Investigation of Shadow Effects in Reflective Ultrasonic Anemometers Based on Particle Image Velocimetry and Computational Fluid Dynamics

To address the measurement instability of reflective ultrasonic anemometers in complex wind fields, this study systematically investigates the mechanisms by which shadow effects caused by transducers and reflector support pillars affect measurement accuracy under varying wind speeds and directions. By integrating particle image velocimetry (PIV) experiments with computational fluid dynamics (CFD) simulations, 1:1 and 1:2 scale models are employed to reveal the flow field characteristics and error mechanisms. The results indicate that at a wind direction of 0°, wall-following vortices and turbulent wakes generated by transducer structures cause systematic wind speed deviations along the measurement paths. At a 45° wind direction, flow disturbances around the support pillars become the dominant source of shadow effects. The 1:1 scale model exhibits insufficient decay of large-scale, low-frequency turbulent energy, resulting in the accumulation of turbulent kinetic energy and significant wind speed errors at 0°. In contrast, the 1:2 scale model enables efficient energy transfer through high-frequency, small-scale vortices, enhances vortex intensity uniformity, and achieves improved spatial homogeneity in cross-wind measurement errors. These findings provide an important theoretical foundation for improving the high-precision measurement performance of reflective ultrasonic anemometers in complex wind environments.