PAIRS: a free software application for robust and accurate digital particle image velocimetry

This contribution presents PAIRS (PArticle Image Reconstruction Software), a free software application designed to perform digital particle image velocimetry (PIV). PIV has become a standard tool in the fluid dynamics community for the analysis of turbulent flows. PAIRS, developed since 2000, includes several modules that allow to process also stereoscopic and tomographic PIV measurements. The current free release aims mainly at introducing the user to the module that handles the processing of double-frame or time-resolved 2D planar PIV images. PAIRS employs an iterative multi-grid approach based on image deformation. The user is allowed to select different types of process parameters in such a way to find the best compromise between accuracy and computational speed. Beyond this flexibility, preset strategies are also available for image analysis and designed for specific tasks like fast visualization of results in preliminary measurements or high accuracy in the final phase of investigation. PAIRS has been validated both numerically and experimentally and its accuracy and robustness have been proved during the 2nd and 3rd International PIV Challenges. PAIRS is based on a C library and relies on a user interface in Python to facilitate its usage and promote the diffusion.