This paper presents a new model-free control approach applied to a dynamical fluidic system. The main objective is to evaluate the ability of this closed-loop control technique to control the bistability of a turbulent wake flow past to a square-back Ahmed body. This bistable behavior occurs for some configurations depending mainly on the ground clearance. Due to the unsteady position of the wake vortex cores, the bistable phenomenon is responsible of a strong variation of the lateral force (drift force) and of a slight drag increase. Consequently, mitigating the wake symmetry-breaking modes can induce a substantial drag reduction. The feedback controller controls the drift using its ultralocal approximation and the estimation of its dynamics. The control signal is then applied to lateral blower actuators to suppress the spanwise bistability. The drift force is used as feedback to sense the wake flow, and concomitant velocity, forces, and pressure measurements are performed at a nominal Reynolds number of Reh = 2.86 × 105 to quantify and demonstrate the effectiveness of the present closed-loop control. Results show that for various actuation velocity ratios, the bistability suppression can lead to a drag reduction up to 2.5% with an energy consumption evaluated to be less than 0.6% of the aerodynamic power saving for the worst investigated case.
The paper addresses a robust navigation strategy of a rotorcraft class having a simple robotic arm to perform rapid in-flight retrieving operations in presence of wind gusts and aerodynamic effects. The target-acquiring trajectory planner is based on a cosinusoidal dynamic pattern. The mathematical model is extended to account not only the dynamics of the robotic arm but also the aerodynamics. The navigation control scheme is based on a soft integral slidingmode control (ISC) to stabilize both inner-and outer-loop dynamics regarding the rejection of not only the dynamic couplings but also aerodynamic disturbances. Detailed simulations including realistic aerodynamic effects results show the validity of the proposed navigation strategy while tracking the objectto-retrieve trajectory.
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