Wing Design and Optimization for a Flapping Wing Micro Air Vehicle

The shrouded rotor concept has been gaining popularity in VTOL micro air vehicle (MAV) designs. It is well known that the static thrust performance of a propeller can be significantly improved by enclosing it in a shroud or duct. However, there is a lack of detailed information available to the MAV designer on the effects of different design variables, like diffuser divergence angle, inlet lip radius and blade tip clearance, on the performance of shrouded rotors at the low Reynolds numbers (∼20,000 - 30,000) corresponding to MAV applications. An investigation of the effects of such variables was conducted on four different rotor-shroud combinations, using three shrouds with different diffuser included angles (0°, 10° and 20°) and inlet lip radii (6%, 9% and 13% of rotor diameter). The experiments show that increasing the lip radius and providing a smooth fairing for the rotor after-body may help increase the thrust produced, and that decreasing the blade tip clearance may enable reductions in power consumption. A novel method for incorporating the expansion ratio of the shroud’s diffuser into a blade-element-momentum theory analysis of a shrouded rotor is proposed, which shows good agreement with experimental data.