Parametric study of aerodynamic performance of equivalent ducted/un-ducted rotors

Abstract

Abstract This paper presents the performance analysis and a parametric study of equivalent ducted/un-ducted rotors using high-fidelity CFD methods. A model-scale ducted rotor case by NASA was analysed and used as the initial design. An equivalent un-ducted rotor producing the same thrust and power was first derived using the momentum theory. The ducted/un-ducted configurations were later scaled to support a four-rotor vehicle of 6,000 kg using a BEMT model. High-fidelity CFD simulations of the scaled designs were then performed. Far-filed acoustics of the two configurations was also examined using the FW-H equations. Compared to the equivalent open rotor, the ducted rotor had a significantly reduced frontal area and was also able to deliver the desired thrust at lower torque and reduced noise, but the power was higher due to the higher RPM. A parametric study was then performed in hover and in forward flight to study the performance trends subject to variations of tip speed, blade pitch, blade radius, chord, twist, and duct thickness. Kriging surrogate models were constructed to provide an impression of the performance response to the particular design change. Both configurations showed similar responses to most design variables, but the sensitivity was different between configurations and between flight conditions. Detailed analyses of the parametric results are presented to guide ducted rotor designs.