A Translating Wind Tunnel for Testing the Dynamic Response of Untethered Bodies to Transverse Gusts

The dispersal mechanisms of natural and engineered free-falling bodies are greatly affected by their response to wind gusts. In particular, understanding this response is critical for predicting their dynamics and resulting dispersal. Additionally, gusts can significantly impact the performance and survivability of low-inertia aerial vehicles during flight. Current methodologies fall short in studying untethered or free-falling models subjected to common gusts, especially transverse gusts. These gusts are characterised by a sudden, uniform change in flow velocity orthogonal to that previously experienced by the flyer. Existing methods are not applicable to such scenarios.

We introduce a unique vertical wind tunnel capable of imparting horizontal accelerations equivalent to those experienced during atmospheric transverse gusts. This wind tunnel translates horizontally in the direction normal to the flow with the same acceleration as the simulated gust. As a result, it generates the pressure gradient typical of a transverse gust without introducing a shear layer, as seen in Küssner’s model. The facility can replicate arbitrary gust profiles, including both discrete (e.g., Wagner’s gusts) and periodic (e.g., Theodorsen’s gusts).

The novelty of this approach lies in its ability to create arbitrarily strong, vorticity-free gusts. This enables detailed studies of how flyer inertia affects orientation, flight trajectory, and modifications to the surrounding flow field. Understanding flyer responses under these transverse gust conditions is crucial for designing control systems in small drones and micro-robots, as well as for predicting the dispersal patterns of passive flyers. Furthermore, to demonstrate the methodology and effectiveness of our approach, we present preliminary data on the dynamics of an untethered dandelion diaspore subjected to a discrete transverse gust within this translating wind tunnel.

For the first time, this facility enables investigation into coupled transverse gust-body interactions across a wide range of flyers and free-falling bodies, including micro- and nano-drones, unpowered micro-robots, plant seeds, debris, and more.