PIV operation in hydrodynamic facilities, a flat plate benchmark test comparing PIV systems at different facilities

As part of the European Network of Excellence Hydro Testing Alliance (HTA) one research activity named as JRP1 has been defined to investigate and develop new and improved methods for PIV operation in hydrodynamic facilities. The group has been working on a review of potential applications and needs from hydrodynamic facilities, then selecting targeted applications for development of solutions (especially reviewing needed adaptations on experimental set up), and ultimately conducting tests in facilities. In particular, a benchmarking program has been established by considering the wake flow of a piercing surface flat plate at incidence.. The objective was to realize a benchmark program to evaluate the performance of the SPIV (Stereo PIV) systems to be used among the JRP-1 partners with the main requirements being a simple and cheap experimental setup that would be representative of typical SPIV problems in commercial hydrodynamic facilities such as towing tanks and cavitation tunnels. Analysis and comparisons of the mean flow fields between three different institutions revealed that the PIV technique is fairly robust and reliable under ideal measurement conditions. One significant outcome from the comparisons is the weakness of the technique with respect to surface light reflections. Reduced laser energy and larger particle could help in increasing the image Signal to Noise Ratio. However when the scattering angle from the model surface is matching one of the camera angle view there is no way to overcome the problem and a measurement is not possible. In such case special model preparation techniques such as a Perspex insert is required to overcome the problem. Despite the fact that the same model was used in three different facilities, there were some differences in the flow field, primarily with respect to the location of various flow features. Whether this is a result of different flow fields being obtained, or a result of how the data is interpolated onto a specified measurement grid is difficult to conclude.