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View Video Presentation: https://doi.org/10.2514/6.2022-3218.vid The ability to accurately and rapidly assess unsteady interactional aerodynamics is a shortcoming and bottleneck in the design of various next-generation aerospace systems: from electric vertical takeoff and landing (eVTOL) aircraft to airborne wind energy (AWE) and wind farms. In this study, we present a meshless CFD framework based on the reformulated vortex particle method (rVPM) for the analysis of complex interactional aerodynamics. The rVPM is a large eddy simulation (LES) solving the Navier-Stokes equations in their vorticity form. It uses a meshless Lagrangian scheme, which not only avoids the hurdles of mesh generation, but it also conserves the vortical structure of wakes over long distances with minimal numerical dissipation, while being 100x faster than conventional mesh-based LES. Wings and rotating blades are introduced in the computational domain through actuator line and actuator surface models. Simulations are coupled with an aeroacoustics solver to predict tonal and broadband noise radiated by rotors. The framework, called FLOWUnsteady, is hereby released as an open-source code and extensively validated. Validation studies published in previous work by the authors are summarized, showcasing rotors across operating conditions with a rotor in hover, propellers, a wind turbine, and two side-by-side rotors in hover. Validation of rotor-wing interactions is presented simulating a tailplane with tip-mounted propellers and a blown wing with propellers mounted mid-span. The capabilities of the framework are showcased through the simulation of a tiltwing eVTOL vehicle and an AWE wind-harvesting aircraft, featuring rotors with variable RPM, variable pitch, tilting of wings and rotors, non-trivial flight paths, and complex aerodynamic interactions.
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Nonlinear, Low-Energy-Actuator-Prioritizing Control Allocation for Winged eVTOL UAVs
Winged eVTOL aircraft’s ability to generate aerodynamic lift with wings and to create upward thrust with upward-facing rotors makes these vehicles capable of the kind of versatile flight needed in urban environments. Because of these vehicles’ aerodynamic complexities and their unique methods of producing thrusts and torques, control allocation is needed to determine how to distribute force and torque efforts across the aircraft’s actuators. However, current control allocation methods fail to properly represent the actuators’ complex dynamics and are unable to harness the full potential of these over-actuated vehicles. Current shortcomings include modeling rotors as linear effectors while the wide range of airspeeds experienced by eVTOL aircraft leads to significant nonlinearities in the thrust and torque achieved by each rotor. This means linear control allocation methods may consistently fail to produce desired thrusts and torques, which can inhibit the vehicle from tracking a trajectory at best, and at worst can cause the vehicle to stall and lose control. Additionally, current control allocation methods are often unable to prioritize low-energy actuators resulting in shorter battery life. We present a nonlinear control allocation method that considers a nonlinear rotor model, allows for prioritization of low-energy control surfaces over rotors, and reliably accounts for actuator saturation. Simulation results show a 90% reduction in high-airspeed trajectory tracking position error from a typical, linear least-squares pseudoinverse control allocation method while maintaining comparable energy use.
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- Award ID(s):
- 1650547
- PAR ID:
- 10354828
- Date Published:
- Journal Name:
- Nonlinear, Low-Energy-Actuator-Prioritizing Control Allocation for Winged eVTOL UAVs
- Page Range / eLocation ID:
- 1 to 6
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1109/IETC54973.2022.9796842
