scholarly journals Wind Tunnel Test on the Effect of Solidity on Near Wake Instability of Vertical-Axis Wind Turbine

2020 ◽  
Vol 8 (5) ◽  
pp. 365
Author(s):  
Li Zou ◽  
Kun Wang ◽  
Yichen Jiang ◽  
Aimin Wang ◽  
Tiezhi Sun
Keyword(s):  
Vortex Shedding ◽  
Large Scale ◽  
Bluff Body ◽  
Low Frequency ◽  
Vertical Axis ◽  
Vertical Axis Wind Turbine ◽  
Near Wake ◽  
Wake Instability ◽  
Large Scale Vortex ◽  
Bluff Body Wake

Owing to the rapid development of the offshore wind power technology and increasing capacity of wind turbines, vertical-axis wind turbines (VAWTs) have experienced a great development. Nevertheless, the VAWT wake effect, which affects the power generation efficiency and rotor fatigue life, has not been thoroughly understood. In this study, the mid-span wake measurements on a VAWT in six different configurations were conducted. This study aimed to investigate the effect of solidity on near wake instability of vertical-axis wind turbine. By using the wavelet analysis method to analyse the measured velocity (or pressure) time series signals on a multi-scale and with multi-resolution, the dynamic characteristics of the coherent vortex structures in the wake evolution process were determined. The results show that with increasing solidity, the VAWT wake develops into a bluff body wake mode. In addition, a characteristic frequency that is lower than the low-frequency large-scale vortex shedding frequency occur. The wavelet transform was used to decompose and reconstruct the measured data, and the relationship between the low-frequency large-scale vortex shedding and lower frequency pulsation was established. The results provide important data for numerical modelling and new insights into the physical mechanism of the VAWT wake evolution into a bluff body wake.

Transition to bluff-body dynamics in the wake of vertical-axis wind turbines

2017 ◽  
Vol 813 ◽  
pp. 346-381 ◽  
Author(s):  
Daniel B. Araya ◽  
Tim Colonius ◽  
John O. Dabiri
Keyword(s):  
Velocity Field ◽  
Circular Cylinder ◽  
Large Scale ◽  
Wind Farm ◽  
Bluff Body ◽  
Vertical Axis ◽  
Speed Ratio ◽  
Cylinder Wake ◽  
Vertical Axis Wind Turbine ◽  
Far Wake

We present experimental data to demonstrate that the far wake of a vertical-axis wind turbine (VAWT) exhibits features that are quantitatively similar to that of a circular cylinder with the same aspect ratio. For a fixed Reynolds number ($Re\approx 0.8\times 10^{5}$) and variable tip-speed ratio, two-dimensional particle image velocimetry (PIV) is used to measure the velocity field in the wake of four different laboratory-scale models: a 2-bladed, 3-bladed and 5-bladed VAWT, as well as a circular cylinder. With these measurements, we use spectral analysis and proper orthogonal decomposition (POD) to evaluate statistics of the velocity field and investigate the large-scale coherent motions of the wake. In all cases, we observe three distinct regions in the VAWT wake: (i) the near wake, where periodic blade vortex shedding dominates; (ii) a transition region, where growth of a shear-layer instability occurs; (iii) the far wake, where bluff-body wake oscillations dominate. We define a dynamic solidity parameter, $\unicode[STIX]{x1D70E}_{D}$, that relates the characteristic scales of the flow to the streamwise transition location in the wake. In general, we find that increasing $\unicode[STIX]{x1D70E}_{D}$ leads to an earlier transition, a greater initial velocity deficit and a faster rate of recovery in the wake. We propose a coordinate transformation using $\unicode[STIX]{x1D70E}_{D}$ in which the minimum velocity recovery profiles of the VAWT wake closely match that of the cylinder wake. The results have implications for manipulating VAWT wake recovery within a wind farm.

