Airfoil

About: Airfoil is a research topic. Over the lifetime, 24696 publications have been published within this topic receiving 337709 citations. The topic is also known as: aerofoil & wing section.

Modeling and analysis of piezoaeroelastic energy harvesters

Abstract: This work investigates the influence of structural and aerodynamic nonlinearities on the dynamic behavior of a piezoaeroelastic system. The system is composed of a rigid airfoil supported by nonlinear torsional and flexural springs in the pitch and plunge motions, respectively, with a piezoelectric coupling attached to the plunge degree of freedom. The analysis shows that the effect of the electrical load resistance on the flutter speed is negligible in comparison to the effects of the linear spring coefficients. The effects of aerodynamic nonlinearities and nonlinear plunge and pitch spring coefficients on the system’s stability near the bifurcation are determined from the nonlinear normal form. This is useful to characterize the effects of different parameters on the system’s output and ensure that subcritical or “catastrophic” bifurcation does not take place. Numerical solutions of the coupled equations for two different configurations are then performed to determine the effects of varying the load resistance and the nonlinear spring coefficients on the limit-cycle oscillations (LCO) in the pitch and plunge motions, the voltage output and the harvested power.

Aerodynamic and Aeroelastic Characteristics of Wings with Conformal Control Surfaces for Morphing Aircraft

Abstract: Investigations are conducted on lifting surfaces with conventional and conformal trailing-edge control surfaces. The Sohngen inversion formula is used with the thin-airfoil integral equation to determine the aerodynamic pressure for various control surface chord-to-airfoil chord ratios. Comparisons to a conventional control surface show increases in lift and pitching moment of the airfoil with a conformal control surface. Aerodynamic pressure distributions acting on a wing with control surfaces are determined with the vortex lattice technique. Predicted aerodynamic pressures and roll moments are compared to available wind-tunnel data and provide a more general understanding of theaerodynamicbehavior observed there. Roll performance of a rectangular wing is determined for various control surface chord-to-wing chord ratios. It is found that the maximum roll rate is greater for a wing with a conformal control surface, but has a lower reversal dynamic pressure than the wing with a conventional control surface. The aerodynamic and aeroelastic results obtained from this investigation provide some insight for wings designed with conformal control surfaces.

A Quasi-Vortex-Lattice Method in Thin Wing Theory

Abstract: A quasi-continuous method is developed for solving thin-wing problems. For the purpose of satisfying the wing boundary conditions, the spanwise vortex distribution is assumed to be stepwise-constant, while the chordwise vortex integral is reduced to a finite sum through a modified trapezoidal rule and the theory of Chebyshev polynomials. Wing-edge and Cauchy singularities are acounted for. The total aerodynamic characteristics are obtained by an appropriate quadrature integration. The two-dimensional results for airfoils without flap deflection reproduce the exact solutions in lift and pitching moment coefficients, the leading edge suction, and the pressure difference at a finite number of points. For a flapped airfoil, the present results are more accurate than those given by the vortex-lattice method. The three-dimensional results also show an improvement over the results of the vortex-lattice method. Extension to nonplanar applications is discussed.

Air foil and bridge deck flutter derivatives

Abstract: THE FLUTTER PHENOMENA OF THE SUSPENSION BRIDGE IS COMPARED TO THE AIRFOIL. A FREE-OSCILLATION EXPERIMENTAL METHOD IS USED TO MEASURE MODEL BRIDGE FLUTTER COEFFICIENTS ANALOGOUS TO AIRFOIL FLUTTER COEFFICIENTS. THE AIRFOIL IS EMPLOYED AS A CHECK ON THE EXPERIMENTAL METHOD, BOTH AS A THEORETICAL BAKCDROP AND TO TEST OUT THE NATURE OF AERODYNAMIC OSCILLATORY FORCES UNDER EXPONENTIALLY MODIFIED MOTION. A SHORT CATALOGUE OF BRIDGE DECK FLUTTER COEFFICIENTS WAS EXPERIMENTALLY OBTAINED AND COVERS A RANGE OF BRIDGE DECK FORMS. DETAILED RESULTS ARE DESCRIBED TO ACCOUNT FOR A NUMBER OF PHENOMENA OBSERVED IN THE WIND TUNNEL AND IN THE FIELD. /AUTHOR/

Origin of transonic buffet on airfoils.

Abstract: Buffeting flow on transonic aerofoils serves as a model problem for the more complex three-dimensional flows responsible for aeroplane buffet. The origins of transonic aerofoil buffet are linked to a global instability, which leads to shock oscillations and dramatic lift fluctuations. The problem is analysed using the Reynoldsaveraged Navier–Stokes equations, which for the foreseeable future are a necessary approximation to cover the high Reynolds numbers at which transonic buffet occurs. These equations have been shown to reproduce the key physics of transonic aerofoil flows. Results from global-stability analysis are shown to be in good agreement with experiments and numerical simulations. The stability boundary, as a function of the Mach number and angle of attack, consists of an upper and a lower branch – the lower branch shows features consistent with a supercritical bifurcation. The unstable modes provide insight into the basic character of buffeting flow at nearcritical conditions and are consistent with fully nonlinear simulations. The results provide further evidence linking the transonic buffet onset to a global instability.