LEGO calibration targets for large-FOV particle image velocimetry

Particle image or particle-tracking velocimetry nonintrusively provides velocity field information, and the proposition large field-of-view (FOV) measurements are highly attractive from an experimental standpoint. Stitching multiple smaller FOVs to achieve the large FOV of interest is an approach that faces challenges rooted in the calibration process. For stereoscopic PIV (SPIV), the use of a multi-level target simplifies calibration. However, this is problematic for large-FOV measurements, as standardised multi-level targets are relatively small and expensive. LEGO((R)) bricks are well-suited to the construction of large, customised multi-level targets due to their high-dimensional tolerance and their stackability with high precision. To evaluate the feasibility of LEGO((R))-based targets, a two-sided multi-level target covering 380 x 1150 mm was created and used for SPIV measurements of the inflow conditions of the Atmospheric Wind Tunnel Munich. Calibrations were also performed using the Type 31 target for comparison. Analysis of the datasets with both calibration targets shows good agreement in the measurement of the streamwise, out-of-plane component u. A parametric study of different LEGO((R)) target configurations was used to verify the calibration performance of the targets as well as identify optimal configurations for experimental use. Due to the high level of agreement in calibration parameters and quantitative and qualitative flowfield parameters in PIV tests, as well as the consistency observed in the subsequent parametric study, LEGO-based calibration targets show potential for further development and usage in large-FOV measurements. [GRAPHICAL ABSTRACT]