Stereo-PIV measurements and Image Analysis

To accomplish the objectives of the task E6.IN1, using the INSEAN underwater probe, a Stereo-PIV measurement campaign has been performed to investigate the flow around the Alliance ship scale model. The experimental campaign has been carried out at the B600 towing tank of DGA that allowed to study a large, 1/10, scale model in order to reproduce as much as possible the fluid dynamic phenomena involved in the ship scale. Couples of two-frame images have been collected at 5 cross-flow planes, for 2 model velocities, in 2 model configurations - with and without appendages. A multi-plane calibration procedure has been used so to implement the Soloff technique [1] for a high reconstruction accuracy of the third velocity component. 3C-2D instantaneous velocity fields have been obtained with a standard iterative multi-pass window deformation algorithm applied to both two-frame images acquired with the two cameras. In order to increase the spatial resolution of the measurement, the so-called patching technique has been used; large areas have been subdivided into smaller regions using appropriate camera objectives and investigated separately with the use of a translation stage moving the whole acquisition probe. Once the instantaneous vector fields have been extracted, an ad hoc algorithm has been designed to evaluate all the quantities of interest over the original regions providing, for the actual case, a spatial resolution as high as 2.55 mm (vector grid width) . Statistical quantities have been evaluated for CFD code validation.