Transonic flight has high economic benefits, but the appearance of transonic buffet limits the flight envelope. The shock control bump currently used for transonic buffet suppression tends to degrade the aerodynamic performance of the non-buffeting state. In this study, a smart skin system is used to eliminate the fluctuating load of transonic buffet by measuring the airfoil lift coefficient as the feedback signal and adjusting the local skin height using data-driven, model-free adaptive control. Since the actuator height is dynamically adjusted only after the occurrence of transonic buffet, the smart skin can completely suppress the fluctuating load and does not affect the aerodynamic performance in the non-buffeting state. The suppression effect of the proposed smart skin on transonic buffet is verified by numerical simulation of the flow. The simulation results show that due to the introduction of closed-loop control, the fluctuating load of transonic buffet can be effectively suppressed for different positions and maximum heights of the actuator. Even when the flow state changes, the robust smart skin system can also achieve the control goal. Therefore, smart skins combining flexible materials and control technologies have the potential to effectively improve the aerodynamic performance of aircraft.
Transonic buffeting can induce strong noise and reduce aircraft lifespan. In view of the complexity of transonic buffeting flow, this study combines the highly accurate Delayed-Detached Eddy Simulation (DDES) and Discrete Frequency Response (DFR) method to analyze the flow field and sound propagation law in different buffeting states, and also investigates its noise generating characteristics by Dynamic Mode Decomposition (DMD) and Pearson correlation. It is found that the low-frequency and small-amplitude shock oscillation of light buffeting state is insufficient to trigger large separated flow. Besides, the reattachment phenomenon occurs in the trailing-edge, which is the second mode of boundary layer separation, corresponding to the lower Sound Pressure Levels (SPL). In deep buffeting state, however, the shock oscillates with high frequency and large amplitude, producing large separated bubbles without the reattachment phenomenon, which is the first mode of boundary layer separation. Moreover, there is a large-scale vortex structure with high energy content in the recirculation zone, which develops towards the trailing-edge under the action of convection and produces strong Upstream Traveling Waves (UTWs). Collision occurs between UTWs and the shock wave oscillation. In this process, they promote each other, which increases the shock wave oscillation frequency and SPL. This state is not the superposition effect of buffeting and stall. And its main sound sources are shock oscillation and the von Kármán mode.
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