Flow Field Of Wind Turbine Research Articles

The Effect of Blade Coning on the Flow Field of Wind Turbines under Yaw Conditions

Most wind turbines operate under yaw conditions, which can reduce the output power of wind turbines. In order to improve the power of wind turbines under yaw conditions, this paper adopts a method of blade taper to study its impact on the wind turbine flow field. A 2000W wind turbine is chosen as the research object and SOILDWORKS software is employed to establish a model of blade taper. Three cone angles of 4 °, 8 °, and 12 ° were used, and numerical simulations were conducted using STARCCM+. It is found that under 30 ° yaw conditions, the blade with a cone angle of 12 ° had the highest output power, followed by 8 ° and 4 °. Compared to 4 °, the output power of 12 ° and 8 ° increased by 2.32% and 5.99%, respectively. At the same time, appropriately increasing the blade cone angle can also reduce the dissipation of tip vortices and center vortices in the flow field. By analyzing the limit streamline diagram, it can be concluded that the vorticity at an 8 ° cone angle is less than the other two cone angles under 30 ° operating conditions. Therefore, in this simulation, the comprehensive performance of the 8 ° cone angle is better, which not only improves the output power under 30 ° yaw, but also makes the operation of the wind turbine more stable.

Investigating of Flow Field and Power Performance on a Straight-blade Vertical Axis Wind Turbine with CFD Simulation

Forecasting the power performance and flow field of straight-blade vertical axis wind turbine (VAWT) and paying attention to the dynamic stall can enhance more adaptability to high turbulence and complicated wind conditions in cities environment. According to the blade element-momentum theory, the force of blade is analyzed in one period of revolution based on the structural characteristics of straight blade airfoil. The power performance of VAWT obtained by computational fluid dynamics (CFD) simulation is compared with experiment to estimate the accuracy about the numerical simulation results. As a result, the trend of average value of simulation Cpower is entirely consistent with the value of experiment data, and the extreme value of average Cpower of VAWT is 0.225 for tip speed ration (TSR) λ=2.19 when the freestream velocity is 8 m/s. The flow separation around the blade surface also gradually changes with the azimuth angle increasing, and the maximum pressure difference on the blade surface appears in the upstream. In the case of high leaf tip velocity, the synthetic velocity is much larger than the incoming wind velocity, and the angle of synthetic velocity increases slightly with the increase of blade tangential velocity. Thus, the angles of attack are very close in two TSRs λ=2.19 and 2.58. The research provides a computational model and theoretical basis for predicting wind turbine flow field to improve wind turbine power performance.

Stochastic assessment of aerodynamics within offshore wind farms based on machine-learning

Abstract Wind turbine flow field prediction is difficult as it requires computationally expensive computational fluid dynamics (CFD) models. The contribution of this paper is to propose and develop a method for stochastic analysis of an offshore wind farm using CFD and a non-intrusive stochastic expansion. The approach is developed through testing a range of machine-learning methods, evaluating dataset requirements and comparing the accuracy against site measurement data. The approach used is detailed and the results are compared with real measurements obtained from the existing wind farm to quantify the accuracy of the predictions. An existing offshore wind farm is modelled using a steady-state CFD solver at several deterministic input ranges and an approximation model is trained on the CFD results. The approximation models compared are Artificial Neural Networks, Gaussian Process, Radial Basis Function, Random Forest and Support Vector Regression. RBF achieves a mean absolute error relative to the CFD model of only 0.54% and the error of the SVR predictions relative to the real data, with scatter, was 12%, compared to 16% from Jensen. This approach has the potential to be used in more complex situations where an existing analytical method is either insufficient or unable to make a good prediction.

Numerical Simulation and Modal Analysis of External Flow Field of Large Wind Turbine

Aiming at the problems of complex and slow optimization process of large-scale wind turbine blade design and the influence of wind turbine flutter, etc. The numerical simulation analysis and modal analysis of the external flow field of the wind turbine under the rated wind speed are carried out by the hybrid method. A fluid simulation model based on CFD was established. The method of rotating reference frame and SST k-omega turbulence model are used to simulate the external flow of fan wind turbine in FLUENT. The first 6 natural modes of the wind wheel are calculated in Hypermesh/Optistruct. The results show that the hybrid simulation method can quickly obtain the impeller flow field information, and the flow of the tip portion is extremely unstable. In each natural mode, the blade deformation position is basically from the maximum chord length to the tip position. The closer to the tip, the more obvious the blade vibration deformation is. At the same time, the first-order natural frequency of the wind wheel is 0.919Hz, which is greater than 0.382Hz when the rated speed is 12m/s, thus effectively avoiding resonance phenomenon.

