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.

Multi-Element High-Lift Configuration Design Optimization Using Viscous Continuous Adjoint Method

Abstract: An adjoint-based Navier‐Stokes design and optimization method for two-dimensional multi-element high-lift configurations is derived and presented. The compressible Reynolds-averaged Navier‐Stokes equations are used as a flow model together with the Spalart‐Allmaras turbulence model to account for high Reynolds number effects. When a viscous continuous adjoint formulation is used, the necessary aerodynamic gradient information is obtained with large computational savings over traditional finite difference methods. The high-lift configuration parallel design method uses a point-to-point matched multiblock grid system and the message passing interface standard for communication in both the flow and adjoint calculations. Airfoil shape, element positioning, and angle of attack are used as design variables. The prediction of high-lift flows around a baseline three-element airfoil configuration, denoted as 30P30N, is validated by comparison with available experimental data. Finally, several design results that verify the potential of the method for high-lift system design and optimization are presented. The design examples include a multi-element inverse design problem and the following optimization problems: lift coefficient maximization, lift-to-drag ratio maximization, and the maximum lift coefficient maximization problem for both the RAE2822 single-element airfoil and the 30P30N multi-element airfoil.

A Feasibility Study To Control Airfoil Shape Using THUNDER

Abstract: The objective of this study was to assess the capabilities of a new out-of-plane displacement piezoelectric actuator called thin-layer composite-unimorph ferroelectric driver and sensor (THUNDER) to alter the upper surface geometry of a subscale airfoil to enhance performance under aerodynamic loading. Sixty test conditions, consisting of combinations of five angles of attack, four dc applied voltages, and three tunnel velocities, were studied in a tabletop wind tunnel. Results indicated that larger magnitudes of applied voltage produced larger wafer displacements. Wind-off displacements were also consistently larger than wind-on. Higher velocities produced larger displacements than lower velocities because of increased upper surface suction. Increased suction also resulted in larger displacements at higher angles of attack. Creep and hysteresis of the wafer, which were identified at each test condition, contributed to larger negative displacements for all negative applied voltages and larger positive displacements for the smaller positive applied voltage (+102 V). An elastic membrane used to hold the wafer to the upper surface hindered displacements at the larger positive applied voltage (+170 V). Both creep and hysteresis appeared bounded based on the analysis of several displacement cycles. These results show that THUNDER can be used to alter the camber of a small airfoil under aerodynamic loads.

Flutter-Boundary Identification for Time-Domain Computational Aeroelasticity

Abstract: Three time-domain damping/frequency/flutter identification techniques are discussed; namely, the moving-block approach, the least-squares curve-fitting method, and a system-identification technique using an autoregressive moving-average model of the aeroelastic system. These methods are evaluated for use with time-intensive computational aeroelastic simulations, represented by the aeroelastic transient responses of a double-wedge airfoil and three-dimensional wing in hypersonic flow. The responses are generated using the NASA Langley CFL3D computational aeroelastic code, in which the aerodynamic loads are computed from the unsteady Navier-Stokes equations. In general, the methods agree well. The system-identification technique, however, provided quick damping and frequency estimates with minimal response-record length. In the present case, the computational cost required to generate each aeroelastic transient was reduced by 75%. Finally, a flutter margin for discrete-time systems, constructed using the autoregressive moving-average approach, is evaluated for use in the hypersonic flow regime for the first time. For the binary-mode case, the flutter margin exhibited a linear correlation with dynamic pressure, minimizing the number of responses required to locate flutter. However, the flutter margin was not linear for the multimode system, indicating that it does not perform as expected in all cases.

Influence of Finite Span and Sweep on Active Flow Control Efficacy

Abstract: Active flow control efficacy was investigated by means of leading-edge and flap-shoulder zero mass-flux blowing slots on a semispan wing model that was tested in unswept (standard) and swept configurations. On the standard configuration, stall commenced inboard, but with sweep the wing stalled initially near the tip. On both configurations, leading-edge perturbations increased CL,max and post stall lift, both with and without deflected flaps. Without sweep, the effect of control was approximately uniform across the wing span but remained effective to high angles of attack near the tip; when sweep was introduced a significant effect was noted inboard, but this effect degraded along the span and produced virtually no meaningful lift enhancement near the tip, irrespective of the tip configuration. In the former case, control strengthened the wingtip vortex; in the latter case, a simple semi-empirical model, based on the trajectory or "streamline" of the evolving perturbation, served to explain the observations. In the absence of sweep, control on finite-span flaps did not differ significantly from their nominally twodimensional counterpart. Control from the flap produced expected lift enhancement and CL,max improvements in the absence of sweep, but these improvements degraded with the introduction of sweep.

Computational Investigation of Finite Width Microtabs for Aerodynamic Load Control

Abstract: The use of deployable microtabs on wind turbine blades has been proposed for the purpose of active load control. A great deal of two-dimensional wind tunnel testing and CFD simulation has already been conducted to study the effects of tabs on the aerodynamic performance characteristics of airfoil sections. This paper presents a literature survey of existing studies that have looked at the effects of introducing gaps and serrations to the tabs. Such treatments are found to allow modulation of the lift enhancing properties of the tab. Three-dimensional Reynolds-averaged Navier-Stokes calculations of various tabgap configurations applied to an airfoil are described, and results are presented. The relationship between tab solidity ratio and increments in lift is found to be highly linear. Such a relationship could be significant for the development of future microtab deployment systems.