Double Multiple Streamtube Research Articles

3D URANS analysis of a vertical axis wind turbine in skewed flows

The paper demonstrates the potential of an unsteady RANS 3D approach to predict the effects of skewed winds on the performance of an H-type vertical-axis wind turbine (VAWT). The approach is validated through a comparison between numerical and experimental results for a full-scale Darrieus turbine, demonstrating an improved prediction ability of 3D CFD with respect to both 2D CFD and semi-empirical models based on the double multiple stream tubes method. A 3D URANS approach is then adopted to investigate the power increase observed for a straight-bladed small-scale turbine in a wind tunnel when the rotational axis is inclined from 0° to 15° from the vertical. The main advantage of this approach is a more realistic description of complex three-dimensional flow characteristics, such as dynamic stall, and the opportunity to derive local blade flow conditions on any blade portion during upwind and downwind paths. Consequently, in addition to deriving the turbine overall performance in terms of power coefficient, a better insight into the temporal and spatial evolution of the physical mechanisms is obtained. Our principal finding is that the power gain in skewed flows is obtained during the downwind phase of the revolution as the end part of the blade is less disturbed by the wake generated during the upwind phase.

A New Approach for Modeling Darrieus-Type Vertical Axis Wind Turbine Rotors Using Electrical Equivalent Circuit Analogy: Basis of Theoretical Formulations and Model Development

Models are crucial in the engineering design process because they can be used for both the optimization of design parameters and the prediction of performance. Thus, models can significantly reduce design, development and optimization costs. This paper proposes a novel equivalent electrical model for Darrieus-type vertical axis wind turbines (DTVAWTs). The proposed model was built from the mechanical description given by the Paraschivoiu double-multiple streamtube model and is based on the analogy between mechanical and electrical circuits. This work addresses the physical concepts and theoretical formulations underpinning the development of the model. After highlighting the working principle of the DTVAWT, the step-by-step development of the model is presented. For assessment purposes, simulations of aerodynamic characteristics and those of corresponding electrical components are performed and compared.

Multi-objective design optimization strategies for small-scale vertical-axis wind turbines

Extracting energy from wind has been an interesting and serious topic over the last few decades and a lot of work has been done on the subject. This paper discusses in detail possible approaches to optimization of a somewhat less known type of wind turbines, particularly suitable for small consumers. In order to perform full aerodynamic and structural shape optimization of a small-scale vertical-axis wind turbine, a Double-multiple streamtube model code, known to provide good results in stationary working regimes, was complemented by a finite element analysis and implemented into a multi-objective particle swarm algorithm. For the purpose of shortening the total time needed for aerodynamic computation, the performed numerical simulations were two-dimensional and experimentally measured static airfoil data were used. The used aerodynamic model was validated against the available experimental data of similar wind turbines. The subsequent structural analyses of the composite turbine blades were performed by applying computed maximal aerodynamic forces together with gravitational and inertial loads. By employing various input and output parameters different multi-objective optimization strategies were analyzed and compared and their applicability was demonstrated. Investigated input parameters included: wind turbine rotor diameter, blade length, chord and airfoil, composite shell thickness, laminate lay-up and ply orientations, while optimization goal functions and constraints comprised rated power, cut-in and optimal wind speed, blade mass, tip deflection, failure index and blade natural frequencies. The fidelity and accuracy of proposed methodologies can be increased by employing more complex numerical models which can easily be implemented into the code.

Aerodynamic characteristics of two-bladed H-Darrieus at various solidities and rotating speeds

