher=Parabolic Press |year=1982 |isbn=0-915760-03-7}}
* {{cite book |last1=Samimy |first1=M. | last2=Breuer |first2=K. S. |last3=Leal |first3=L. G. |last4=Steen |first4=P. H. |title=A gallery of fluid motion |publisher=Cambridge University Press |year=2004 |isbn=0-521-82773-6}}
* {{cite book |last=Settles |first=G. S. |title=Schlieren and shadowgraph techniques: Visualizing phenomena in transparent media |location=Berlin |publisher=Springer-Verlag |year=2001 |isbn=3-540-66155-7}}
* {{cite book |last1=Smits |first1=A. J. |last2=Lim |first2=T. T. |title=Flow visualization: Techniques and examples |publisher=Imperial College Press |year=2000 |isbn=1-86094-193-1}}
{{Reflist}}

== External links ==
{{Commons category|Flow visualization}}
*[http://www.cg.tuwien.ac.at/~helwig/diss/node10.htm Flow visualization techniques].
*[https://web.archive.org/web/20070928023426/https://visualization.hpc.mil/wiki/index.php/Visualization_Algorithms Flow visualization algorithms].
*[http://www.flowvis.org Gallery of Flow Visualization Examples.]
*[https://web.archive.org/web/20080307024636/http://www.interactiveflows.com/links/ Educational Particle Image Velocimetry (e-PIV) - resources and demonstrations]

{{Visualization}}

[[Category:Flow visualization| ]]

Flow visualization - Revision history

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