Characterization of fluid flow inside a multi-fan-array wind tunnel for insects

How flying insects, like fruit flies, navigate turbulent environments in their day to day lives continues to be an active area of interest. To study their behavior in a controlled environment, we have developed a multi-fan-array wind tunnel with a 90x45x45cm^3 working test section. The fan array consists of 36 80mm fans configured in a 6x6 grid, with each fan being independently controlled to provide wind speeds between 0 and 100 cm/s. The fans can be operated in several different configurations designed to produce laminar, shear, and turbulent flow. To characterize the fluid flow in each of these conditions, we used a hot wire anemometer to measure wind speed and turbulence intensity at the front middle and back sections. With the incorporation of flow manipulators our wind tunnel can achieve laminar flow with a turbulence intensity of just 1.1%, approximately .1% larger than an industrially built wind tunnel at the same wind speed. Utilizing a splitter plate we can generate a significant distinction between a laminar region and turbulent region inside the wind tunnel. Finally, we can induce turbulence in the entirety of the wind tunnel with either a static fan array pattern or a dynamically shifting fan pattern. Through analyzing the power spectral density of the time trace for each turbulence set up, we found that the static configuration, in which the fans are set to be on and off in a checkered pattern, has a -5/3 slope indicating turbulence in the frequency range of 10 to 100 hz while the dynamic setup has a turbulence range around 1 to 100 hz. Our fan-array design provides a convenient test-bed for studying how insects navigate both laminar and turbulent environments, with a particular future interest in how turbulence impacts odor plume tracking behavior.