Three-dimensional unsteady numerical analysis has been performed in order to analyze the aerodynamic characteristics of an H-Darrieus vertical axis wind turbine with two straight blades. The reliability of the numerical models has been demonstrated through good agreement between the calculated and measured efficiency of an H-Darrieus. Flow characteristics are closely investigated according to tip speed ratios and solidities. A comparison of aerodynamic characteristics at various operational conditions, including the maximum power point is performed. The direction of the free stream approaching the blade is considerably bent following the interaction between blade-to-blade and blade-to-free stream. Even though, the peak value of a torque increases as solidity increases, the blockage and interaction also increase, and thus, increasing the solidity alone does not improve the performance of the H-Darrieus. On the other hand, decreasing the solidity can reduce the effect of blockage and interaction, but the self-starting features via the negative torque at the low tip speed ratio becomes lost. Therefore, a theoretical model such as the DMST (double multiple stream tube) is not suitable for predicting the performance of H-Darrieus with a high solidity. The blockage by blades in the upwind revolution and the interaction between blades significantly change the magnitude of an incidence velocity, and the angle of attack. Thus, the tip speed ratio of the operation point (i.e. the highest power coefficient point) is found to be lower than it is expected.

Design and Experimental Analysis of an Exhaust Air Energy Recovery Wind Turbine Generator

A vertical axis wind turbine (VAWT) was positioned at the discharge outlet of a cooling tower electricity generator. To avoid a negative impact on the performance of the cooling tower and to optimize the turbine performance, the determination of the VAWT position in the discharge wind stream was conducted by experiment. The preferable VAWT position is where the higher wind velocity matches the positive torque area of the turbine rotation. With the proper matching among the VAWT configurations (blade number, airfoil type, operating tip-speed-ratio, etc.) and exhaust air profile, the turbine system was not only able to recover the wasted kinetic energy, it also reduced the fan motor power consumption by 4.5% and increased the cooling tower intake air flow-rate by 11%. The VAWT had a free running rotational speed of 479 rpm, power coefficient of 10.6%, and tip-speed-ratio of 1.88. The double multiple stream tube theory was used to explain the VAWT behavior in the non-uniform wind stream. For the actual size of a cooling tower with a 2.4 m outlet diameter and powered by a 7.5 kW fan motor, it was estimated that a system with two VAWTs (side-by-side) can generate 1 kW of power which is equivalent to 13% of energy recovery.

Simulating Dynamic Stall Effects for Vertical Axis Wind Turbines Applying a Double Multiple Streamtube Model

The complex unsteady aerodynamics of vertical axis wind turbines (VAWT) poses significant challenges to the simulation tools. Dynamic stall is one of the phenomena associated with the unsteady conditions for VAWTs, and it is in the focus of the study. Two dynamic stall models are compared: the widely-used Gormont model and a Leishman–Beddoes-type model. The models are included in a double multiple streamtube model. The effects of flow curvature and flow expansion are also considered. The model results are assessed against the measured data on a Darrieus turbine with curved blades. To study the dynamic stall effects, the comparison of force coefficients between the simulations and experiments is done at low tip speed ratios. Simulations show that the Leishman–Beddoes model outperforms the Gormont model for all tested conditions.

Overview and Design of self-acting pitch control mechanism for vertical axis wind turbine using multi body simulation approach

Awareness about wind energy is constantly growing in the world. Especially a demand for small scale wind turbine is increasing and various products are available in market. There are mainly two types of wind turbines, horizontal axis wind turbine and vertical axis wind turbines. Horizontal axis wind turbines are suitable for high wind speed whereas vertical axis wind turbines operate relatively low wind speed area. Vertical axis wind turbines are cost effective and simple in construction as compared to the horizontal axis wind turbine. However, vertical axis wind turbines have inherent problem of self-start inability and has low power coefficient as compare to the horizontal axis wind turbine. These two problems can be eliminated by incorporating the blade pitching mechanism. So, in this paper overview of various pitch control systems is discussed and design of self-acting pitch mechanism is given. A pitch control linkage mechanism for vertical axis wind turbine is modeled by multi-body approach using MSC Software. Aerodynamic loads are predicted from a mathematical model based on double multiple stream tube method. An appropriate airfoil which works at low Reynolds number is selected for blade design. It is also focused on commercialization of the vertical axis wind turbine which incorporates the self-acting pitch control system. These aerodynamic load model will be coupled with the multi-body model in future work for optimization of the pitch control linkage mechanism. A 500 Watt vertical axis wind turbine is designed and it is planned to implement the self-acting pitch control mechanism in real model.

