Assessment of wind field generation methods on predicted wind-turbine power production using a free vortex filament wake approach

2021 ◽  
pp. 1-15
Author(s):  
Hamidreza Abedi ◽  
Bastian Nebenführ ◽  
Lars Davidson
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Wind Turbine ◽  
Wind Field ◽  
Power Production ◽  
Rotor Blades ◽  
Low Frequencies ◽  
The Mean ◽  
The Impact ◽  
Simulation Time

Abstract The generated power and thrust of a wind turbine strongly depend on the flow field around the turbine. In the present study, three different inflow methods, i.e., a time series (TS) from Large-Eddy Simulation (LES) of atmospheric boundary layer flow field, a synthetic turbulent flow field using the Mann model (MM) and a steady-state mean wind profile with shear (PL), are integrated with the free vortex filament wake method to investigate the effect of wind field generation methods on the wind turbine performance where the impact of the turbine and the trailing wake vortices on the turbulent flow fields are ignored. For this purpose, an in-house Vortex Lattice Free Wake (VLFW) code is developed and used to predict the aerodynamic loads on rotor blades. The NREL 5-MW reference wind turbine is used for the VLFW simulations. For a fair assessment of different inflow generation methods on power production of a wind turbine, it is not sufficient that the generated wind fields employed in the TS and MM methods, have the same streamwise mean velocity and turbulence intensity at hub height. Instead, the generated inflows must have equivalent power-spectral densities especially at low frequencies since the rotor blades essentially respond to the large-scale fluctuations (macroscopic scales) rather than small-scale fluctuations (microscopic scales). A faster energy decay rate of LES inflow leads to a higher en-ergy content in the TS method at low frequencies (associated with the macroscopic dynamics of the rotor blades). This extra kinetic energy results in a slightly higher mean power production while using the TS method although the inflow conditions at hub height/rotor plane are the same for both the TS and MM methods. Moreover, the impact of simulation time (the length of time integration) on the power production of a wind turbine (exposed to an unsteady inflow) must be taken into account. A short simulation time remarkably affects the mean wind speed over the rotor area for identical turbulent inflows. For Taylor’s hypothesis application using a single LES flow field, the results show a significant difference in the mean powers corresponding to the different realizations due to large turbulent fluctuations.

The Impact of Manufacturing Variations on Performance of a Transonic Axial Compressor Rotor

2018 ◽  
Author(s):  
Marcus Lejon ◽  
Niklas Andersson ◽  
Lars Ellbrant ◽  
Hans Mårtensson
Keyword(s):  
Flow Field ◽  
Geometric Mean ◽  
Pressure Ratio ◽  
Axial Compressor ◽  
Mean Deviation ◽  
Design Intent ◽  
Compressor Rotor ◽  
Measuring Machine ◽  
The Mean ◽  
The Impact

In this paper, the impact of manufacturing variations on performance of an axial compressor rotor are evaluated at design rotational speed. The geometric variations from the design intent were obtained from an optical coordinate measuring machine and used to evaluate the impact of manufacturing variations on performance and the flow field in the rotor. The complete blisk is simulated using 3D CFD calculations, allowing for a detailed analysis of the impact of geometric variations on the flow. It is shown that the mean shift of the geometry from the design intent is responsible for the majority of the change in performance in terms of mass flow and total pressure ratio for this specific blisk. In terms of polytropic efficiency, the measured geometric scatter is shown to have a higher influence than the geometric mean deviation. The geometric scatter around the mean is shown to impact the pressure distribution along the leading edge and the shock position. Furthermore, a blisk is analyzed with one blade deviating substantially from the design intent, denoted as blade 0. It is shown that the impact of blade 0 on the flow is largely limited to the blade passages that it is directly a part of. The results presented in this paper also show that the impact of this blade on the flow field can be represented by a simulation including 3 blade passages. In terms of loss, using 5 blade passages is shown to give a close estimate for the relative change in loss for blade 0 and neighboring blades.

Coupled Dynamics of a Vertical Axis Wind Turbine (VAWT) With Active Blade Pitch Control on a Semi-Submersible Floater

2018 ◽  
Author(s):  
Ebert Vlasveld ◽  
Fons Huijs ◽  
Feike Savenije ◽  
Benoît Paillard
Keyword(s):  
Wind Turbine ◽  
Wind Velocity ◽  
Vertical Axis ◽  
Power Production ◽  
Mooring Line ◽  
Vertical Axis Wind Turbine ◽  
Coupled Dynamics ◽  
Low Frequencies ◽  
Pitch Control ◽  
Thrust And Torque

