Particle Image Velocimetry

The Particle Image Velocimetry (PIV) is a modern nonintrusive laseroptical principle to measure planar two- or three-component velocity fields. However, the principle of observing the shift of tracer particles in a fluid and measuring the time between the particle observations is known since long times. A typical PIV-System consists of a laser-light source, at least one camera, some electronics for signal processing and a PC. For a measurement, the light of the two laser pulses from the double-pulse laser is extended to a planar laser-light sheet. The laserlight sheet describes the measuring plane by illuminating the tracer particles, which are following the flow, within this area. The light is backscattered by the process of Mie-Scattering and detected by a special PIV-CCD-Camera that allows the detection two images with a delay of only few microseconds. The two Images than are analysed by using cross correlation techniques or Tracking Algorithms for the particles (Particle Tracking Velocimetry, PTV). This way a large number of two component velocity vector within the 2-dimensional light sheet can be measured with a single sequence. By using two cameras this measuring system can be used to measure all three components of the velocity vector within the 2-dimensional measuring plane. PIV is used to get an idea of the flow. By realizing longer measuring sequences, the mean velocity field but also turbulence and the spatial derivations can be determined. The typical sampling rate is about 10 to 30 Hz or lower but can be pushed to up to 100 kHz.