Comparison of aerodynamic models for Vertical Axis Wind Turbines

Multi-megawatt Vertical Axis Wind Turbines (VAWTs) are experiencing an increased interest for floating offshore 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 flow 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. The results show that the streamtube models are inaccurate, and that correct predictions of rotor power and rotor thrust are an effect of error cancellation which only occurs at specific configurations. The other four models, which explicitly model the wake as a system of vorticity, show mostly differences due to the instantaneous or time averaged formulation of the loading and flow, for which further research is needed.

Straight-bladed vertical axis wind turbine rotor design guide based on aerodynamic performance and loading analysis

Vertical axis wind turbines with straight blades are attractive for their relatively simple structure and aerodynamic performance. An efficient design methodology is required to enhance this resurging renewable energy technology. This paper aims to provide a robust design procedure built on an existing analytical approach to determine the optimum range of the design parameters for prototype construction. Identifying the proper range of design parameters can save significant time and resources in the initial turbine development stages. Here the double-multiple streamtube method has been utilized to analyze turbine aerodynamic performance. A parametric optimization has been performed for several design factors to maximize the turbine power coefficient and its operational range. The results show that the optimum value of the rotor solidity factor, blade aspect ratio, and rotor aspect ratio are in the range of 0.2 < σ < 0.6, 10 < μ < 20, and 0.5 < H/ D < 2, respectively. Aerodynamic loading analysis has also been carried out, and the most severe stresses acting on the blades and supporting arms were determined. The most favorable bending stress distribution along the blade occurred when two supporting arms per blade were used at intermediate locations of 21% and 79% along the blade length. A comparative study of different supporting arm shapes demonstrated that utilizing aerodynamic profiles for turbine arms created the most acceptable aerodynamic response. A summary of design aspects addressed in this paper is presented in a useful summary flowchart.

Effect of moment of inertia to H type vertical axis wind turbine aerodynamic performance

The main aerodynamic performances (out power out power coefficient torque torque coefficient and so on) of H type Vertical Axis wind Turbine (H-VAWT) which is rotating machinery will be impacted by moment of inertia. This article will use NACA0018 airfoil profile to analyze that moment of inertia through impact performance of H type VAWT by utilizing program of Matlab and theory of Double-Multiple Streamtube. The results showed that the max out power coefficient was barely impacted when moment of inertia is changed in a small area,but the lesser moment of inertia's VAWT needs a stronger wind velocity to obtain the max out power. The lesser moment of inertia's VAWT has a big out power coefficient, torque coefficient and out power before it gets to the point of max out power coefficient. Out power coefficient, torque and torque coefficient will obviously change with wind velocity increased for VAWT of the lesser moment of inertia.

Model improvements for evaluating the effect of tower tilting on the aerodynamics of a vertical axis wind turbine

ABSTRACTIf a vertical axis wind turbine is mounted offshore on a semi‐submersible, the pitch motion of the platform will dominate the static pitch and dynamic motion of the platform and wind turbine such that the effect of tower tilting on the aerodynamics of the vertical axis wind turbine should be investigated to more accurately predict the aerodynamic loads. This paper proposes certain modifications to the double multiple‐streamtube (DMS) model to include the component of wind speed parallel to the rotating shaft. The model is validated against experimental data collected on an H‐Darrieus wind turbine in skewed flow conditions. Three different dynamic stall models are also integrated into the DMS model: Gormont's model with the adaptation of Strickland, Gormont's model with the modification of Berg and the Beddoes–Leishman dynamic stall model. Both the small Sandia 17 m wind turbine and the large DeepWind 5 MW are modelled. According to the experimental data, the DMS model with the inclusion of the dynamic stall model is also well validated. On the basis of the assumption that the velocity component parallel to the rotor shaft is small in the downstream part of the rotor, the effect of tower tilting is quantified with respect to power, rotor torque, thrust force and the normal force and tangential force coefficients on the blades. Additionally, applications of Glauert momentum theory and pure axial momentum theory are compared to evaluate the effect of the velocity component parallel to the rotor shaft on the accuracy of the model. Copyright © 2013 John Wiley & Sons, Ltd.

