Influence Of Camber Research Articles

Passively morphing trailing edge design for composite tidal turbine blades

Numerical simulations and lab-scale experiments are used to evaluate three passively morphing trailing edge designs for a composite tidal turbine blade. The designs include a closed trailing edge, an open trailing edge, and a corrugated trailing edge. It is shown that geometric stiffness, as well as material stiffness, play key roles in achieving the desired deformation of the trailing edge. One trailing edge design is down-selected for further investigation via full-scale numerical simulations. These simulations demonstrate how the composite lay-up influences the morphing response of the trailing edge and its likelihood of material failure. The influence of camber is also investigated in terms of both material behaviour and hydrodynamic performance. Finally, the potential for bend-twist coupling of the laminate skins is explored.

Influence of camber on aerodynamic performance of airfoil based on CFD technology

In order to better understand the influence of camber on aerodynamic performance of airfoil, airfoil NACA0012, NACA2412, NACA4412 and NACA6412 were selected as research objects to conduct numerical simulation at 10m/s. According to lift coefficient, lift-drag ratio and airfoil pressure cloud diagram, the influence of camber on airfoil aerodynamic performance is obtained. The results show that the lift coefficient of airfoil increases with the increase of airfoil bending degree within a certain range of attack Angle. The lift-drag ratio of airfoil increases with the increase of its bending degree.

Surface curvature effects on the tonal noise of a wall-mounted finite airfoil.

This paper is concerned with the influence of camber on the noise of a wall-mounted finite airfoil with natural boundary layer transition. Tonal noise measurements taken in an aeroacoustic wind tunnel are presented for airfoils with aspect ratio of 2, NACAxx12 profile and camber between 0 and 6% at 40% chord. The results show camber is an important parameter that determines the operating conditions for which acoustic tone generation occurs and the number and intensity of the tones produced. Airfoils with 0%-2% camber have an acoustic signature that is dominated by a high amplitude primary tone, whereas the spectra of airfoils with higher camber of 4%-6% feature a more pronounced side tone structure. Tonal noise production does not collapse with lift coefficient, demonstrating that the local flow conditions influence the noise source. Tonal noise production is explained in terms of changes to mean flow topology, namely the location of flow separation, which is linked to tonal noise generation. Scaling of airfoil tonal noise is found to vary with angle of attack and pressure gradient. Empirical scaling laws for the primary tone frequency dependence on velocity are also derived for the cambered airfoils.

ON THE PERFORMANCE OF VERTICAL AXIS WIND TURBINES IN STEADY WIND UNDER VARIOUS BLADE CAMBER LEVELS

Vertical axis wind turbine (VAWT) has been shown to be more suited to small scale power production in the urban environment due to distinct advantages over its horizontal counterpart. Over the last few years, continuous improvement on its aerodynamic performance, either through experimental or numerical analysis, have been carried out by numerous researchers. VAWT performance was investigated using Computational Fluid Dynamics modeling. The influence of camber on steady wind performance was analyzed and the most efficient of all levels of blade camber studied for VAWT application was determined. Various levels of camber were imposed on to a NACA XX25 blade profile, namely: 0.5%; 1.5% (cambered close to the path of rotation); and 2%. Results revealed positive effect of incorporating a positive level of blade camber to VAWT design. The most favorable configuration for the VAWT under study was determined to be the camber level that causes the camber line to coincide with the path of the rotor rotation. The paper presents an in-depth discussion of the flow physics and wake dynamics, for the two wind cases of VAWTs, through flow visualizations and blade force analysis.

On the Role of Leading-Edge Bumps in the Control of Stall Onset in Axial Fan Blades

Taking a lead from the humpback whale flukes, characterized by a series of bumps that result in a sinusoidal-like leading edge, this paper reports on a three-dimensional numerical study of sinusoidal leading edges on cambered airfoil profiles. The turbulent flow around the cambered airfoil with the sinusoidal leading edge was computed at different angles of attack with the open source solver OpenFOAM, using two different eddy viscosity models integrated to the wall. The reported research focused on the effects of the modified leading edge in terms of lift-to-drag performance and the influence of camber on such parameters. For these reasons a comparison with a symmetric airfoil is provided. The research was primarily concerned with the elucidation of the fluid flow mechanisms induced by the bumps and the impact of those mechanisms on airfoil performance, on both symmetric and cambered profiles. The bumps on the leading edge influenced the aerodynamic performance of the airfoil, and the lift curves were found to feature an early recovery in post-stall for the symmetric profile with an additional gain in lift for the cambered profile. The bumps drove the fluid dynamic on the suction side of the airfoil, which in turn resulted in the capability to control the separation at the trailing edge in coincidence with the peak of the sinusoid at the leading edge.

