Multi-functional wind barrier based on triboelectric nanogenerator for power generation, self-powered wind speed sensing and highly efficient windshield

We present a theoretical framework to characterize the steady and unsteady aeroelastic behaviour of compliant membrane wings under different conditions. We develop an analytic model based on thin airfoil theory coupled with a membrane equation. Adopting a numerical solution to the model equations, we study the effects of wing compliance, inertia and flapping kinematics on aerodynamic performance. The effects of added mass and fluid damping on a flapping membrane are quantified using a simple damped oscillator model. As the flapping frequency is increased, membranes go through a transition from thrust to drag around the resonant frequency, and this transition is earlier for more compliant membranes. The wake also undergoes a transition from a reverse von Karman wake to a traditional von Karman wake. The wake transition frequency is predicted to be higher than the thrust–drag transition frequency for highly compliant wings.

Thrust, drag and wake structure in flapping compliant membrane wings

On the stability of two-dimensional membrane wings

We study the large-amplitude flutter of membranes (of zero bending rigidity) with vortex sheet wakes in two-dimensional inviscid fluid flows. We apply small initial deflections and track their exponential decay or growth and subsequent large-amplitude dynamics in the space of three dimensionless parameters: membrane pretension, mass density and stretching modulus. With both ends fixed, all the membranes converge to steady deflected shapes with single humps that are nearly fore-aft symmetric, except when the deformations are unrealistically large. With leading edges fixed and trailing edges free to move in the transverse direction, the membranes flutter periodically at intermediate values of mass density. As mass density increases, the motions are increasingly aperiodic, and the amplitudes increase and spatial and temporal frequencies decrease. As mass density decreases from the periodic regime, the amplitudes decrease and spatial and temporal frequencies increase until the motions become difficult to resolve numerically. With both edges free to move in the transverse direction, the membranes flutter similarly to the fixed–free case, but also translate vertically with steady, periodic or aperiodic trajectories, and with non-zero slopes that lead to small angles of attack with respect to the oncoming flow.

Large-amplitude membrane flutter in inviscid flow

Electro-aeromechanical modelling of actuated membrane wings

A review of membrane-wing aeroelasticity

On membrane-wing stability in laminar flow

A computational study of a two-dimensional membrane at low Reynolds numbers is presented. The membrane is assumed to be linearly elastic, massless and practically of zero thickness. A parametric study of the eects of membrane properties, tension, and ow conditions is presented for both steady and unsteady cases. The membrane shape and aerodynamic forces are computed by a fully viscous ow model and compared to those computed with a potential model. Steady results, obtained for small angles of attack (AoA), show that the membrane AoA and tension coecient uniquely dene the membrane equilibrium shape for both potential and viscous ow (for prescribed Reynolds number). Thus, the membrane initial slack, elasticity and pretension, which are used to compute the tension coecient, do not play an independent role in the steady cases. In these cases the parametric study concentrates on the eect of the membrane tension coecient, angle of attack, Reynolds number and shear stress. Results show that the tension coecient highly aects the membrane camber, while the AoA mostly inuences the chordwise location of the maximum camber point. The shear stress eect on the equilibrium shape was found to be negligible, and an increase in Reynolds number resulted in stall conditions at smaller AoA. The unsteady solutions, computed for large AoAs, present oscillations of the membrane structure which are due to vortex shedding. In these cases the eects of membrane elasticity, slack, pretension, angle of attack and Reynolds number are studied.

Sonya Tiomkin

Papers

On the stability of two-dimensional membrane wings

A review of membrane-wing aeroelasticity

On membrane-wing stability in laminar flow

Parametric Study of a Two-dimensional Membrane Wing in Viscous Laminar Flow

Membrane wing dynamic stability: The role of membrane mass