Rotor Design and Performance Study of a Vertical-Axis Wind Turbine Based on DMS

Specifically address the design of a 5KW H-type vertical-axis wind turbine (H-VAWT) with NACA 0018 airfoil considering the factors that affect wind turbine power. The double-multiple streamtube (DMS) theoretical model is analyzed and summarized and calculated by Matlab. The 5KW H-type vertical axis wind turbines aerodynamic performance is calculated by the model written in Matlab. The curve of the power coefficient as a function of the tip-speed ratio and the curve of the normal force coefficient and the tangential farce as a function of the blade position is given by Matlab. From the curves we can see that upwind rotor aerodynamic load is larger, downwind rotor aerodynamic load is smaller and there is a serious flow retarding effect in the rotor downwind area.

Active Blade Pitch Control for Straight Bladed Darrieus Vertical Axis Wind Turbine of New Design

As Development of smallvertical axis wind turbines (VAWT) for urban use is becoming an interestingtopic both within industry and academia. However, there are few new designs ofvertical axis turbines which are customized for building integration. These aregetting importance because they operate at low rotational speed producing veryless noise during operation, although these are less efficient than HorizontalAxis Wind Turbines (HAWT). The efficiency of a VAWT has been significantlyimproved by H-Darrieus VAWT design based on double airfoil technology asdemonstrated by the authors in a previous publication. Further, it is well knowthat the variation of the blade pitch angle during the rotation improves thepower efficiency. A blade pitch variation is implemented by active blade pitchcontrol, which operates as per wind speed and position of the blade withrespect to the rotor. A double multiple stream tube method is used to determinethe performance of the H-Darrieus VAWT. The power coefficient is compared withthat of a fixed pitch and a variable pitch double airfoil blade VAWT. It isdemonstrated that an improvement in power coefficient by 20% is achieved andthe turbine could start at low wind speed

Development and Evaluation of an Aerodynamic Model for a Novel Vertical Axis Wind Turbine Concept

There has been a resurgence of interest in the development of vertical axis wind turbines which have several inherent attributes that offer some advantages for offshore operations, particularly their scalability and low over-turning moments with better accessibility to drivetrain components. This paper describes an aerodynamic performance model for vertical axis wind turbines specifically developed for the design of a novel offshore V-shaped rotor with multiple aerodynamic surfaces. The model is based on the Double-Multiple Streamtube method and includes a number of developments for alternative complex rotor shapes. The paper compares predicted results with measured field data for five different turbines with both curved and straight blades and rated powers in the range 100–500 kW. Based on these comparisons, the paper proposes modifications to the Gormont dynamic stall model that gives improved predictions of rotor power for the turbines considered.

Aerodynamic design and economical evaluation of site specific small vertical axis wind turbines

The growing demand for renewable energy with a sustainable and low-energy design is the main topic in many countries. This could indeed influence in utilizing small wind turbines which incorporate innovative designs and new materials of construction which may provide an attractive prospect of future applications of power production in the urban environment. In particular, H-rotor type vertical axis wind turbines (VAWTs) are considered as one of the most attractive solutions due to simplicity and ease of manufacturing. Optimized site-specific designs proved reductions in cost of energy by increasing in annual energy yield and a reduction in manufacturing costs. The greatest benefits were reported at sites with low mean wind speed and low turbulence. The terrain studied here is a site in Fadashk area in the province of south Khorasan in north east of Iran. The aim of this work is to design and optimize the site specific H-rotor type VAWT using the blade element momentum theory (BEM) and a double multiple stream tube model. The results of these analyses were then combined and synthesized for a 1.5kW H-rotor VAWT with NACA4415 airfoil sections. The economical feasibility of the designed VAWT is finally integrated in the design procedure to predict annual production of electricity. Based on current electricity costs that is 12cent per kWh in Iran for renewable energies, our evaluation shows a profit of 6cent per each kWh generated power by the designed VAWT.

