Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 65, Number 13
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session W02: Aerodynamics: Control (10:00am - 10:45am CST)Interactive On Demand
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W02.00001: Experimental gust mitigation using model based feedforward and feedback control Benjamin Herrmann, Johannes Pohl, Steven L. Brunton, Richard Semaan Wing-gust encounters arising from flight over complex terrain or adverse weather are unavoidable and cause large lift transients that may result in structural damage due to extreme loads and/or fatigue. With the potential to extend the lifetime and improve the safety of air vehicles, gust mitigation through control is challenged by sensor noise, time-delays, and short response-time requirements. In this study, we build and deploy a closed-loop controller on an airfoil equipped with an actuated trailing-edge flap in a wind tunnel experiment. The control objective is the regulation of the lift coefficient, measured in real-time along the mid-section using fast-response pressure sensors. The onset and magnitude of gust disturbances, which are generated upstream by a pitching airfoil, are fed through using a two-component cross-wire located upstream of the leading edge. Feedback and feedforward controllers are designed based on reduced-order models for the lift response to flap actuation and perturbations in the cross-wire signals identified from open-loop experiments. The combined control setup proves to be an effective strategy for lift regulation during gust encounters, rejecting disturbances, attenuating noise, and compensating for model uncertainty. [Preview Abstract] |
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W02.00002: Feedback control of the unsteady loading on a high-rise building Xiao Hu, Aimee Morgans With the frequency of significant weather events increasing, it is critical to predict and mitigate the response of high-rise buildings to wind loading. In this work, turbulent wakes arising from air flow around a benchmark high-rise building -- the Commonwealth Advisory Aeronautical Council (CAARC) building -- are numerically investigated using Large Eddy Simulation (LES). Such buildings protrude into the atmospheric boundary layer. In this work, the synthetic eddy method is employed to simulate the oncoming air flow. The mean and unsteady forces and moments on the building are compared to available experimental results. The coherent flow structures are then analyzed with a view to informing the choice of sensors and actuators for feedback control. To attenuate the unsteady loading, actuation in the form of unsteady synthetic jets along edges of the building is implemented. The sensor for feedback control is the unsteady pressure force on the back face of the building. Harmonic open-loop forcing across different frequencies and amplitudes is used to characterize the unsteady loading response to actuation, via fitting of a linear model. This model will be used to develop a linear feedback controller for reducing the unsteady loading, and its performance in simulations assessed. [Preview Abstract] |
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W02.00003: Reinforcement Learning for Flow-Informed Flight Control Peter Renn, Morteza Gharib While flying in real-world environments, unmanned aerial systems (UAS) often encounter significant fluid disturbances that challenge the capabilities of conventional sensing and control methods. Current disturbance rejection strategies do not consider fluid interactions, instead sensing and correcting only for the resulting inertial changes. On-board flow sensing allows UAS to characterize interactions with the fluid environment, potentially enabling superior control in turbulent conditions. Sufficient characterization of the state of the surrounding flow may allow for predictive control strategies through which UAS react to fluid disturbances before inertial effects can be sensed. In this presentation, we explore the use of reinforcement learning (RL) for identifying and applying effective ``fluid-aware'' control policies in an experimental setting. A symmetric airfoil is fitted with flow sensors to model a fixed-wing UAS, and a state-of-the-art fan array wind tunnel is used to simulate realistic flow conditions for training. By developing RL strategies for ``fluid-aware'' flight control via simplified experimental models, we aim to help develop a new generation of UAS capable of superior flying in adverse flow conditions. [Preview Abstract] |
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W02.00004: Transitory, Bi-directional Control of Wing Aerodynamics using Trailing Edge Fluidic Actuation Yuehan Tan, Ari Glezer, Ryan Patterson, Peretz Friedmann Bi-directional control of the aerodynamic loads on a wing at low-to moderate angles of attack using fluidic actuation is explored in a joint experimental/numerical investigation. Transitory actuation is effected by a bi-stable fluidically-switched actuation jet upstream of the trailing edge (0.88c) on each of the suction and pressure surfaces. The interactions of the jets with the embedding cross flow following the onset and termination of the actuation are investigated using time-resolved measurements of the aerodynamic loads and the unsteady velocity field using particle image velocimetry (PIV). It is shown that coupled pulsed actuation on the pressure and suction surfaces leads to rapid (within 7Tconv) bi-directional changes in lift ($\Delta $CL up to $+$0.52/-0.41) along with some reduction in drag. Phase-locked velocity measurements and complementary CFD simulations near the trailing edge demonstrate the temporal alteration of the balance between cross-stream transport of vorticity concentrations and of vorticity flux into the near wake. [Preview Abstract] |
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