The effect of angular misalignment on low-frequency axisymmetric wake instability

2017 ◽  
Vol 813 ◽  
Author(s):  
V. Gentile ◽  
B. W. van Oudheusden ◽  
F. F. J. Schrijer ◽  
F. Scarano
Keyword(s):  
Reynolds Number ◽  
Boundary Conditions ◽  
Large Scale ◽  
Low Frequency ◽  
Axisymmetric Body ◽  
Angular Range ◽  
Reversed Flow ◽  
Near Wake ◽  
Angular Misalignment ◽  
Wake Instability

The effect of angular misalignment on the low-frequency dynamics of the near wake of a blunt-based axisymmetric body is investigated at a Reynolds number of $Re=67\,000$. While for axisymmetric boundary conditions all azimuthal orientations of the wake are explored with equal probability, resulting in a statistical axisymmetry, an angular offset as small as $0.2^{\circ }$ is found to suppress the low-frequency large-scale behaviour that is associated with the erratic meandering of the region of reversed flow. As a result of the misalignment, the centroid of this backflow region is displaced from the model axis and remains confined around an average off-centre position. Spectral and modal analysis provides evidence that the erratic backflow behaviour occurs within a narrow angular range of deviations from axisymmetric conditions.

scholarly journals Dynamic responses of anchored ducted flames to harmonic velocity forcing

2017 ◽  
Vol 10 (1) ◽  
pp. 72-85
Author(s):  
Ze-tian Ren ◽  
Su-hui Li ◽  
Min Zhu
Keyword(s):  
Large Scale ◽  
Bluff Body ◽  
Flow Instability ◽  
Low Frequency ◽  
Vortex Method ◽  
Vortex Structures ◽  
Dynamic Responses ◽  
Discrete Vortex ◽  
Flame Response ◽  
Complicated Geometries

This paper aims at developing a computationally inexpensive method to investigate the premixed flame instabilities. The kinematic G-equation is combined with a two-dimensional discrete vortex method, and the conformal mapping is applied to make calculations for complicated geometries more efficiently. The vortex dynamics and flame response to harmonic velocity forcing of an anchored ducted V-flame are investigated, and the effects of harmonic forcing, Reynolds number, and bluff body geometry are examined. Results show that the vortex structures, flow instability, and flame response are closely coupled with each other. The unsteady vortex structures generate instabilities at the flame base, and the convection of the flame wrinkles then influences the flame dynamics downstream. The flame heat release fluctuates with larger amplitude under low-frequency forcings, while the phase of the flame transfer function is quasi-linear with increasing forcing frequency. Both higher inflow velocity and sharper bluff body corners can result in more unsteady large-scale vortex structures and hence influence the flame responses.

Study on vortex shedding mode on the wake of horn/ridge ice contamination under high-Reynolds conditions

2019 ◽  
Vol 233 (13) ◽  
pp. 5045-5056
Author(s):  
Shufan Hu ◽  
Chen Zhang ◽  
Hong Liu ◽  
Fuxin Wang
Keyword(s):  
Proper Orthogonal Decomposition ◽  
Vortex Shedding ◽  
Large Scale ◽  
Vortex Motion ◽  
Simulation Method ◽  
Orthogonal Decomposition ◽  
Detached Eddy Simulation ◽  
Dynamic Features ◽  
Large Scale Vortex ◽  
Proper Orthogonal

This paper studied the unsteadiness of vortex motion produced by a three-dimensional wing section with horn/ridge ice contamination. Using improved delayed detached eddy simulation method, multi-scale vortex and their associated flow structures were successfully captured. Results have shown a diversity of unsteadiness scales at different time series, including shear layer instability, vortex pairing, co-rotating and breaking up. Proper orthogonal decomposition was then introduced to extract the characteristic vortex shedding modes with scheduling the eigenvalues λi from large to small. The dominate and secondary proper orthogonal decomposition modes under horn ice condition were displayed, which could be illustrated as fluctuations near recirculation zone, and large-scale vortex shedding/reattaching motion, respectively. The proper orthogonal decomposition modal characteristics for ridge ice showed that vortex scales varied from large to small. The trajectory of large-scale vortex reattaching and co-rotating exist simultaneously with the pressure peak and recover, which also verified the association of proper orthogonal decomposition modes with different scales of vortices. Future works would be presented on demonstration of the complex structures and the dynamic features in such flow.

