Numerical and experimental study on the addition of surface roughness to micro-propellers

Micro aerial vehicles are making a large impact in applications such as search-and-rescue, package delivery, and recreation. Unfortunately, these diminutive drones are currently constrained to carrying small payloads, in large part because they use propellers optimized for larger aircraft and inviscid flow regimes. Fully realizing the potential of emerging microflyers requires next-generation propellers that are specifically designed for low Reynolds number conditions and that include new features advantageous in highly viscous flows. One aspect that has received limited attention in the literature is the addition of roughness to propeller blades as a method of reducing drag and increasing thrust. To investigate this possibility, we used direct numerical simulation to conduct a numerical investigation of smooth and rough propellers. Our results indicate that roughness produces a 2% increase in thrust and a 5% decrease in power relative to a baseline smooth propeller operating at the same Reynolds number of Re-c = 6500, held constant by rotational speed. We complement our numerical findings using thrust-stand-based experiments of 3D-printed propellers identical to those of the numerical simulations. Our study indicates that surface roughness is an additional parameter within the design space for micro-propellers, which may offer improved drone efficiencies and payloads.