A new wind turbine icing computational model based on Free Wake Lifting Line Model and Finite Area Method

Based on the Free Wake Lifting Line (FWL) Model and Finite Area Method (FAM), a new wind turbine icing computational model, named FFICE, is developed in this paper. By utilizing the fast calculation characteristics of the FWL model, the 3D flow field of wind turbine can be computed. According to the results, the 3D icing problem is transformed into different 2D conditions along the span of the blade. Then, the Lagrangian Method is applied to calculate the collection efficiency on the surface of the local airfoil. In order to accurately simulate the ice accretion, the heat and mass transfer process in the water film is solved by the modified FAM numerical computational method. All the modules involved in FFICE model is validated according to the numerical or experimental results. After that, the dynamic characters of the water film during the icing process on NACA 0012 airfoil is analyzed. At last the icing analysis of NREL Phase VI wind turbine is performed and the results are discussed in detail. The FFICE model provides an effective way for wind turbine icing analysis, which could be easily incorporated into the Icing Protection System (IPS) design code.

Evolution of turbulence in a wind turbine flow field with a neutral atmospheric boundary layer and an analysis of the blade root load

In this study, a neutral atmospheric boundary layer and wind turbine blades were constructed in a large eddy simulation and actuator line model for conducting a field experiment of a wind turbine. Further, the flow field of the wind turbine was simulated in a neutral atmospheric boundary layer. The evolution of the turbulence in the front and back of the rotor with a neutral atmospheric boundary layer and its correlation with the load were studied by analyzing the continuous wavelets, the spectrum, and the correlation. The results indicate that the coherent structure of the turbulence in the neutral atmospheric boundary layer becomes stronger from one-diameter (1 D ) front of the rotor plane to 1 D back of it. The coherent structure of the turbulence in inflow is affected by the rotation of the rotor. Subsequently, strong small-scale turbulence structures appear in the rotor plane, which are continuously dissipated in the wind direction. The turbulent energy with small scales at 1 D back of rotor is feeble, and the turbulence mainly moves on a large scale. The frequency of the small-scale turbulence is approximately 1.82 Hz at the tip, which corresponds to the passing frequency of the blade and is mainly generated because of the rotation of the rotor. The flapwise load of the blade root is high when the turbulent energy is high. The results of wavelet analysis denote that the turbulence structure at the monitoring points has a good relation with the flapwise load of the blade root, and the flapwise load of the blade root of the wind turbine has obvious response to the turbulent structure of the atmosphere. A multi-resolution analysis of two points at the center and tip of the rotor and the flapwise load of the blade root denotes that the low-frequency turbulent structure at the center of the rotor (B3–B6 frequency band) is dependent on the low-frequency flapwise load of the blade root, whereas the high-frequency turbulent structure (B1–B2 frequency band) has no obvious corresponding relation with the flapwise load of the blade root. The high-frequency turbulent structure at the tip (B1–B2 frequency band) is related to the high-frequency flapwise load of the blade root, whereas the low-frequency turbulent structure (B3–B6 frequency band) has no obvious corresponding relation with the flapwise load of the blade root. Therefore, the low-frequency turbulence structure significantly influences the low-frequency band of the flapwise load of the blade root, whereas the high-frequency turbulence structure significantly influences the high-frequency band of the flapwise load of the blade root. When compared with the high-frequency turbulent structure at the blade root, the high-frequency turbulent structure has a higher frequency and a higher energy at the blade tip, and its influence on the high-frequency band of the flapwise load of the blade root is more obvious, exhibiting a consistent regular periodic variation.

