Analysis Based on Momentum Theory for Ceiling Wall Effect on Aerodynamic Characteristics of a Rotor

Abstract

Small-scale rotorcraft, such as multi-rotor UAVs, are widely used for various purposes. The industry is intensely interested in aerial vehicle inspections of infrastructures such as bridges or tunnels. During inspection activities, aerial vehicles must approach their walls. In those situations, walls affect the airflow around the rotor and the rotor’s aerodynamic characteristics. This study aims to understand and model the wall effect that appears when the rotor approaches the wall and to develop a compensation method for the wall effect. The ceiling wall effect is focused on in this paper. A horizontal air velocity is induced upstream due to air intake from the surrounding region if the rotor approaches the ceiling wall. This paper developed a model of the change in induced speed, thrust, and required power due to the ceiling wall effect based on momentum theory, considering the airflow in the direction parallel to the ceiling wall induced near and upstream of the rotor disk surface. The effectiveness of the proposed method is demonstrated by comparing the experimental results of the thrust ratio at constant power and the thrust ratio at constant power.