A towing-flume with motion-tracking optical flow diagnostics.

Flows around objects undergoing unsteady motion are ubiquitous in both nature and engineering. However, the complexity of such objects' motions often constrains the reproduction of realistic unsteady flow scenarios and hinders the application of field-wide optical measurements within the confines of a laboratory. This study introduces a towing-flume facility equipped with a co-moving optical measurement system capable of speeds up to 1 m/s. In addition, a free stream can be generated using an integrated axial pump. The object's unsteady motions with multiple degrees of freedom are achieved via a carriage system integrated with mounted linear translation stages and goniometers. The optical setup comprises co-moving imaging and illumination systems, both of which traverse the exterior of the flume in synchronization with the main carriage under the control of a host computer. Validation tests and demonstration experiments confirm the high-fidelity reproduction of complex unsteady motions, precise synchronization with a speed error of less than 1%, and high-resolution imaging capabilities. These features enable both qualitative and quantitative investigations into fundamental and applied engineering problems.