Identification of a new source of peak locking, analysis and its removal in conventional and super-resolution PIV techniques

One of the key factors that limit accuracy of particle image velocimetry (P IV) is the peak-locking effect. In this paper, a previously uncharacterised source of peak locking is presented. This source is neither related to the sensor geometry nor the subpixel resolution peak-fitting algorithms. It is present even when the particles are well described in terms of sensor spat ial resolution (i.e. for particle diameters larger than 2 pixels). If no sp ecific actions to avoid it are taken, its effect is especially important in those super-resolution systems that are based on iteratively reducing the size of the interrogation window. In this work, the mentioned source and it s effects are studied and modelled. Based on this study, the actions requir ed to avoid this type of peak locking are described. This includes the most usual correlation-based PIV systems, as well as super-resolution ones. Onc e this source of inaccuracy is avoided, it is possible to discriminate the performance of different types of correlation algorithms. As a consequence, specific proposals for the algorithms in the last steps of multigrid super -resolution PIV systems are given. The performances of the proposed solutio ns are verified using both synthetic and real PIV images.