**Aerodynamic modeling of floating vertical axis wind turbines using the actuator cylinder flow method**

*Zhengshun Chenga, Helge Aagaard Madsend, Zhen Gaoa, Torgeir Moan, Energy Procedia, January 2016*

Recently the interest in developing vertical axis wind turbines (VAWTs) for offshore application has been increasing. Among the aerodynamic models of VAWTs, double multi-streamtube (DMST) and actuator cylinder (AC) models are two favorable methods for fully coupled modeling and dynamic analysis of floating VAWTs in view of accuracy and computational cost. This paper deals with the development of an aerodynamic code to model floating VAWTs using the AC method developed by Madsen. It includes the tangential load term when calculating induced velocities, addresses two different approaches to calculate the normal and tangential loads acting on the rotor, and proposes a new modified linear solution to correct the linear solution.

**A Low-Reynolds-Number, High-Angle-of-Attack Investigation of Wind Turbine Aerofoils**

* S Worasinchai, G Ingram and R Dominy*, *SAGE and Institution of Mechanical Engineers, 18 July 2011*

This article describes an experimental, aerodynamic investigation of four aerofoils intended for small wind turbine applications. The aerofoils of these small machines (both horizontal and vertical axes) normally experience conditions that are quite different from large-scale machines due to smaller chord length and lower wind speed, resulting in significantly lower Reynolds numbers. They also operate with an unusually wide range of incidence angles (0° to 90° for horizontal axis and 0° to 360° for vertical axis). Four appropriate aerofoils were chosen for testing at three Reynolds numbers (65000, 90000, and 150000) through 360° incidence to cover almost all possible conditions that might be encountered by both types of turbines...

**A Model for the Response of Vertical Axis Wind Turbines to Turbulent Flow Parts 1 and 2**

* David R. Malcolm, Sandia National Laboratories, July 1988*

This report describes a project intended to incorporate the effects of atmospheric turbulence into the structural .response of Darrieus rotor, vertical axis wind turbines. The basis of the technique is the generation of a suitable time series of wind velocities, which are passed through a double multiple streamtube aerodynamic representation of the rotor. The aerodynamic loads are decomposed into components of the real eigenvectors of the rotor and subsequently into full-power and cross-spectral densities. These modal spectra are submitted as input to a modified NASTRAN random load analysis and the power spectra of selected responses are obtained. This procedure appears to be successful. Results at zero...

**Comparison of aerodynamic models for Vertical Axis Wind Turbine**

*C Simão Ferreira et al 2014*

Multi-megawatt Vertical Axis Wind Turbines (VAWTs) are experiencing an increased interest for floating off-shore applications. However, VAWT development is hindered by the lack of fast, accurate and validated simulation models. This work compares six different numerical models for VAWTS: a multiple streamtube model, a double-multiple streamtube

model, the actuator cylinder model, a 2D potential ow panel model, a 3D unsteady lifting line model, and a 2D conformal mapping unsteady vortex model. The comparison covers rotor configurations with two NACA0015 blades, for several tip speed ratios, rotor solidity and fixed pitch angle, included heavily loaded rotors, in inviscid flow.

**Computational and Experimental Study on Vertical Axis Wind Turbine In Search For An Efficient Design**

*Mohammad M. Bashar, Georgia Southern University, 2014*

Wind alone can fulfill most of the energy requirement of the world by its efficient conversion in to energy. Though Horizontal Axis Wind Turbine (HAWT) is more popular but needs high wind speed to generate energy. On the other hand Vertical Axis Wind Turbine (VAWT) needs low wind speed and can be installed anywhere which are some of the reasons for this research. The main objective of this research is to improve the design and performance of VAWT to make it more attractive, efficient, durable and sustainable. For a VAWT the blades perform the main role to extract energy from the wind. Airfoil is considered as the blade for this new design of VAWT. Airfoil has some good aerodynamic characteristics, match with...