Economical Darrieus straight bladed vertical axis wind turbine for renewable energy applications

AbstractIn remote and stand alone applications, the simple straight bladed Darrieus type vertical axis wind turbine is very practical due to its simple design and low cost of construction. It has the potential to compete effectively with the more widely used horizontal axis wind turbines. This project explores a Darrieus type vertical axis wind turbine, adapted for domestic electricity generation. Design, construction and modelling of a three-blade vertical axis wind turbine with 305 cm long blades, 55 cm chord length, which formed a symmetrical airfoil of National Advisory Committee for Aeronautics (NACA 0018) profile, was performed in this study to demonstrate how used materials can be recycled to produce an economically feasible Darrieus type vertical axis wind turbine that can be utilised to produce usable electrical power. The double multiple streamtube model was used to reproduce this turbine. Materials used were chosen for practicality, availability within the southern Caribbean islands of Trinidad...

Vertical Axis Wind Turbine Performance Prediction: An Approach to the Double Multiple Streamtube Model

The vertical axis wind turbines (VAWT) have been suffering an increased acceptance for urban wind turbines integration in the future smart grid for decentralized generation (DG). The VAWT have several advantages over the more conventional horizontal axis wind turbines (HAWT): the smaller number of components; low sound emissions; their insensitivity to fast changes in wind flow direction; a lower architectural visual impact; the ability to operate closer to the ground; and others. But, the VAWT aerodynamic performance is more complex to simulate and predict due to its three dimensional operation. Several mathematical models have been presented to predict the VAWT performance, such as the double multiple streamtube (DMS) model. With the aim of presenting a tool to ease the study of complex shaped VAWTs, being at the same time able to be easily integrated in computational design tools, a new approach to the DMS model is presented in this paper.

Gyroscopic effects on a large vertical axis wind turbine mounted on a floating structure

Abstract This paper presents an analysis technique for investigating the effects of gyroscopic couples on the behaviour of a large vertical axis wind turbine mounted on a floating semi-submersible vessel. Equations of motion in 6 degrees of freedom are formulated in the frequency domain. Time domain aerodynamic loads are derived from a double multiple stream tube model based Paraschivoiu [13] . These loads are transposed to the frequency domain and integrated with a formulation of the gyroscopic moments acting for the wind turbine rotating and the semi-submersible rotating in roll and pitch due to ocean waves. The paper uses this model to explore the effect of gyroscopic effects on the motions of the turbine and semi-submersible. It is shown that the gyroscopic effect has negligible effects on some modes of motion but that it introduces significant motions at key frequencies related to rotor speed.

A Modified Streamtube Model for Vertical Axis Wind Turbines

This work introduces a modified double-multiple streamtube model for Vertical Axis Wind Turbines (VAWT) that takes into account some parameters that were neglected till now. For example, the model considers the directions of the flow, rather than assuming that the flow is parallel to the free-wind. Also a formulation is established to calculate the effect of inclination of the blades in any direction. The modifications are facilitated by considering the momentum conservation in a direction perpendicular to the force (which was abandoned in the traditional models). The model results are compared to other models and to experimental results with a fair agreement.

S051042 バタフライ風車と四重多流管理論の提案

In this study, a new type of vertical axis wind turbine (VAWT) named as Butterfly Wind Turbine had been proposed, which has armless blades consisting of a closed curve. Since a part of flow intersects the Butterfly Wind Turbine rotor four times, a new flow-field model used in BEM (Blade-Element Momentum) theory was proposed. The model was named as Quadruple-Multiple Streamtube (QMS) model, which nests the Double-Multiple Streamtube (DMS) model. Power characteristics of three kinds of VAWTs, that is, general single-straight-blade VAWT, double-straight-blade VAWT, and Butterfly VAWT, were simulated based on the BEM theory using the QMS model. The results show that, under the condition of a constant chord length, the Butterfly Wind Turbines improve the starting performance of general VAWT as well as double-straight-blade VAWTs. Furthermore, a Butterfly VAWT equipped with tapered blades shows higher power coefficient at low rotational speed condition, without significant decrease in maximum power coefficient.