PIV velocity refinement using optical flow for high resolution flow measurement: Development and preliminary validations

In this study, we propose a method to enhance the particle image velocimetry (PIV) velocity resolution by using global optical flow along with image warping. A global optical flow formula proposed by Brox et al. [18] is adopted to compensate the intensity changes of PIV image pairs, which depend on the set-up and synchronization of a laser and a camera. The proposed method is quantitatively evaluated and validated using synthetic particle image pairs generated for Rankine vortices and reference DNS-based velocity data. It turns out that the proposed method outperforms the conventional PIV method in capturing turbulent structures due to its enhanced spatial resolution. Finally, the proposed method is applied to the real PIV particle images. Experiments were conducted on the vortex and multiple rectangular jet flows. The results show that the proposed method successfully improves the velocity resolution while preserving the conventional PIV results, as well as works out quantitative hydrodynamic characteristics. The method presented in this paper will be leveraged to generate high fidelity experimental data for validation of computational fluid dynamics (CFD) codes.