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The emerging field of urban air mobility (UAM) offers a novel transportation method for civil, commercial, and military applications. Vertical take-off and landing (VTOL) configurations present challenges for performance prediction during crucial flight operations. An advanced computational framework for predicting propeller performance in electric vertical takeoff and landing (eVTOL) aircraft during transition flight is essential for future concept designs. This research extends the Blade Element Momentum Theory (BEMT) to model propeller behavior at high incidence angles, crucial for eVTOL operation.
The study begins with a review of tilt-wing/rotor configurations for eVTOLs and tackles the complex aerodynamic phenomena associated with rotors at incidence. An extended BEMT methodology is then developed, incorporating dynamic inflow modeling and semi-empirical corrections to account for the intricate flow field encountered during transition flight. This model is implemented in MATLAB, enabling efficient simulation across a wide range of operating conditions.
Validation of this computational propeller model was achieved through experimental testing that was conducted using both the low- and high-speed test sections of Old Dominion University's subsonic wind tunnel facility. Two different sizes of conventional, fixed pitch, APC manufactured off-the-shelf propellers were selected for testing and validation. The experimental design employed Design of Experiments (DOE) methodology, allowing for efficient exploration of the multidimensional parameter space of propeller operation.
The study also explored a simulation surrogate model using Gaussian Process Regression (GPR) to develop rapid prediction tools for propeller performance. A comprehensive comparison between experimental results and simulation predictions demonstrated good agreement for the two propellers, with RPM values from 4000 to 6000 and incidence angles from 0° to 80°. For the APC 11x7 propeller, average errors were approximately 5% for thrust and 10% for normal force and torque coefficients. The APC 13x6 propeller showed similar accuracy, with average errors of approximately 10% for thrust and 8% for normal force and torque coefficients. This work contributes to eVTOL propulsion research by providing a validated reduced-order computational framework for predicting propeller performance during critical transition flight regimes, offering valuable resources for future eVTOL propulsion system design and optimization.