Static model of a violin bow: Influence of camber and hair tension on mechanical behavior

Experienced bow makers empirically know the influence of wood, tapering, and camber on the playing and tonal qualities of a bow. However, the way each parameter affects the bow mechanical behavior is not clearly established. An in-plane finite element model is developed to highlight the link between the adjustable design parameters and the mechanical behavior of a bow. This model takes into account geometric nonlinearity as well as compliance of the hair. Its validity is discussed from measurements on a bow. Results from simulations are compared to experimental results from previous studies. The consequences of adjusting hair tension and camber are then investigated.

Dynamic stall model for wind turbine airfoils

Abstract A model is presented for aerodynamic lift of wind turbine profiles under dynamic stall. The model combines memory delay effects under attached flow with reduced lift due to flow separation under dynamic stall conditions. The model is based on a backbone curve in the form of the static lift as a function of the angle of attack. The static lift is described by two parameters, the lift at fully attached flow and the degree of attachment. A relationship between these parameters and the static lift is available from a thin plate approximation. Assuming the parameters to be known during static conditions, nonstationary effects are included by three mechanisms: a delay of the lift coefficient of fully attached flow via a second-order filter, a delay of the development of separation represented via a first-order filter, and a lift contribution due to leading edge separation also represented via a first-order filter. The latter is likely to occur during active pitch control of vibrations. It is shown that all included effects can be important when considering wind turbine blades. The proposed model is validated against test data from two load cases, one at fully attached flow conditions and one during dynamic stall conditions. The proposed model is compared with five other dynamic stall models including, among others, the Beddoes–Leishman model and the ONERA model. It is demonstrated that the proposed model performs equally well or even better than more complicated models and that the included nonstationary effects are essential for obtaining satisfactory results. Finally, the influence of camber and thickness distribution on the backbone curve are analysed. It is shown that both of these effects are adequately accounted for via the static input data.

Influence of camber on sound generation by airfoils interacting with high-frequency gusts

A theoretical model is developed for the sound generated when a convected disturbance encounters a cambered airfoil at non-zero angle of attack. The model is a generalization of a previous theory for a flat-plate airfoil, and is based on a linearization of the Euler equations about the steady, subsonic flow past the airfoil. High-frequency gusts, whose wavelengths are short compared to the airfoil chord, are considered. The airfoil camber and incidence angle are restricted so that the mean flow past the airfoil is a small perturbation to a uniform flow. The singular perturbation analysis retains the asymptotic regions present in the case of a flat-plate airfoil: local regions, which scale on the gust wavelength, at the airfoil leading and trailing edges; a ‘transition’ region behind the airfoil which is similar to the transition zone between illuminated and shadow regions in optical problems; and an outer region, far away from the airfoil edges and wake, in which the solution has a geometric-acoustics form. For the cambered airfoil, an additional asymptotic region in the form of an acoustic boundary layer adjacent to the airfoil surface is required in order to account for surface curvature effects. Parametric calculations are presented which illustrate that, like incidence angle, moderate amounts of airfoil camber can significantly affect the sound field produced by airfoil–gust interactions. Most importantly, the amount of radiated sound power is found to correlate very well with a single aerodynamic loading parameter, αeff, which is an effective mean-flow incidence angle for the airfoil leading edge.

A triangulation procedure for elastic cross sections with moderate wall thickness

A computational procedure is developed for detailed description of elastic beam cross sections of moderate wall thickness. It starts with a triangulation of the cross section followed by local polynomial representation of warping and shear stresses in each triangle. In addition to the simple section parameters such as area, elastic centre, etc., torsion stiffness, shear flexibility and the torsion extension coupling of pretwisted beams are also treated. Applications illustrating refinement of triangulation, the influence of camber on the shear flexibility of turbine blades and the shear flow in closed sections are included.

The Centre of Shear for Sections Bounded by Two Circular Arcs

In two recent notes Jacobs and Duncan considered the St. Venant torsion and flexure problems for beams of aerofoil cross section and have given methods for determining the centre of shear once the torsion function for the section has been found. The purpose of the present note is to give results for the location of the centre of shear for a limited range of cross sections bounded by two circular arcs for which the torsion function has long been known. The calculations shed some light on the relative influence of camber and thickness on the location of the centre of shear and are compared with the well known results for thin circular arc sections illustrated in the Structural Data Sheet 00.06.04.