Harvard Microrobotics Laboratory

Vertical wind tunnels enable controlled studies of gliding, flapping, maneuvering, and stability in both biological insects and microrobots, where aerodynamic forces are small and flows are typically laminar. Existing tunnels are often large, expensive, and tuned for higher Reynolds numbers, making them ill-suited to micro-scale regimes (Re < 2300). Our objective was to create a compact, low-cost, open-source vertical wind tunnel that reliably delivers uniform, low-turbulence flow within micro-scale Reynolds numbers.

The mechanical design utilized Fusion 360 Computer Aided Design and was fabricated as a modular FDM 3D-printed system. Our flow conditioning stack includes two contraction nozzles to minimize wall/tip effects, two honeycomb stages (64mm and 40mm tall), and four 34-mesh screens at tuned axial positions to suppress large-scale turbulence and equalize velocity profile. The drive system features a 335 KV brushless motor with 8×6 three-blade propeller, controlled via ESC with Arduino-based PID loop using an FS3000 air-velocity sensor for closed velocity feedback.

Computer vision analysis was performed using Python, OpenCV, and OpenPIV to analyze wind particle flow and assess spatial uniformity. Particle Image Velocimetry (PIV) on laser-illuminated, glycerol-seeded images quantified velocity fields around test cylinders. Our results demonstrated steady laminar flow with classic laminar separated wake characteristics: uniform upstream flow, smooth diversion around cylinders, steady mirror-symmetric recirculation bubbles, no vortex shedding, and clean flow reattachment. The system provides precision control with closed-loop velocity regulation and ±0.02 m/s setpoint resolution across the full operational range.