Control of vortex shedding in an axisymmetric bluff body wake

2000 ◽  
Vol 19 (5) ◽  
pp. 789-812 ◽  
Author(s):  
Ansgar Weickgenannt ◽  
Peter A. Monkewitz
Keyword(s):  
Vortex Shedding ◽  
Bluff Body ◽  
Bluff Body Wake

scholarly journals Stochastic modelling and feedback control of bistability in a turbulent bluff body wake

2016 ◽  
Vol 802 ◽  
pp. 726-749 ◽  
Author(s):  
R. D. Brackston ◽  
J. M. García de la Cruz ◽  
A. Wynn ◽  
G. Rigas ◽  
J. F. Morrison
Keyword(s):  
Reynolds Number ◽  
Feedback Control ◽  
Symmetry Breaking ◽  
Large Scale ◽  
Bluff Body ◽  
Three Dimensional ◽  
Power Saving ◽  
Stochastic Modelling ◽  
Bluff Body Wake ◽  
Modelling Approach

A specific feature of three-dimensional bluff body wakes, flow bistability, is a subject of particular recent interest. This feature consists of a random flipping of the wake between two asymmetric configurations and is believed to contribute to the pressure drag of many bluff bodies. In this study we apply the modelling approach recently suggested for axisymmetric bodies by Rigaset al.(J. Fluid Mech., vol. 778, 2015, R2) to the reflectional symmetry-breaking modes of a rectilinear bluff body wake. We demonstrate the validity of the model and its Reynolds number independence through time-resolved base pressure measurements of the natural wake. Further, oscillating flaps are used to investigate the dynamics and time scales of the instability associated with the flipping process, demonstrating that they are largely independent of Reynolds number. The modelling approach is then used to design a feedback controller that uses the flaps to suppress the symmetry-breaking modes. The controller is successful, leading to a suppression of the bistability of the wake, with concomitant reductions in both lateral and streamwise forces. Importantly, the controller is found to be efficient, the actuator requiring only 24 % of the aerodynamic power saving. The controller therefore provides a key demonstration of efficient feedback control used to reduce the drag of a high-Reynolds-number three-dimensional bluff body. Furthermore, the results suggest that suppression of large-scale structures is a fundamentally efficient approach for bluff body drag reduction.

Development of a high-efficiency and long-life 500W class H-Darrieus-type vertical axis wind turbine (VAWT) system using skin-spar-foam sandwich composite structure

2013 ◽  
Vol 20 (4) ◽  
pp. 383-394
Author(s):  
Changduk Kong ◽  
Haseung Lee
Keyword(s):  
Wind Turbine ◽  
Large Scale ◽  
High Efficiency ◽  
Vertical Axis ◽  
Small Scale ◽  
Test Results ◽  
Vertical Axis Wind Turbine ◽  
Horizontal Axis Wind Turbine ◽  
Structural Test ◽  
The City

AbstractSince the focus on the energy crisis and environmental issues due to excessive fossil fuel consumption, wind power has been considered as an important renewable energy source. Recently, several megawatt-class large-scale wind turbine systems have been developed in some countries. Even though the large-scale wind turbine can effectively produce electrical power, the small-scale wind turbine has been continuously developed due to some advantages; for instance, it can be easily built at a low cost without any limitation of location, i.e., even in the city. In case of small-scale wind turbines, the vertical axis wind turbine (VAWT) is used in the city despite having a lower efficiency than the horizontal axis wind turbine. Furthermore, most small-scale wind turbine systems have been designed at the rated wind speed of around 12 m/s. This aim of this work is to design a high-efficiency 500W class composite VAWT blade that is applicable to relatively low-speed regions. With regard to the aerodynamic design of the blade, parametric studies are carried out to decide an optimal aerodynamic configuration. The aerodynamic efficiency and performance of the designed VAWT is confirmed by computational fluid dynamics analysis. The structural design is performed by the load case study, initial sizing using the netting rule and the rule of mixture, structural analysis using finite element method (FEM), fatigue life estimation and structural test. The prototype blade is manufactured by hand lay-up and the matched die molding. The experimental structural test results are compared with the FEM analysis results. Finally, to evaluate the prototype VAWT including designed blades, the performance test is performed using a truck to simulate various ranges of wind speeds and some measuring equipment. According to the performance evaluation result, the estimated performance agrees well with the experimental test results in all operating ranges.