A vertical axis wind turbine (VAWT) typically has a low position of the center of gravity and a large allowable tilt angle, which could allow for a relatively small floating support structure. Normally however, the drawback of large loads on the VAWT rotor during parked survival conditions limits the extent to which the floater size can be reduced. If active blade pitch control is applied to the VAWT, this drawback can be mitigated and the benefits can be fully utilized. The coupled dynamics of a 6 MW VAWT with active blade pitch control supported by a GustoMSC Tri-Floater semi-submersible floater have been simulated using coupled aero-hydro-servo-elastic software. The applied blade pitch control during power production results in a steady-state thrust curve which is more comparable to a HAWT, with the maximum thrust occurring at rated wind velocity. During power production, floater motions occur predominantly at low frequencies. These low frequency motions are caused by variations in the wind velocity and consequently the rotor thrust and torque. For the parked survival condition, it is illustrated that active blade pitch control can be used to effectively reduce dynamic load variations on the rotor and minimize floater motions and mooring line tensions.

scholarly journals A Study of the Impact of Pitch Misalignment on Wind Turbine Performance

Machines ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 8 ◽  
Author(s):  
Davide Astolfi
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Power Output ◽  
Wind Farm ◽  
Reactive Power ◽  
Power Production ◽  
Test Case ◽  
Before And After ◽  
Input Variables ◽  
The Impact

Pitch angle control is the most common means of adjusting the torque of wind turbines. The verification of its correct function and the optimization of its control are therefore very important for improving the efficiency of wind kinetic energy conversion. On these grounds, this work is devoted to studying the impact of pitch misalignment on wind turbine power production. A test case wind farm sited onshore, featuring five multi-megawatt wind turbines, was studied. On one wind turbine on the farm, a maximum pitch imbalance between the blades of 4.5 ° was detected; therefore, there was an intervention for recalibration. Operational data were available for assessing production improvement after the intervention. Due to the non-stationary conditions to which wind turbines are subjected, this is generally a non-trivial problem. In this work, a general method was formulated for studying this kind of problem: it is based on the study, before and after the upgrade, of the residuals between the measured power output and a reliable model of the power output itself. A careful formulation of the model is therefore crucial: in this work, an automatic feature selection algorithm based on stepwise multivariate regression was adopted, and it allows identification of the most meaningful input variables for a multivariate linear model whose target is the power of the wind turbine whose pitch has been recalibrated. This method can be useful, in general, for the study of wind turbine power upgrades, which have been recently spreading in the wind energy industry, and for the monitoring of wind turbine performances. For the test case of interest, the power of the recalibrated wind turbine is modeled as a linear function of the active and reactive power of the nearby wind turbines, and it is estimated that, after the intervention, the pitch recalibration provided a 5.5% improvement in the power production below rated power. Wind turbine practitioners, in general, should pay considerable attention to the pitch imbalance, because it increases loads and affects the residue lifetime; in particular, the results of this study indicate that severe pitch misalignment can heavily impact power production.

Turbulence Measurements in the Corner Wall Jet

2014 ◽  
Author(s):  
Barrett Poole ◽  
Joseph W. Hall
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Turbulent Flow ◽  
Three Dimensional ◽  
Wall Jet ◽  
Hot Wire ◽  
Turbulence Measurements ◽  
Vertical Growth ◽  
The Mean ◽  
Turbulent Flow Field

The corner wall jet is similar to the standard three-dimensional wall jet with the exception that one half of the surface has been rotated counter-clockwise by 90 degrees. The corner wall jet investigated here is formed using a long round pipe with a Reynolds number of 159,000. Contours of the mean and turbulent flow field were measured using hot-wire anemometry. The results indicate that the ratio of lateral to vertical growth in the corner wall jet is approximately half of that in a standard turbulent three-dimensional wall jet.

Investigation of Fan Rotor Interaction With Pressure Disturbance Produced by Downstream Pylon

2013 ◽  
Author(s):  
Tomonori Enoki ◽  
Hidekazu Kodama ◽  
Shinya Kusuda
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Numerical Results ◽  
Rotor Blades ◽  
Flow Structures ◽  
Coupled Analysis ◽  
Unsteady Forces ◽  
Rotor Stator Interaction ◽  
The Impact ◽  
Potential Pressure

This paper presents an investigation of fan rotor interaction with potential pressure disturbances produced by a downstream pylon. Three-dimensional unsteady viscous analyses are performed for two fan rotor-stator-pylon configurations with different axial gaps between the stator and the pylon, and compared with the experimental results. To clarify the impact of the rotor-pylon interaction on the potential pressure flow field, a numerical analysis for the configuration in which a fan rotor is removed is also performed and compared with the numerical results with fan rotor. Actuator disk analyses are also performed to interpret the flow structures observed in the experiments and the numerical results. It is found that a fan rotor-stator interaction also exists in the fan flow field, and this may impact on the upstream propagating potential flow that dominates the unsteady forces acting on the rotor blades. A coupled analysis between fan rotor and stator is essential to accurately predict the unsteady blade force.

