EXPERIMENTAL INVESTIGATION OF THE FLOW AND ACOUSTIC CHARACTERISTICS OF A DUCTED PROPELLER WITH INCOMING FLOW

In urban air mobility applications, shrouding the propeller can significantly improve its aerodynamic efficiency and enhance the vehicle’s operational safety. The increased aerodynamic efficiency can be linked to the flow features around the propeller and its wake. In this study, we evaluate the flow characteristics of a ducted propeller under hover conditions and different axial flow speeds in an anechoic wind tunnel using particle image velocimetry, focusing on propeller wake development. The clearance between the propeller and the duct is also varied, and off-center variations are studied, which introduce an asymmetric behavior to the flow and the aerodynamic loads. The changes in the thrust generated by the propeller and the duct are measured, and the far-field noise is measured at different observer angles with an arc microphone array. The results show that increasing the axial flow speed reduces the thrust generated by the propeller and the duct, but the flow can remain attached to the duct wall downstream of the propeller. A higher flow speed can also reduce tonal and broadband noise, which can be linked to a reduction in the blade’s steady loading and turbulent kinetic energy, respectively. A larger tip clearance and off-centering between the propeller and the duct only produce limited changes in the thrust generation, but the size of the wake is reduced.