Aerodynamics Optimization of a Ducted Coaxial Rotor in Forward Flight Using Orthogonal Test Design

Abstract

To investigate the aerodynamic complexities involved in the combination of freestream and propeller’s suction flow field of ducted coaxial rotors system in forward flight, an orthogonal L16(43) test design has been applied to optimize the design parameters including forward speed, pitch angle, and axial spacing between rotors. Multiblock grids and Multiple Frame of Reference (MFR) method are adopted for calculating aerodynamic performance of the system, hover characteristic was compared with experimental data obtained from the test stand, and the thrust performance is well predicted for various rotor spacing and a range of rpm. This solution approach is developed for the analytical prediction of forward flight and the simulation results indicated that the design parameters influenced lift, drag, and torque reduced in the order: wind speed > rotor spacing > pitch angle, wind speed > pitch angle, and rotor spacing > wind speed > pitch angle, respectively. The optimal rotor spacing and pitch angle were determined to maximize the aerodynamic performance considering high lift, low drag, and trimmed torque.

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“…Research on the ducted fan has been actively implemented from the early 2000s until recently, and the studies were mainly focused on a single ducted fan for a small UAV (unmanned aerial vehicle) that requires VTOL (vertical take-off and landing) ability in the 2000s [1][2][3]. After the 2010s, as VTOL vehicles of various concepts including small UAVs were introduced, various forms of ducted fans appeared naturally such as fan-in-wing [4][5][6], multiduct [7], and coaxial [8,9] types. In addition, studies have been conducted on the performance of ducted fans in various ways.…”