| Résumé | Particle Image Velocimetry (PIV) is an important technique for measuring velocities within a fluid. The flow through an illuminated plane (or volume) is seeded with small, reflective particles and a sequence of digital photographs is taken. By timing the intervals between photographs to ensure that the same particles are within the measurement space for each exposure, flow vectors can be calculated, once the measurement space has been calibrated. To calculate the velocity vectors, the total image is divided into smaller interrogation windows. The average particle movement within each interrogation window between two successive exposures is calculated. Velocity is determined by dividing the distance moved by the time interval between exposures. In its simplest form, the technique is applied in two dimensions using a single camera, but by using stereo photography, it can be extended to three dimensions. The main advantage of PIV over other measurement methods is that it can determine fluid velocity at all locations within the measurement plane simultaneously instead of having to make separate measurements at a series of different point locations. This is an important feature for analyzing unsteady flow. |
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