**Effect Of The Shaft On The Aerodynamic Performance Of Urban Vertical Axis Wind Turbines**

*Abdolrahim Rezaelha, Ivo Kalkman, Hamid Montazeri, Bert Blocken, Elsevier Ltd, October 2017 *

The central shaft is an inseparable part of a vertical axis wind turbine (VAWT). For small turbines such as those typically used in urban environments, the shaft could operate in the subcritical regime, resulting in large drag and considerable aerodynamic power loss. The current study aims to (i) quantify the turbine power loss due to the presence of the shaft for different shaft-to-turbine diameter ratios *δ* from 0 to 16%, (ii) investigate the impact of different operational and geometrical parameters on the quantified power loss and (iii) evaluate the impact of the addition of surface roughness on turbine performance improvement. Unsteady Reynolds-averaged Navier-Stokes (URANS) calculations are...

**Fish schooling as a basis for vertical axis wind turbine farm design***

*Robert Whittlesey, Sebastian Liska, and John Dabiri, California Institute of Technology, February 11, 2010*

Most wind farms consist of horizontal axis wind turbines (HAWTs) due to the high power coefficient (mechanical power output divided by the power of the free-stream air through the turbine cross-sectional area) of an isolated turbine. However when in close proximity to neighbouring turbines, HAWTs suffer from a reduced power coeffi- cient. In contrast, previous research on vertical axis wind turbines (VAWTs) suggests that closely-spaced VAWTs may experience only small decreases (or even increases) in an individual turbine’s power coefficient when placed in close proximity to neighbours, thus yielding much higher power outputs for a given area of land...

**Measurements and Calculations of Aerodynamic Torques for a Vertical Axis Wind Turbine**

* Robert E. Akins, Dale E. Berg, W. Tait Cyrus*, *Sandia National Labs, October 1987*

This report describes measurements of aerodynamic torque on a vertical-axis wind turbine. Accelerometers mounted at the equator of the rotor and a torque meter mounted at the base of the rotor were used to compute the net aerodynamic torque acting on the rotor. Assumptions concerning blade- response symmetry were required to achieve blade torque as a function of rotor position on each half of a revolution for a two-bladed rotor. Results are presented for tip-speed ratios from 2.5 to 8.0 for two turbine rotational speeds. Evidence of dynamic stall is observed at low tip-speed ratios.

*Saman Naghib Zadeh, Matin Komeili and Marius ParaschivoiuMechanical and Industrial Engineering, Concordia University, September 2014*

Mesh resolution requirements are investigated for 2-D and 3-D simulations of the complex flow around a straight-blade vertical axis wind turbine (VAWT). The resulting flow, which may include large separation flows over the blades, dynamic stall, and wake-blade interaction, is simulated by an Unsteady Reynolds- Averaged Navier–Stokes analysis, based on the Spalart–Allmaras (S–A) turbulence model. A grid resolution study is conducted on 2-D grids to examine the convergence of the CFD model. Hence, an averaged grid residual of y+ > 30 is employed, along with a wall treatment, to capture the near-wall region’s flow structures. Furthermore a 3-D simulation on a coarse grid of the VAWT model is performed in order to explore the influence of the 3-D effects on the aerodynamic performance of the turbine. Finally, based on the 2-D grid convergence study and the 3-D results, the required computational time and mesh to simulate 3-D VAWT accurately is proposed.

**Modeling Stochastic Wind Loads on Vertical Axis Wind Turbines**

*Paul S. Veers, Sandia National Laboratories, September 1984*

The Vertical AXIS Wind Turbine (VAWT) is a machine which extracts energy from the wind. Since random turbulence is always present, the effect of this turbulence on the wind turbine fatigue life must be evaluated. This problem is approached by numerically simulating the turbulence and calculating, In the time domain, the aerodynamic loads on the turbine blades. These loads are reduced to the form of power and cross spectral densities which can be used in standard linear structural analysis codes. The relative importance of the turbulence on blade loads is determined.

