Generating controlled gusts using vortex rings

The control and stability of flying and swimming animals is typically determined by measuring their responses to discrete gust perturbations. For the rigorous measurement and analysis of such responses, it is necessary to generate gusts that are precise, controllable and repeatable. Here, we present a method to generate discrete gusts under laboratory conditions using a vortex ring. Unlike other methods of gust generation, the vortex ring can be well characterized and is highly controllable. We first outline the theoretical basis for the design of a gust generator, and then describe an apparatus that we developed to generate discrete gusts. As a case study, we tested the efficacy of this method on freely-flying soldier flies Hermetia illucens. The method described here can be used to study diverse phenomena ranging from natural flight and swimming in insects, birds, bats and fishes, to the artificial flight of drones and micro-aerial vehicles.