Instantaneous self-calibration of a 3D imaging system in industrial facility with strong vibrations

Abstract

The flow on the suction side of a half-wing model is investigated by means of 3D Lagrangian particle tracking (LPT) with Multi-Pulse Shake-The-Box and stereoscopic particle image velocimetry. The experiment is carried out in the Low Speed Wind-Tunnel facility (LSWT) at the Airbus UK site (Filton, England). Illumination is provided by a multi-pulse system consisting of two dual-pulse lasers. A 3D imaging system is composed of five double-frame cameras; a two-camera subset can be employed in stereoscopic fashion. Due to the constrains posed by the limited optical access to the measurement region, three cameras are installed inside the wind-tunnel test section. As a consequence, significant vibrations occur during the operation of the wind-tunnel, leading to large unsteady decalibration of the imaging system (up to 120 px). A tailored single-snapshot self-calibration approach is proposed here which makes use of standard volume self-calibration and particle triangulation from the 3D imaging system to detect and correct the camera decalibration for each instantaneous recording. Results shows that the disparity error can be reduced to less than 0:1 px, a suitable value for both accurate 3D particle triangulation using the full imaging system and for stereoscopic evaluation of the out-of-plane velocity component with PIV making use of a two-camera subset.