*Gregory F. Homicz, Sandia National Laboratories, September 1991*

Blade fatigue life is an important element in determining the economic viability of the VerticalAxis Wind Turbine (VAWT). A principal source of blade fatigue is thought to be the stochastic (i.e., random) aerodynamic loads created by atmospheric turbulence. This report describes the theoretical background of the VAWT Stochastic Aerodynamic Loads (VAWT-SAL) computer code, whose purpose is to numerically simulate these random loads, given the rotor geometry, operating conditions, and assumed turbulence properties. A Double-Multiple-StreamTube (DMST) analysis is employed to model the rotor’s aerodynamic response. The analysis includes the effects of Reynolds number variations, different airfoil sections and...

**The Influence Of Blade Roughness On The Performance Of A Vertical Axis Tidal Turbine**

*Luis Priegue, Thorsten Stoesser Elsevier Ltd, April 2017*

This paper reports the findings of an experimental study investigating the influence of blade roughness on the performance of a vertical axis tidal turbine. Due to their design, vertical axis turbines undergo periods of stall, i.e. flow separation from the blade, during each revolution. It is hypothesised that roughening turbine blades delays flow separation (in analogy to flows over rough bluff bodies) and hence diminishes turbine stall which in turn should result in an increase in turbine performance. Laboratory experiments were undertaken in Cardiff University’s hydraulics laboratory, testing vertical axis turbines with rotors comprising smooth and rough blades.

*Abdolrahim Rezaeiha, Hamid Montazeri, Bert Blocken, Elsevier Ltd., December 01, 2017*

The accuracy of CFD simulations of vertical axis wind turbines (VAWTs) is known to be significantly associated with the computational parameters, such as azimuthal increment, domain size and number of turbine revolu- tions before reaching a statistically steady state condition (convergence). A detailed review of the literature, however, indicates that there is a lack of extensive parametric studies investigating the impact of the computational parameters. The current study, therefore, intends to systematically investigate the impact of these parameters, on the simulation results to guide the execution of accurate CFD simulations of VAWTs at different tip speed ratios (λ) and solidities (σ)...

**Unsteady Flow Numerical Simulation of Vertical Axis Wind Turbine**

*Du Gang, Wu Chun Kau, Elsevier Ltd, 2015 *

This paper sets up model of the flow field for vertical axis wind turbine based on airfoil DU93-W 210. FLUENT is used to solve the two dimensional unsteady incompressible N-S equations with RNG κ ε turbulence model. COUPLE algorithm and sliding mesh is used to simulate the 2-D unsteady flow field of the wind turbine. The rotor power coefficient of wind energy and the variation of the wind turbine’s total torque are analyzed under the variation of varied blade installation angle and chord length. As the result shows, the power coefficient of wind energy at the best installation angle is increased by 2%, and the power coefficient of wind energy in the best solidity is increased by 15%.

*David Malcolm, 2017*

The vertical axis wind turbine was “re-invented” in 1970 by Peter South and Raj Rangi [1] of the Canadian National Research Council, Ottawa, where much development was carried out. Considerable development was also carried out at Sandia National Laboratories, New Mexico, especially into the structural dynamics of the curved Darrieus rotor [2, 3]. It was determined that the rotating frame effects of Coriolis action, rotational softening, and pretensioning played important roles.

*C. Galinos, T.J. Larsen, H.A. Madsen, U.S. Paulsen, Department of Wind Energy, 2016*

**Wind Tunnel testing of small Vertical-Axis Wind Turbines in Turbulent Flows**

*Andreu Carbó Molina, Gianni Bartoli, Tim de Troyer, Elsevier Ltd, 2017*

This study presents an innovatinve wind tunnel approach to evluate the efficiency of Vertical-Axis Wind Turbines (VAWT) in turbulent flows, to study their integration in urban environments. The first part of the research is devoted to obtaining highly-turbulent wind profiles in the wind tunnel, with the use of different configurations of square grids. A careful study and validation of this technique is done, in order to obtain uniform wind conditions with adequate values of turbulence intensity and length scales to model the urban flows. The set-up is used to test a H-Darrieus VAWT under values of turbulence over 5%, in comparison with the operation of the turbine under free stream...