scholarly journals Design and Analysis of A Vortex Induced Vibration Based Oscillating Free Stream Energy Converter

2021 ◽  
pp. 112-117
Author(s):  
Ratan Kumar Das ◽  
Muhammad Taharat Galib
Keyword(s):  
Vortex Shedding ◽  
Large Scale ◽  
Bluff Body ◽  
Free Stream ◽  
Theoretical Formula ◽  
Pendulum Motion ◽  
Ansys Fluent ◽  
Vortex Induced Vibration ◽  
Karman Vortex ◽  
Lock In

The Kármán Vortex Shedding is one of the special types of vortex that is generated from asymmetric flow separation. For many years engineers tried to suppress the vortex shedding as it brings unnecessary motion to the static members inside the flow field. A converter model is designed and studied to harness the energy associated with this vortex shedding and convert it into usable form rather than suppressing it. It is a bluff body placed on the free stream incurring vortex-induced vibration and giving out a swinging pendulum motion. This motion is utilized to produce electricity. The model is analyzed on the free stream of water and conversion efficiency of 8.9% is achieved. A theoretical formula is derived regarding the force acting on the bluff body during the motion. Various parameters such as aspect ratio, flow velocity, lock-in delay, frequency of oscillation, etc. as well as their relations are studied by simulating the model in ANSYS FLUENT 18.1 for different configurations. From the simulated results it is obvious that as the lift force on the bluff body increases, more power generation is possible. Also, the experimental results paved the way for further study for practical large-scale implementation of the converter.

Development of a CFD Methodology to Reproduce the Effects of Macro Turbulence on Wind Turbines and its Application to the Particular Case of a VAWT

2019 ◽  
Author(s):  
Francesco Balduzzi ◽  
Marco Zini ◽  
Giovanni Ferrara ◽  
Alessandro Bianchini
Keyword(s):  
Wind Tunnel ◽  
Wind Turbines ◽  
Large Scale ◽  
Maximum Level ◽  
Vertical Axis ◽  
Navier Stokes ◽  
Energy Yield ◽  
Vertical Axis Wind Turbine ◽  
Energy Applications ◽  
Wind Tunnel Data

Abstract Based on existing reports and databases, most of the installations in highly turbulent sites in fact fail to reach the expected energy yield, resulting in still or underperforming turbines that also give bad press for the technology. A better understanding of the real performance of wind turbines under highly turbulent conditions is then pivotal to ensure the economic viability of new installations. To this end, the possible use of Computational Fluid Dynamics (CFD) techniques could provide notable benefits, reducing the time-to-market and the cost with respect to experiments. On the other hand, it is intrinsically not easy to reproduce properly intense and large-scale turbulence with the techniques of common use for research and industry (e.g. CFD unsteady RANS), while the only methods that are granted to do so (e.g. DNS or LES) are often not computationally affordable. Moving from this background, this study presents the development a numerical strategy to exploit at their maximum level the capabilities of an unsteady Reynolds-Averaged Navier-Stokes (RANS) approach in order to reproduce fields of macro turbulence of use for wind energy applications. The study is made of two main parts. In the first part, the numerical methodology is discussed and assessed based on real wind tunnel data. The benefits and drawbacks are presented also in comparison to other existing methods. In the second part, it has been used to simulate the behavior under turbulence of a H-Darrieus vertical-axis wind turbine, for which unique wind tunnel data were available. The simulations, even if preliminary, showed good matching with experiments (e.g. confirming the increase of power), showing then the potential of the method.

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