Correlation Methods of PIV Analysis

Abstract

As described in the previous chapter, Particle Image Velocimetry (PIV) uses images of seeded marker particles in a fluid flow to measure two-dimensional or three-dimensional instantaneous velocity fields in experimental fluid mechanics. The seeded fluid flow is illuminated by short duration pulsed sheets of light at precise time intervals to obtain particle images that are recorded on a digital video camera array, on photographic film or on a hologram. The velocity vector field is obtained by analyzing these recorded images to measure the particle displacements and thus determine the velocity by knowing the time interval. Although many methods of PIV interrogation have been explored experimentally, as discussed by Adrian1, Buchhave2, Gray3 and Hinsch4, the broad range of methods can be reduced to a smaller group of alternative methods based upon the seeding density of particles within the flow field, denoted by C and defined to be the number of seeded particles per unit volume of the fluid. For a sufficiently high seeding density, the local velocity of the fluid in a small volume of the flow can be determined by measuring the particle image displacements within a corresponding digitized region of the image field, known as an interrogation spot.