Wind energy is the fastest growing alternate source of energy in the world since its purely economic potential is complemented by its great positive environmental impact. The wind turbine, whether it may be a Horizontal-Axis Wind Turbine (HAWT) or a Vertical-Axis Wind Turbine (VAWT), offers a practical way to convert the wind energy into electrical or mechanical energy. Although this book focuses on the aerodynamic design and performance of VAWTs based on the Darrieus concept, it also discusses the comparison between HAWTs and VAWTs, future trends in design and the inherent socio-economic and environmental friendly aspects of wind energy as an alternate source of energy.

Wind turbine design with emphasis on Darrieus concept Ion Paraschivoiu

Numerical investigations on dynamic stall of low Reynolds number flow around oscillating airfoils

The aerodynamic behavior of a vertical axis wind turbine (VAWT) is analyzed by means of 2D particle image velocimetry (PIV), focusing on the development of dynamic stall at different tip speed ratios. The VAWT has an unsteady aerodynamic behavior due to the variation with the azimuth angle θ of the blade’s sections’ angle of attack, perceived velocity and Reynolds number. The phenomenon of dynamic stall is then an inherent effect of the operation of a VAWT at low tip speed ratios, impacting both loads and power. The present work is driven by the need to understand this phenomenon, by visualizing and quantifying it, and to create a database for model validation. The experimental method uses PIV to visualize the development of the flow over the suction side of the airfoil for two different reference Reynolds numbers and three tip speed ratios in the operational regime of a small urban wind turbine. The field-of-view of the experiment covers the entire rotation of the blade and almost the entire rotor area. The analysis describes the evolution of the flow around the airfoil and in the rotor area, with special focus on the leading edge separation vortex and trailing edge shed vorticity development. The method also allows the quantification of the flow, both the velocity field and the vorticity/circulation (only the results of the vorticity/circulation distribution are presented), in terms of the phase locked average and the random component.

/pdf/visualization-by-piv-of-dynamic-stall-on-a-vertical-axis-1iokxta8do.pdf

Visualization by PIV of dynamic stall on a vertical axis wind turbine

https://pure.tue.nl/ws/files/55479574/1_s2.0_S0960148117300848_main.pdf

CFD simulation of a vertical axis wind turbine operating at a moderate tip speed ratio: guidelines for minimum domain size and azimuthal increment

https://cyberleninka.org/article/n/450829.pdf

2D CFD Modeling of H-Darrieus Wind Turbines Using a Transition Turbulence Model

The implementation of wind energy conversion systems in the built environment renewed the interest and the research on Vertical Axis Wind Turbines (VAWT), which in this application present several advantages over Horizontal Axis Wind Turbines (HAWT). The VAWT has an inherent unsteady aerodynamic behavior due to the variation of angle of attack with the angle of rotation, perceived velocity and consequentially Reynolds number. The phenomenon of dynamic stall is then an intrinsic effect of the operation of a Vertical Axis Wind Turbine at low tip speed ratios, having a significant impact in both loads and power. The complexity of the unsteady aerodynamics of the VAWT makes it extremely attractive to be analyzed using Computational Fluid Dynamics (CFD) models, where an approximation of the continuity and momentum equations of the Navier-Stokes equations set is solved. The complexity of the problem and the need for new design approaches for VAWT for the built environment has driven the authors of this work to focus the research of CFD modeling of VAWT on: •comparing the results between commonly used turbulence models: URANS (Spalart-Allmaras and k-) and large eddy models (Large Eddy Simulation and Detached Eddy Simulation) •verifying the sensitivity of the model to its grid refinement (space and time), •evaluating the suitability of using Particle Image Velocimetry (PIV) experimental data for model validation. The 2D model created represents the middle section of a single bladed VAWT with infinite aspect ratio. The model simulates the experimental work of flow field measurement using Particle Image Velocimetry by Simao Ferreira et al for a single bladed VAWT. The results show the suitability of the PIV data for the validation of the model, the need for accurate simulation of the large eddies and the sensitivity of the model to grid refinement.

/pdf/simulating-dynamic-stall-in-a-2d-vawt-modeling-strategy-3tlg5x92ga.pdf

Simulating Dynamic Stall in a 2D VAWT: Modeling strategy, verification and validation with Particle Image Velocimetry data

One of the results of the development of wind energy conversion solutions for the built environment is the reappearance of Vertical Axis Wind Turbines (VAWTs). The application of wind turbines in urban environments presents design challenges driven by the complex wind fields experienced in the urban boundary layer. Urban Wind Turbines operate near, on and in the wake of bluff bodies larger than the rotor scale. These flow conditions might result in skewed flow operation. The objective of the current paper is to bring insight into the development of the near wake of a H-VAWT in skewed flow, namely understanding:  Blade loading asymmetry in spanwise direction.  Trajectory of the tip vortices, including inboard movement and radial expansion of the shed and trailing vorticity.  Asymmetry of the wake in spanwise direction.  Blade vortex interaction of upwind tip vortex with downwind blade passage.  Load distribution in downwind blade passage.  Effect of skew in the expansion of the mid-wake. The investigation is composed of experimental wind tunnel research of a two bladed H-Darrieus VAWT model with Particle Image Velocimetry, and modeling of the rotor and wake with a 3D unsteady panel method. Simulations of the rotor in skewed flow are validated with the experimental PIV data and with the torque measurements of 1 and 2 . The results of the panel model, validated by experiments, show the impact of skew angle on the near wake’s development, both for the upwind blade passage as well as the downwind blade passage.

/pdf/the-vawt-in-skew-stereo-piv-and-vortex-modeling-1j22a8tlsf.pdf

Cjs Ferreira

Papers

Simulating Dynamic Stall in a 2D VAWT: Modeling strategy, verification and validation with Particle Image Velocimetry data

The VAWT in Skew: Stereo-PIV and Vortex Modeling