Underwater SPIV probe for towing tank applications

A unique, highly modular and flexible underwater system for stereoscopic particle image velocimetry (PIV) measurements is presented. The instrument is intended for planar three-dimensional velocity measurements in large facilities such as towing tanks and tunnels. A novel stereo-PIV calibration technique is adopted for the probe. The central feature of the proposed technique is that the calibration of the stereoscopic system is based upon the measurement of a calibrated flow. This is achieved through a first two-dimensional calibration of the measurement plane using a single target point, followed by a perspective and laser sheet thickness optimization that makes use of the measurement of a known flow, e.g. a uniform flow. This technique results in three-dimensional measurements of enhanced accuracy with a simpler calibration phase, which compensates for the mechanical misalignment and eliminates the errors deriving from the classical target dot identification. The technique is particularly well suited for towing tanks and other large facilities. Finally the flow survey around an underwater vehicle by SPIV is presented. In such experiment large measurement area and high spatial resolution, required for CFD validation, need to be achieved simultaneously