The purpose of this paper is to investigate the feasibility of using dielectric barrier discharge plasma actuation for the pitch stability control of a National Advisory Committee for Aeronautics 0012 pitch oscillating airfoil at low Reynolds number. The effects of the plasma actuator on the flow are incorporated into Navier–Stokes equations as a body force source term. The plasma body force is modeled by a phenomenological approach. Solutions are obtained by two-dimensional numerical simulations using the $\gamma -{\text{Re}}_{\theta }$ transition model. The flow control effects of plasma actuator locations, strengths, force directions, and laminar separation flutter (LSF) conditions are investigated. The energy extracted by the airfoil from the flow over one oscillation cycle is defined to evaluate the control performance. The LSF analysis based on energy maps is also implemented. The control effect of co-flow plasma configuration on pitch instability is better than the counterflow configuration. The co-flow plasma actuator located at 0.6c reaches the best control performance and the energy extracted by the airfoil from the flow over one oscillation cycle reduces by 726% relative to the baseline case. The flow feature inducing the pitch instability and the flow control mechanism of co-flow and counterflow plasma actuator is analyzed in terms of the flow structure and pressure distribution, respectively. The results show that the plasma flow control is effective to mitigate the pitch instability across a wide range of Reynolds numbers at which laminar separation flutter occurs without control.

Flow-induced vibrations (FIVs) can be utilized to harvest energy for micro-aerial vehicles. The purpose of this paper is to investigate the fluid–structure interaction in piezoelectric energy harvesting. A piezoelectric energy harvester for a membrane wing at Reynolds number Re = 8000 is studied based on an aero-electro-mechanical model using the computational fluid dynamics/computational structure dynamic coupling method. The updated Lagrangian formulation is applied for the large deformation of the flexible structure. The effects of the location of piezoelectric harvesters and the angle of attack ($\alpha =4^{\circ }–24°$ ) on FIV response and energy harvesting performance are investigated. Average power density is defined to evaluate the energy harvesting performance of the harvester. The location of the piezoelectric harvester has a negligible effect on the energy harvesting performance under the same FIV response. However, the change in local stiffness caused by the location of the piezoelectric harvester may induce a noticeable difference in FIV response which impacts the energy harvesting performance. The simulation results indicate the strong coupling relationship among flow field, membrane structure, and electric field. There are two states of fluid–structure interaction at the angles of attack investigated. At $\alpha =4°–12°$ , the vibration response of the membrane wing is mainly driven by the natural frequency of the structure. At $\alpha =16°–24°$ , the convection and shedding of leading- and trailing-edge vortices play a dominant role in FIV response. The work presents the mechanism of fluid–structure interaction in energy harvesting from FIVs and provides a significant basis for designing energy harvesters of membrane wings.

Stall flutter is a large-amplitude, flow-induced limit cycle oscillation that poses a risk of structural failure of wings. In this paper, a numerical investigation is conducted to explore the mitigation of stall flutter using active surface morphing with a single-mode harmonic motion at a Reynolds number of 1000. The effects of oscillation position and phase on mitigation are evaluated based on the net energy gain of the airfoil over one oscillation cycle. The results show the effectiveness of active surface morphing in mitigating stall flutter, achieving a maximum of 46% reduction in energy obtained by the airfoil from the flow. The control effect is primarily attributed to the decrease in the aerodynamic moment peak during the pitch-up phase and the increase in the aerodynamic moment trough during the pitch-down phase. The former is essentially due to the large-scale clockwise vortex induced by the skin bulging in the pitch-up phase. The latter is fundamentally caused by the weakening of the trailing-edge vortex and the strengthening of the second leading-edge vortex. Finally, maps depicting the energy exchange between the flow and the airfoil system are presented to further demonstrate the control effectiveness of active surface morphing.

This paper investigates the effect of wingtip bending morphing on gust-induced aerodynamics based on the fluid–structure interaction (FSI) method at Re = 40 000. First, an explicit spatiotemporal numerical model for a wingtip bending morphing on a wing with a semi-aspect ratio of 4 is deduced, considering geometrical nonlinearity under large morphing amplitude. A modal-based FSI framework is developed to consider the elastic deformation, active wingtip morphing, and gust. The shear-stress transport-γ model is introduced. The above FSI method is validated by gust response experimental results. The mitigation effects of active bending morphing on gust-induced aerodynamics at different phase offset, gust ratios (GR), and flare angles are investigated. Under GR = 0.2 and flare angle = 0, wingtip bending morphing achieves the best mitigation effect when the phase offset is π/2. As GR increases to 0.4, the optimum phase offset shifts to π/3 and the alleviation rate decreases. The mitigation rate increases with the flare angle. Under GR = 0.4 and flare angle = 30°, the optimum phase offset is π/6, in which case the lift response is reduced by 37%, and wing root bending moment response is reduced by 73% relative to the baseline case. The flow field and vortex evolution result infers that the wingtip bending morphing decreases the spanwise width of the leading-edge vortex and reduces the area of low-pressure zones on the suction side, thereby mitigating gust-induced aerodynamics. The results indicate that active wingtip bending morphing has great potential for gust load alleviation for future aircraft.