Comparison of CFD Prediction and Actual Condition for Wake Effect on an Onshore Wind Farm (original) (raw)
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Wind Energy, 2012
Computational fluid dynamic (CFD) methods are used in this paper to predict the power production from entire wind farms in complex terrain and to shed some light into the wake flow patterns. Two full 3D Navier-Stokes solvers for incompressible fluid flow, employing k-ε and k-ω turbulence closures, are used. The wind turbines are modelled as momentum absorbers by means of their thrust coefficient through the actuator disk approach. Alternative methods for estimating the reference wind speed in the calculation of the thrust are tested. The work presented in this paper is part of the work being undertaken within the UpWind Integrated Project that aims to develop the design tools for next generation of large wind turbines. In this part of UpWind, the performance of wind farm and wake models is being examined in complex terrain environment where there are few pre-existing relevant measurements. The focus of the work carried out is to evaluate the performance of CFD models in large wind farm applications in complex terrain and to examine the development of the wakes in a complex terrain environment.
CFD wind turbines wake assessment in complex topography
Energy Conversion and Management, 2017
The purpose of this work is to numerically study the wind turbine wake evolution in farm over both complex and flat terrain. The nonlinear, aerodynamic interaction between the rotor wake and the wind farm terrain is modeled using the Hybrid method combining CFD (Computational Fluid dynamics) with the actuator disk model. The rotor defined as a function of the wind speed and the thrust coefficient is applied through a source term added in Navier-Stokes equations within (RANS) decomposition. The framework is structured and resolved via an Open Source Computational fluid dynamics program based on the finite volume method. The interactions between atmospheric upwind boundary layer, downwind wake and ground effects are evaluated considering different wind farm configurations: First, simulations are conducted for flat terrain by varying the wind turbine hub height. The soil effects on the wake evolution are estimated by means of the size length of the eddy areas of low speed recorded behind the rotor. In the second configuration concerning the complex terrain, the proposed hybrid method is adapted to the local wind field significantly disturbed by the topography singularities. The flow field obtained at the hub level is then analyzed and used to define the corresponding actuator disk model. This approach is applied to a small region located in north of Algeria. However, the accuracy and performance of the proposed model to predict the near wake and the far wake are demonstrated by a comparison with wake measurement over flat terrain and are in good agreement with experimental data. Results obtained in all cases gives interesting information involved in wind farm layout.
CFD Investigations of Wake Flow Interactions in a Wind Farm with 14 Wind Turbines
International Journal of Offshore and Polar Engineering, 2020
Because the wake flow interaction phenomenon among wind turbines has a great influence on aerodynamic power output, wind speed deficit turbulence stress, and wake vortex structure, the wake interaction for the optimal arrangement of wind farm has recently attracted increasing attention. This paper presents a validation of aerodynamics for the two offset model wind turbines on the actuator line model and computational fluid dynamics (CFD) technique. The numerical results of the present simulations are compared with those produced by testing on Blind Test 3 and other simulation models. On the basis of the simulations results, the present study shows good agreement with the experimental results. Besides, considering the uniform inflow condition, a numerical method is harnessed to simulate the complex phenomenon of wake interaction in a wind farm containing 14 wind turbines. Large eddy simulations combined with an actuator line model are conducted in the in-house CFD code FOWT-UALM-SJTU solver, which is an extension based on OpenFOAM. The motivation for this work is to create a sound methodology for performing the simulation of large wind farms. To better understand the wake interaction phenomenon, the aerodynamic power coefficients and basic features of both the near and far wake, including the distribution characteristics of the mean wake velocity and vortex structures, are studied in detail.
Energy Procedia, 2013
In this work a practical approach to Computational Fluid Dynamics (CFD) simulations in wind resource evaluation is proposed in a test case of the IEA project (task 31) "Wakebench" focused on the benchmarking of wind wakes models. The proposed method uses an easy wake model, the Actuator Disc (AD), in a CFD approach, in order to understand the wind behavior in a complex wind farm of 18 turbines sited in the northern part of Netherlands, with a sustainable computational load. In order to optimize the simulation results a useful tool that automates the parameters evolution was developed; such tool is able to improve the control of the engineering parameters and is useful to prepare advanced post processing. The study was mainly focused on the analysis of the single wake; also simulations on the double wake case and other tests on larger wind farm were performed with success using the same automatic approach. Results are in quite good agreement with experimental data and the differences between the predicted and experimental results are to be addressed to: global effect of stability, turbine inferences in the actual wind farm and to some lacks in physical wake model.
Survey of modelling methods for wind turbine wakes and wind farms
Wind Energy, 1999
This article provides an overview and analysis of different wake-modelling methods which may be used as prediction and design tools for both wind turbines and wind farms. We also survey the available data concerning the measurement of wind magnitudes in both single wakes and wind farms, and of loading effects on wind turbines under single-and multiple-wake conditions. The relative merits of existing wake and wind farm models and their ability to reproduce experimental results are discussed. Conclusions are provided concerning the usefulness of the different modelling approaches examined, and dif®cult issues which have not yet been satisfactorily treated and which require further research are discussed.
Journal of Wind Engineering and Industrial Aerodynamics, 2013
Experimental results on the wake properties of a non-rotating simplified wind turbine model, based on the actuator disc concept, and a rotating model, a three-blade wind turbine, are presented. Tests were performed in two different facilities, one providing a nominally Decaying Isotropic Turbulent inflow (turbulence intensity of 4% at rotor disc location) and one providing a neutral atmospheric boundary layer above a moderately rough terrain at a geometric scale of 1 : 300 (determined from the combination of several indicators), with 13% of turbulence intensity at hub height). The objective is to determine the limits of the simplified wind turbine model to reproduce a realistic wind turbine wake. Pressure and high-order velocity statistics are therefore compared in the wake of both rotor discs for two different inflow conditions in order to quantify the influence of the ambient turbulence. It has been shown that wakes of rotating model and porous disc developing in the modelled atmospheric boundary layer are indistinguishable after 3 diameters downstream of the rotor discs, whereas few discrepancies are still visible at the same distance with the Decaying Isotropic Turbulent inflow.
Numerical Computations of Wind Turbine Wakes
Wind Energy, 2007
Numerical simulations of the Navier-Stokes equations are performed to achieve a better understanding of the behaviour of wakes generated by wind turbines. The simulations are performed by combining the in-house developed computer code EllipSys3D with the actuator line and disc methodologies. In the actuator line and disc methods the blades are represented by a line or a disc on which body forces representing the loading are introduced. The body forces are determined by computing local angles of attack and using tabulated aerofoil coefficients. The advantage of using the actuator disc technique is that it is not necessary to resolve blade boundary layers. Instead the computational resources are devoted to simulating the dynamics of the flow structures.
Wakes Calculation in a Offshore Wind Farm
Wind Engineering, 2013
This paper is focusing on the wake modeling in large offshore wind farms. Over the sea the ambient turbulence is much lower than onshore, wakes persist for long distances, mixing in a complex pattern. Hence an accurate evaluation of the wakes become crucial in the estimation both of the production and loads. Regarding loads the main effect of the turbines wakes is an increase of turbulence compared to the ambient one. A careful assessment of the wakes is therefore required when analyzing offshore wind farms. The approaches in estimating the wake losses go from simple theoretical or empirical laws to full rotor aerodynamic calculations; in between there is a range of intermediate calculations. Two approaches will be presented: the use of relative simple equations (also called analytical models) which are the standards in the wind resource assessment and a more accurate, but computationally more demanding, the actuator disc technique.