In trajectory planning and control design for unmanned air vehicles, highly simplified models are typically used to represent the vehicle dynamics and the operating environment. The goal of this work is to perform real-time, but realistic flight simulations and trajectory planning for quad-copters in low altitude (<500m) atmospheric conditions. The aerodynamic model for rotor performance is adapted from blade element momentum theory and validated against experimental data. Large-eddy simulations of the atmospheric boundary layer are used to accurately represent the operating environment of unmanned air vehicles. A reduced-order version of the atmospheric boundary layer data as well as the popular Dryden model are used to assess the impact of accuracy of the wind field model on the predicted vehicle performance and trajectory. The wind model, aerodynamics and control modules are integrated into a six-degree-of-freedom flight simulation environment with a fully nonlinear flight controller. Simulations are performed for two representative flight paths, namely, straight and circular paths. Results for different wind models are compared and the impact of simplifying assumptions in representing rotor aerodynamics is discussed. The simulation framework and codes are open-sourced for use by the community. Nomenclature Symbols c = Rotor chord, m c d = Lumped drag coefficient
Determination of the aeroacoustic emission from an axial fan in a non-anechoic environment is a challenging experimental task given ambient noise and acoustic reflections from surrounding objects. Successful strategies to address this task for a representative nine and three blade fan are presented. An array consisting of ten microphones was constructed and placed in the upstream region of the axial fans to measure the fan acoustic signature at ten distinct locations. A novel delay and sum (DS) beamforming technique (that allows precise time delays to be established by the use of cross correlation techniques) was applied to the microphone outputs in order to separate the fans' acoustic emissions from the ambient noise and reflections from the facility walls. A numerical simulation was developed to represent the experimental facility and the measurements. The numerical simulation indicated that the extraneous noise can be satisfactorily separated from the fan noise using the array measurements and post processing the acoustic data with the present DS beamforming technique.
The interaction of trailing vortices with lifting surfaces is investigated using two levels of modeling fidelity. A RANS-based computational fluid dynamics solver is considered as the high-fidelity computational model and a vortex panel method with a propeller model is considered as the low-fidelity computational model. The high-fidelity model is first validated against available experimental data obtained from the interaction of a trailing vortex generated by an upstream wing with a downstream wing. The ability of the models to represent the development of the vortex wake and integrated loads is assessed for a number of parametric configurations, including a case in which the vortex core directly impacts the wing surface. Following this, configurations of an isolated propeller and a wingmounted propeller are studied. In all of these cases, the high-fidelity model is effective in predicting the details of the flow and integrated airloads. The low-fidelity model, while less accurate is shown to successfully represent integrated quantities well at orders of magnitude less cost than the high-fidelity model, justifying its role as a viable tool in design and trajectory planning applications.
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