Aerodynamic Performance Investigation under the Influence of Heavy Rain of a NACA 0012 Airfoil for Wind Turbine Applications

2012 ◽  
Vol 6 (6) ◽  
pp. 1228-1235
Author(s):  
Eleni C. Douvi ◽  
Dionissios P. Margaris
Keyword(s):  
Flow Field ◽  
Wind Turbine ◽  
Heavy Rain ◽  
Aerodynamic Characteristics ◽  
Aerodynamic Performance ◽  
Spherical Particles ◽  
Discrete Phase Model ◽  
Two Phase ◽  
Naca0012 Airfoil ◽  
The Impact

The study of the prediction of the flow field and aerodynamic characteristics of a NACA0012 airfoil in simulated heavy rain, using a computational fluid dynamics code is presented. The simulation of rain is accomplished by using the two-phase flow Discrete Phase Model, which is available in the CFD code. Spherical particles are tracked through the two-dimensional, incompressible air flow field over a NACA0012 airfoil, at a simulated rain rate of 1000 mm/h and operating at Reynolds numbers Re=1×106 and Re=3×106. To validate the CFD developed model, the results are compared with well-established and published experimental data, showing good agreement. The aim of the work was to show the behavior of the airfoil at these conditions and to establish a verified solution method. Lift and drag coefficients are computed at various angles of attack in both dry and wet conditions and the results are compared to show the effects of rain at airfoil performance. The impact of rain on wind turbine performance is also analyzed. It is concluded that rain causes degradation of aerodynamic performance, especially lift is decreased and drag is increased.

Analysis and Evaluation of the Impact of Different Blade Loadings on a 2-Stage Turbine With Shrouded Blades

2011 ◽  
Author(s):  
Dieter Bohn ◽  
Stephan Schwab ◽  
Michael Sell
Keyword(s):  
Flow Field ◽  
Gas Turbines ◽  
Labyrinth Seal ◽  
Rotor Blades ◽  
Analysis And Evaluation ◽  
Passage Vortex ◽  
Flow Phenomena ◽  
Two Stages ◽  
Shrouded Rotor ◽  
The Impact

An important goal in the development of turbine bladings is to increase the efficiency in order to achieve an optimized use of energy resources. For that purpose a detailed understanding of flow phenomena is required. This paper presents an experimental investigation of the impact of varying blade loadings on the flow field and leakage flow. The investigations were conducted on a 2-stage axial turbine at the Institute of Steam- and Gas Turbines, RWTH Aachen University. The flow field for different blade loadings has been determined at the inlet and outlet as well as between the two stages. Consequently, the inhomogeneity at the outlet of each stage, depending on the blade loading, may be investigated. The homogeneity at the outlet has been evaluated by using the secondary kinetic energy coefficient and the formation of the passage vortex has therefore been emphasized. Furthermore, the loading impact on the leakage mass flow and the leakage main flow interaction has been estimated. On this account, the pressure loss in each cavity within the labyrinth seal of the first shrouded rotor blades is detected. The impact on the efficiency of different loadings has moreover been determined. The efficiency has been ascertained by using 5-hole probes and temperature probes after each stage. The investigations mentioned above have been conducted on a 2D-blade profile and serve as a baseline for future profiled end wall studies. The goal of the endwall contoured blades shall reduce the passage vortex and with it, the under- and overturning which ultimately leads to a more homogeneous outflow from the stage.

Impact of Blade Flexibility on Wind Turbine Loads and Pitch Settings

2018 ◽  
Author(s):  
Jinge Chen ◽  
Xin Shen ◽  
Xiaocheng Zhu ◽  
Zhaohui Du
Keyword(s):  
Wind Turbine ◽  
Aerodynamic Force ◽  
Turbine Blades ◽  
Beam Theory ◽  
Power Production ◽  
Aerodynamic Loads ◽  
Operational Conditions ◽  
Wind Speeds ◽  
Geometrically Exact Beam ◽  
The Impact

Along with the upscaling tendency, lighter and so more flexible wind turbine blades are introduced for reducing cost of manufacture and materials. The flexible blade deforms under aerodynamic loads and in turn affects the flow field, arising the aero-elastic problems. In this paper, the impact of blade flexibility on the wind turbine loads, power production, and pitch actions is discussed. An aeroelastic model is developed for the study. A free wake vortex lattice model is used to calculate the aerodynamic loads, and a geometrically exact beam theory is adopted to compute the structural dynamics of the blade. The flap, lead-lag bending and torsion DOFs are all included and nonlinear effects due to large deflections are considered. The NREL 5MW reference wind turbine is analyzed. Influences of pure-bending and bending-torsion deformations of the blade on aerodynamic loads are compared. The aerodynamic force distributions under various wind speeds for rigid and flexible blades are also compared. The steady state deformations across the operational conditions are calculated, along with the rotor power production. Significant reduction of power is seen especially under large wind speeds, due to the blade twist deformations under torsion moments. Lower pitch angle settings should be applied to maintain the constant power.

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