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.

Predicting 2D Airfoil and 3D Wind Turbine Rotor Performance using a Transition Model for General CFD Codes

Abstract: *† ‡ A new correlation-based transition model has been developed, which is built strictly on local variables. As a result, the transition model is compatible with modern CFD techniques such as unstructured grids and massively parallel execution. The model is based on two transport equations, one for intermittency and one for a transition onset criterion in terms of momentum thickness Reynolds number. The proposed transport equations do not attempt to model the physics of the transition process (unlike e.g. turbulence models), but form a framework for the implementation of transition correlations into general-purpose CFD methods. The transition model was initially developed for turbomachinery and aeronautical flows. The main goal of the present paper is to validate the model for predicting transition on wind turbines. In this paper, fully turbulent and transitional computations of the 2D S809 airfoil along with a full 3D wind turbine rotor (that uses the S809 airfoil) have been accomplished. The transitional results are in good agreement with the experimental data and the transition model would appear to be well suited for the prediction of wind turbine aerodynamics.

Design and verification of the Risø-B1 airfoil family for wind turbines

Abstract: This paper presents the design and experimental verification of the Riso-B1 airfoil family for MW-s ize wind turbines with variable speed and pitch control . Seven airfoils were designed with thickness-to-chor d ratios between 15% and 53% to cover the entire span of a wind turbine blade. The airfoils were designed to have high maximum lift coefficient to allow a slender flexible blade while maintaining high aerodynamic efficiency. The design was carried out with a Riso inhouse multi disciplinary optimization tool. Wind tu nnel testing was done for Riso-B1-18 and Riso-B1-24 in t he VELUX wind tunnel, Denmark, at a Reynolds number of 1.6 ×10 6 . For both airfoils the predicted target characteristics were met. Results for Riso-B1-18 showed a maximum lift coefficient of 1.64. A standa rd case of zigzag tape leading edge roughness caused a drop in maximum lift of only 3.7%. Cases of more severe roughness caused reductions in maximum lift between 12% and 27%. Results for the Riso-B1-24 airfoil showed a maximum lift coefficient of 1.62. The standard case leading edge roughness caused a drop in maximum lift of 7.4%. Vortex generators and Gurney flaps in combination could increase maximum lift up to 2.2 (32%). NOMENCLATURE

Aerodynamic shape optimization of wing and wing-body configurations using control theory

Abstract: This paper describes the implementation of optimization techniques based on control theory for wing and wing-body design. In previous studies it was shown that control theory could be used to devise an effective optimization procedure for airfoils and wings in which the shape and the surrounding body-fitted mesh are both generated analytically, and the control is the mapping function. Recently, the method has been implemented for both potential flows and flows governed by the Euler equations using an alternative formulation which employs numerically generated grids, so that it can more easily be extended to treat general configurations. Here results are presented both for the optimization of a swept wing using an analytic mapping, and for the optimization of wing and wing-body configurations using a general mesh.

An unsteady airfoil theory applied to pitching motions validated against experiment and computation

Abstract: An inviscid theoretical method that is applicable to non-periodic motions and that accounts for large amplitudes and non-planar wakes (large-angle unsteady thin airfoil theory) is developed. A pitch-up, hold, pitch-down motion for a flat plate at Reynolds number 10,000 is studied using this theoretical method and also using computational (immersed boundary method) and experimental (water tunnel) methods. Results from theory are compared against those from computation and experiment which are also compared with each other. The variation of circulatory and apparent-mass loads as a function of pivot location for this motion is examined. The flow phenomena leading up to leading-edge vortex shedding and the limit of validity of the inviscid theory in the face of vortex-dominated flows are investigated. Also, the effect of pitch amplitude on leading-edge vortex shedding is examined, and two distinctly different vortex-dominated flows are studied using dye flow visualizations from experiment and vorticity plots from computation.

Trailing-Edge Noise Prediction Using Large-Eddy Simulation and Acoustic Analogy

Abstract: The filtered Navier-Stokes equations are used to perform the large-eddy simulation of the unsteady incompressible flow around the blunt trailing edge of a thick flat plate. The computed flow exhibits a three-dimensional vortex shedding mechanism. The frequency domain of this mechanism is in agreement with experiments and theory. In that frequency domain normalized wall-pressure levels are favorably compared to spectra measured at the blunted trailing edge of an airfoil. The far-field radiated noise is first computed via Curle's formulation, the solution of Lighthill's equation for flows embedding solid bodies. Then the theory developed by Ffowcs Williams and Hall is considered. This formulation expresses the noise generated by turbulence passing over the edge of an infinite half-plane. The suitability of this theory to the case for a thick plate is discussed. The normalized spectra of the radiated noise predicted by both methods are compared, in the frequency domain of the vortex-shedding mechanism, to airfoil noise measurements in an anechoic facility.