1. Low turbulence free surface water tunnel
Our self-design and constructed free-surface water tunnel features an elongated test section with dimensions of 8 m x 0.5 m × 0.5 m. The maximum bulk velocity is 1.5 m/s, and the turbulent intensity is below 1.6% [1]. The combination of the elongated test section and high maximum velocity enables the generation of turbulent flows across a wide range of Reynolds and Froude numbers, including turbulent boundary layers with a Reynolds number based on wall shear stress greater than 7,000.
The video below shows air-bubble entrainment through free-surface ventilation in the wake of a surface-piercing triangular wedge in a flow of 1.2 m/s (Fr=1.8).
[1]. Butler, D., Dar, S., Nguyen, M., Eluchi, C., Zhou, K., Wang, C. (2025). "Design of a high-speed, low-turbulence water flume with initial application to free surface turbulent wake flow." Theoretical and Applied Mechanics Letters, 100621.
2. Defocusing particle image velocimetry (DDPIV)
Although two-dimensional Particle Image Velocimetry (2D-PIV) has been successfully employed to measure unsteady flows across a wide range of scales, it only offers limited insights of the naturally three-dimensional turbulent flows. Time-resolved volumetric flow diagnosis capability is highly desired in unsteady and turbulent flow measurement and modeling. Defoucsing PIV (alternatively DDPIV) [1] offers a quick solution of resolving turbulent motions with high flexibility in the measurement volume size. In our laboratory, we recreated a DDPIV system through synchronizing 3 high-speed cameras (IDT Xtream Mini 3520, max resolution: 2560 x 1440 pixels, max frame rate: 2350 frame per second) to diagnose free-surface turbulent flows.
[1] Willert, C. E., & Gharib, M. (1992). Three-dimensional particle imaging with a single camera. Experiments in Fluids, 12, 353-358.
[2].Wang, C., Eluchie, C., Jeon, D., Gharib, M. “Measurement of turbulent wake flows near an unsteady free surface using defocusing PIV”, International Symposium of Particle Image Velocimetry 2025, Tokyo, Japan, 2025
3. Synchronized Multi-phane PIV
Turbulent wake flows of a surface piercing body exhibit strong an-isotropy in its dynamic characters. Through the employment of colored illumination light (e.g., blue and green laser) with suitable filters, we simulatenously resolve the spatio-temporal characters of turbulent wake flows near-to and far-way from the unsteady free surfaces.
4. Time-resolved stero-PIV
To better understand the dynamic instabilities of turbulent free-surface wake flow, we implemented time-resolved stero-PIV to characterise the streamwise coherent structures in the vicinity of unsteady free surfaces. Through the employment of 45 - degree water-filled prism, and a Scheimflug angle of XXX
5. High-magnification near-wall PIV
2D-PIV faces challenges in special measurement situations, such as in resolving the think viscous sub-layers of wall-bounded turbulent flows, due to its low spatial resolution limited by the finite size of interrogation window. The recently developed high-magnification near-wall PIV [2], through the combination of high-power continuous laser, specially designed optical lenses, and multi-frame PIV algorithm, can time-resolve the unsteady viscous sub-layers in high-Re turbulent boundary layers. This technique is adapted together with DDPIV to evaluate the drag reduction effect of our turbulence manipulation system and uncover the mechanisms behind the drag reducing flow structures.
[2] Willert, C. E. (2015). High-speed particle image velocimetry for the efficient measurement of turbulence statistics. Experiments in fluids, 56, 1-17.
4. Wave Basin and Towing Tank
Our lab also has access to state-of-the-art ship hydrodynamic research facilities operated by IIHR—Hydroscience and Engineering.