In fluid dynamics

Fluid dynamics

In physics, fluid dynamics is a sub-discipline of fluid mechanics that deals with fluid flow—the natural science of fluids in motion. It has several subdisciplines itself, including aerodynamics and hydrodynamics...

, seeding a flow, or a seeded flow, means to introduce particulates or other foreign substances into an otherwise transparent stream of fluid

Fluid

In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....

. These particulates are generally small enough to be carried by the fluid but large enough to be picked up using a flow visualization

Flow visualization

Flow visualization in fluid dynamics is used to make the flow patterns visible, in order to get a qualitative or quantitative information on them.- Overview :...

 technique, such as particle image velocimetry

Particle image velocimetry

Particle image velocimetry is an optical method of flow visualization used in education and research. It is used to obtain instantaneous velocity measurements and related properties in fluids...

 (PIV). In reference to aerodynamic testing, such as wind tunnel

Wind tunnel

A wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...

testing, water tunnel testing, or any other test investigating the flow of a fluid which may be invisible to the naked eye, seeding a flow is often the only way to take visual measurements. Simple examples of a seeded flow include the introduction of smoke into a low speed wind tunnel to see the general path of the air, or injecting colored dye into a water tunnel to see secondary flow structures such as hairpin vortices.