Particle image velocimetry (PIV) is a method that is commonly used to visualize the flow of particles in a fluid. PIV is often implemented for research or educational purposes, and allows a scientist to measure the speed and movement of fluids such as water. There are several approaches to particle image velocimetry, and the technique continues to improve as new technology is developed.
To visualize the movement of a fluid, very small particles called "tracers" are introduced into the flow. Due to their small size, these tracer particles behave in a manner that is nearly identical to the fluid being studied. The tracers used in PIV can be illuminated by the scientist, which makes them easily visible. Particle image velocimetry often uses computer software to record and enhance the visible tracers.
A few different tracer particles can be used; small glass beads, aluminum flakes, and droplets of oil are three common materials that can be implemented for this purpose. These tracers reflect light very well, and increase the visibility of a fluid. Light reflections can be studied with the naked eye, or captured by a camera for analysis. While any light source can be sufficient for PIV, a laser is typically used when accuracy is important.
Film photography was the primary method of recording particle movements when PIV was first developed, though the invention of inexpensive digital cameras has rendered the analog approach obsolete. High-resolution digital particle images are now commonplace. Some computer programs are able to automatically recognize and track each tracer in a PIV image, and provide real-time data about a fluid's movement.
Standard particle image velocimetry records the movement of a fluid in two dimensions. Some variations of PIV enhance this capability, and allow three-dimensional visualization. This approach uses two cameras instead of one, and is often called stereoscopic PIV. Using special computer software, the viewpoints from these two cameras are combined to create a new point of view.
Particle image velocimetry has many applications. It is commonly used in the field of aerospace engineering, and allows scientists to see the airflow over an aircraft wing or other control surface. PIV is also used in the healthcare community. The study of fluid movement within the body helps physicians visualize blood circulation, and develop new medical implants. Additionally, biologists sometimes also use particle image velocimetry to study the swimming motion of fish or other sea creatures.