Local field correction PIV: on the increase of accuracy of digital PIV systems

Cross-correlation Particle Image Velocimetry (PIV) has become a well known and widely used experimental technique. It has been already documented that difficulties arise resolving velocity structures smaller than the interrog ation window. This is caused by signal averaging over this window. A new cr oss-correlation PIV method that eliminates this restriction is presented. T he new method brings some other enhancements, such as the ability to deal w ith large velocity gradients, seeding density inhomogeneities, and high dis persion in the brightness of the particles. The final result is a method wi th a remarkable capability for accurately resolving small scale structures in the flow, down to a few times the mean distance between particles. When compared to particle tracking velocimetry, the new method is capable of obt aining measurements at high seeding density concentrations. Therefore, bett er overall performance is obtained, especially with the limited resolutions of video CCDs. In this paper, the new method is described and its performa nce is evaluated and compared to traditional PIV systems using synthetic im ages. Application to real PIV data are included and the results discussed.