Three-dimensional flow visualization of hawkmoth wakes in unsteady flow

Recent work focuses on how unsteady aerodynamics are affected by unsteady flow. Flapping insects use unsteady flight mechanisms to navigate naturally unsteady environments. Capturing flight aerodynamics at the scale of flapping insects requires high spatial and temporal resolution. High wingbeat frequencies suggest aerodynamics may change on a millisecond timescale and wingspan is on the order of centimeters. In each wingstroke, vortices are produced along the wings and shed into the wake. These 3D flight mechanisms require 3D flow visualization with a behaving animal. We performed 3D particle tracking velocimetry (3D-PTV) on freely flying and tethered hawkmoths downstream of a 3D-printed flower. Within wingbeat time resolution was obtained with a 60mJ/pulse Nd:YLF laser operating at 1kHz. High spatial resolution was achieved in the 90mm x 50 mm x 20mm illuminated volume using micron-sized particles. The flower sheds vortices every 0.2-0.5s, but velocity in the downwash of the moth is the same as in steady flow. In free flight, the downwash is angled more below the animal than during tethered flight. Future work will quantify how flow around the wings changes in unsteady flow.