Experimental Investigation of Tip Vortex Meandering in the Near Wake of a Horizontal-Axis Wind Turbine

The aerodynamic optimization of horizontal axis wind turbine has became one of the most important challenge in the renewable energy field. Over the past few years, many researchers have drawn more attention to the physical processes of the wind energy conversion and precisely the identification of the main causes of energy losses. This paper presents an experimental investigation of near wake dynamics for a model horizontal axis wind turbine in a wind tunnel. The coherent structures downstream of the rotor were studied for different tip speed ratios using the Particle Image Velocimetry (PIV) technique. The influence of the tip vortex meandering was discussed and analyzed using the Proper Orthogonal Decomposition (POD) method. The high-energy modes show that radial meandering is the most energetic source of perturbation in each tip vortex sub-region. The energy fraction of these modes increase gradually during the development of the helical tip vortex filament, which confirm the growth of vortex wandering amplitude in the near wake

Proper Orthogonal Decomposition Analysis of an Airfoil Performances under a Small Vortical Gust

This paper investigates the performance of a non-symmetric airfoil in a perturbed flow for a low Reynolds number by creating small vortical structures. A newly designed two-dimensional numerical tool is used to examine the interaction between the NACA 23015 airfoil and the vortex shedding from a square cylinder. Different airfoil position ratios are numerically simulated concerning the square cylinder G/D (D: square cylinder diameter), the channel centerline T/d (d=D/2), and the vortices scale size D/c (c: airfoil chord length). Results show that the maximum values of the lift and drag aerodynamic coefficients are influenced by the airfoil’s lateral and longitudinal positions. The Proper Orthogonal Decomposition (POD) method is used to identify the most energetic flow structures. For all simulated scenarios, it was found that the first two modes reflect the dominating coherent structures in the flow field. The results also show that a leading-edge vortex is formed over the airfoil. The observed phenomena of symmetric and antisymmetric shedding vortex mechanisms essentially depend on the lateral distance of the airfoil T/d and the vortex scale size D/c. However, the spectral analysis demonstrates that the shedding frequency mainly depends on the gap distance G/D

Performance evaluation of cup-anemometers and wind speed characteristics analysis

The objective of the present work is to study the performance of cup-anemometers installed at different heights on a 40 m tall wind mast over an approximate period of 55 months between September 13, 2005 and May 09, 2010. The performance of co-located cup anemometers has been analyzed by calculating the annual mean, median, standard deviation, tower distortion factor (TDF), scatter factor (SCF), and developing linear correlations between the co-located sensors. The study showed that the performance of sensors did not deteriorate much with time but slightly higher values of TDF were obtained with passage of time. The annual mean wind speeds, the median values and the standard deviations were almost the same during different years and were comparable with co-located sensors at each height. The SCF values were found to be increasing with decreasing height of wind speed measurements. Finally, a total of 16 wind turbines of 2 MW rated capacity each were used to find the most suitable wind turbine for the location under investigation.Research Institute of King Fahd University of Petroleum and Minerals,Dhahran, Saudi Arabia.http://www.elsevier.com/locate/renene2017-02-28hb201