Synthetic Images
Particle Density
The particle density describes the number of particles in the image area. Particle density is a balance between allowing each particle image to be distinct, while providing enough particles for the correlations to remain valid. To demonstrate this, Figure 1 shows example interrogation regions with increasing particle density.
Figure 1. Demonstration of the impact of increasing particle density on PIV images. Visual inspection shows the center image pair contains enough particles to identify the movement of particles from the first to second image (not true for the top image pair), while most particles remain distinct (which is not true for the bottom image pair).
As shown in Figure 1, PIV users should introduce enough particles into the flow field to achieve the desired particle number for each interrogation region, while ensuring there are not so many particles that the particle images are not distinct. Fortunately, typical PIV setups involve the manual introduction of particles to the flow, and users should slowly introduce particles until images show a good balance of these considerations. Empirical observations show that each interrogation region should have at least five particles.
Author: Jack Elliott
Date Published: June, 2022