StereoPIV measurements on a Flat Plate Wake

Network of Excellence to facilitate the continuation of leadership of the European Hydrodynamic testing facilities. The objective of this alliance is to develop a formal and lasting structure to coordinate the definition and introduction of novel measurement, observation and analysis technologies for hydrodynamic model testing. This benchmark was defined to compare the efficiency of the Stereo PIV systems of the HTA Members and to compare their know-how. A Stereo PIV study on a flat plate wake is presented. The main aim of the present work is the efficiency testing of a Stereo PIV system. In fact the study of a flat plate wake, semi-submerged, near the free surface is a good benchmark for SPIV techniques. To achieve this work a flat plate (80 cm height and 50 cm chord) is vertically submerged to a depth of 30 cm; so the tip is near the free surface and is possible to test the acquisition system in presence of bubbles and other disturbances. Many tests are performed at varying incidence (5, 20 and 40 degrees) and velocity in a towing tank. The used Stereo PIV system is a fully submersible probe (Pereira et al. 2003); it is equipped with two 2048x2048 px2 CCD cameras and a 200 mJ Nd-YAG laser. The system is modular and can be assembled into different configurations. Hollow glass spheres of 30 mm diameter are used as seeding. The investigation zone is about 250 mm x 300 mm, the laser thickness is about 5 mm. The used target for the Soloff et Al.(1997)'s based calibration is a two-dimensional dotted grid, with a centre mark; grid spacing is 20 mm x 20 mm. Instead a pin target and uniform flow acquisitions are used for the flow-based calibration. The measurements give information on instabilities of the tip vortex of the plate. In fact the tip structures varying intensities and geometry with the Reynolds number and with the incidence the test comprises also measurement planes along the chord at defined distances from the leading edge