Comparison of Multi-Fidelity Rotor Analysis Tools for Transitional and Low Speed Flight Regimes

Abstract

Urban and regional air mobility is a new mode of transportation currently attracting a lot of attention. Much effort is being put into preliminary design studies for various electric vertical takeoff and landing (eVTOL) concepts. Especially the aerodynamic modeling poses major challenges to both applications, the preliminary design and the control design of eVTOLs. One main factor affecting aerodynamic complexity is rotor aerodynamics and the respective couplings with other rotors, wings, and airframe. Thus, both applications share the need for a fast and user-friendly, yet sufficiently accurate analysis tool. This study provides an overview of four different rotor aerodynamic tools suitable for the preliminary and control design task of eVTOLs and a respective tool-selection for different applications. A cross-method comparison is performed for the tools DUST, FLOWLab, SARF and OpenVSP/VSPAero, with a focus on capturing complex rotor, rotor-rotor and rotor-wing aerodynamics. The Caradonna-Tung rotor, for which experimental data is available, represents the benchmark case. Subsequently, the Airbus A3 Vahana is used to extend the analysis to an aerodynamically complex eVTOL configuration for which a main wing rotor is analyzed. There, the rotor aerodynamics is analyzed in different flight phases, i.e., different phases of the transition. The comparison of the two cases shows possibilities and limitations with respect to the quality of the computational results and handling aspects of the respective tools. The results suggest that DUST provides accurate results and covers most relevant effects at the cost of higher computational complexity. Both, the FLOWLab tools as well as SARF provide sufficiently accurate results in a short time. Though, SARF does not cover friction drag and thus underestimates the rotor torque. OpenVSP often shows convergence issues, but otherwise shows comparable results to the previous two tools.