A speckle projection-based 3D digital image correlation method for measuring dynamic liquid surfaces

Measuring dynamic liquid surfaces is a significant challenge in fluid mechanics and sloshing dynamics, with a notable lack of high-precision, effective full-field measurement methods. To resolve this challenge, this research proposes a speckle projection-based 3D digital image correlation (3D-DIC) method for the measurement of dynamic liquid surfaces. The approach employs liquid staining and speckle projecting to create textured patterns on the liquid surface, which are then captured by binocular cameras. The binocular cameras are calibrated using a ratio-invariant method to accurately obtain the internal and external parameter matrices. Subsequently, algorithm based on zero-mean normalized cross-correlation (ZNCC) is utilized to reconstruct the dynamic liquid surface wave height field. To validate the accuracy of the method, a geometric optical numerical model is established to simulate binocular images of regular wave liquid surfaces with projected speckle patterns. The results show that full-field root mean square (RMS) error in simulated liquid surface measurement is less than 0.019 mm. Physical experiments were further conducted to confirm the method's applicability, achieving a maximal measurement error of 0.133 mm for real dynamic liquid surfaces. Results demonstrate that the proposed method achieves high-precision, non-contact, and full-field measurements of dynamic liquid surfaces, making it ideal for laboratory measurements of flowing liquids.