Abstract
This study examines the mechanism of thrust increase due to the ceiling effect in near-ceiling flight, which is one of the concerns for the practical application of micro air vehicles in indoor environments. We also proposed a novel rotor blade shape with a pressure recovery hole as one of the passive control techniques and investigated its effectiveness in controlling the thrust increase. The obtained results showed a rapid thrust increase, with an outward swirling flow between the rotor blade and ceiling, observed with a rectangular blade with an extremely small distance between the upper surface of the rotor blade and ceiling. The rapid thrust increase was caused by a pressure difference between the rotor blade and the lower surface of the ceiling in addition to the rotor blade rotation, which generated an outward swirling flow between the rotor blade and ceiling. In addition to the force generated by the pressure difference between the upper and lower blade surfaces due to their rotation, the negative pressure area created by the rotor blades reversed the airflow. For the invented rotor blade, the ratio of the pressure recovery hole to the rotor blade radius was 0.5, which maintained approximately 90% or more of the thrust without the upper wall of the rectangular blade; moreover, the distance between the ceiling and the rotor blade at which the thrust began to increase rapidly became shorter, flight performance was generally maintained in the absence of the ceiling, and the thrust increase amplitude was suppressed.
