Various aspects of PIV measurements

There are various aspects that should be taken into consideration while doing PIV measurements. Starting from image capturing to ultimately converting the image information into velocity vectors, each step requires proper validation. As already mentioned, the tracer particles should follow the flow faithfully without much velocity lag. Correspondingly, the tracer particles should be homogeneously distributed in the flow field. They should be small enough to follow the fluid movement and large enough to be visible.
A set of six non-dimensional parameters that are most signicant for optimization of PIV measurements were identified by Keane and Adrian (1990). These are the data validation criterion, the particle image density, the relative in-plane image displacement, the relative out-of-plane displacement, a velocity gradient parameter and the ratio of mean image diameter to the interrogation spot diameter. Two terms which are frequently used in PIV measurements are source density

and the image density