Determination of pitch angles and wind speeds ranges to improve wind turbine performance when using blade tip plates

In this article a wind turbine performance enhancement is studied numerically using two type of tip plates. A three dimensional finite volume code is developed to simulate the wind turbine flow field periodically at different wind speeds and pitch angles. The well-known Menter's Shear Stress Transport (kω−SST) turbulence modelling is incorporated into the code to investigate the turbulent flow field that occurs in wind turbines. Here we show that using tip plates for wind turbines performance improvement can only occur if the turbine blade pitch angle is set at the maximum output power based on the given wind speed. Otherwise, using the tip plates play negative role and reduce the wind turbine output power. This physical effect is related to the wind turbine working condition at which both the blade span-wise flow as well as the tip blade trailing vortices stay at their minimum amount.

Establishing a fully coupled CFD analysis tool for floating offshore wind turbines

An accurate study of a floating offshore wind turbine (FOWT) system requires interdisciplinary knowledge about wind turbine aerodynamics, floating platform hydrodynamics and mooring line dynamics, as well as interaction between these discipline areas. Computational Fluid Dynamics (CFD) provides a new means of analysing a fully coupled fluid-structure interaction (FSI) system in a detailed manner. In this paper, a numerical tool based on the open source CFD toolbox OpenFOAM for application to FOWTs will be described. Various benchmark cases are first modelled to demonstrate the capability of the tool. The OC4 DeepCWind semi-submersible FOWT model is then investigated under different operating conditions.With this tool, the effects of the dynamic motions of the floating platform on the wind turbine aerodynamic performance and the impact of the wind turbine aerodynamics on the behaviour of the floating platform and on the mooring system responses are examined. The present results provide quantitative information of three-dimensional FSI that may complement related experimental studies. In addition, CFD modelling enables the detailed quantitative analysis of the wind turbine flow field, the pressure distribution along blades and their effects on the wind turbine aerodynamics and the hydrodynamics of the floating structure, which is difficult to carry out experimentally.

Newton's Method of Wind Turbine Flow Field Numerical Simulation of Local Convergence Analysis

Newton's Method of Wind Turbine Flow Field Numerical Simulation of Local Convergence Analysis

Wind loads and load-effects of large scale wind turbine tower with different halt positions of blade

In order to investigate the influence of different blade positions on aerodynamic load and wind loads and load-effects of large scale wind turbine tower under the halt state, we take a certain 3 MW large scale horizontal axis three-blade wind turbine as the example for analysis. First of all, numerical simulation was conducted for wind turbine flow field and aerodynamic characteristics under different halt states (8 calculating conditions in total) based on LES (large eddy simulation) method. The influence of different halt states on the average and fluctuating wind pressure coefficients of turbine tower surface, total lift force and resistance coefficient, circular flow and wake flow characteristics was compared and analysed. Then on this basis, the time-domain analysis of wind loads and load-effects was performed for the wind turbine tower structure under different halt states by making use of the finite element method. The main conclusions of this paper are as follows: The halt positions of wind blade could have a big impact on tower circular flow and aerodynamic distribution, in which Condition 5 is the most unfavourable while Condition 1 is the most beneficial condition. The wind loads and load-effects of disturbed region of tower is obviously affected by different halt positions of wind blades, especially the large fluctuating displacement mean square deviation at both windward and leeward sides, among which the maximum response occurs in <TEX>$350^{\circ}$</TEX> to the tower top under Condition 8; the maximum bending moment of tower bottom occurs in <TEX>$330^{\circ}$</TEX> under Condition 2. The extreme displacement of blade top all exceeds 2.5 m under Condition 5, and the maximum value of windward displacement response for the tip of Blade 3 under Condition 8 could reach 3.35 m. All these results indicate that the influence of halt positions of different blades should be taken into consideration carefully when making wind-resistance design for large scale wind turbine tower.

Analysis and Evaluation of Wind Turbine Flow Field and Noise Simulation Based on CFD Software

CFD is the abbreviation of the computational fluid dynamics, which is widely used in engineering fluid simulation. Based on two-dimensional N-S equation and k-e turbulence model, this paper uses FLUENT software, finite volume method and SIMPLEC algorithm to do numerical simulation and analysis on flow field in centrifugal fan. In order to improve the efficiency and accuracy of calculation, this paper uses AutoCAD to establish the two-dimensional model of fan, and uses the structured triangular mesh to divide grid. Encrypting the blade can improve the precision and also save the computer memory. Through the calculation we get the internal flow field velocity and pressure distribution in the wind turbine, and get the power level cloud of internal noise in fan. It provides the technical reference for the optimization design of wind turbine.