The development of PIV can be traced back to the early 20th century when researchers started exploring different methods to visualize and measure fluid flow. PIV has found widespread applications in various fields of science and engineering, including aerodynamics, combustion, oceanography, and biofluids. Particle image velocimetry (PIV) is a non-intrusive optical flow measurement technique used to study fluid flow patterns and velocities. PIV software is used to post-process the optical images. A fiber-optic cable or liquid light guide may connect the laser to the lens setup. Typical PIV apparatus consists of a camera (normally a digital camera with a CCD chip in modern systems), a strobe or laser with an optical arrangement to limit the physical region illuminated (normally a cylindrical lens to convert a light beam to a line), a synchronizer to act as an external trigger for control of the camera and laser, the seeding particles and the fluid under investigation. When the particle concentration is so low that it is possible to follow an individual particle it is called particle tracking velocimetry, while laser speckle velocimetry is used for cases where the particle concentration is so high that it is difficult to observe individual particles in an image. During PIV, the particle concentration is such that it is possible to identify individual particles in an image, but not with certainty to track it between images. The main difference between PIV and those techniques is that PIV produces two-dimensional or even three-dimensional vector fields, while the other techniques measure the velocity at a point. Other techniques used to measure flows are laser Doppler velocimetry and hot-wire anemometry. The motion of the seeding particles is used to calculate speed and direction (the velocity field) of the flow being studied. The fluid with entrained particles is illuminated so that particles are visible. The fluid is seeded with tracer particles which, for sufficiently small particles, are assumed to faithfully follow the flow dynamics (the degree to which the particles faithfully follow the flow is represented by the Stokes number). It is used to obtain instantaneous velocity measurements and related properties in fluids. Particle image velocimetry ( PIV) is an optical method of flow visualization used in education and research.
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