On the potential of the ideal diffuser augmented wind turbine: an investigation by means of a momentum theory approach and of a free-wake ring-vortex actuator disk model

A systematic analysis of a single-rotor horizontal axis wind turbine aerodynamics is performed to obtain a realistic potential maximum efficiency. It is noted that by including the effects of swirl, viscosity and finite number of blades, the maximum aerodynamic efficiency of a HAWT is within a few percentage points of the efficiency of commercially-available turbines. The need for investigating windfarm (as a unit) aerodynamics is thus highlighted. An actuator disk model is developed and implemented in the OpenFOAM software suite. The model is validated against 1-D momentum theory, blade element momentum theory, as well as against experimental data. The validated actuator disk model is then used to investigate an interesting microscale meteorological phenomenon called “flow convergence” caused by an array of wind turbines. This phenomenon is believed to be caused by the drop of pressure in wind farms. Wind farm numerical simulations are conducted with various approximations to investigate and explain the flow convergence phenomenon.

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Developing the Actuator Disk Model to Predict the Fluid–Structure Interaction in Numerical Simulation of Multimegawatt Wind Turbine Blades

Journal of Energy Resources Technology ◽

10.1115/1.4044576 ◽

2019 ◽

Vol 142 (3) ◽

Author(s):

Ali Behrouzifar ◽

Masoud Darbandi

Keyword(s):

Numerical Methods ◽

Wind Turbine ◽

Fluid Structure Interaction ◽

Cone Angle ◽

Disk Model ◽

Fluid Structure ◽

Aerodynamic Loads ◽

Structure Interaction ◽

Actuator Disk ◽

Analytical Approaches

Abstract The fluid–structure interaction (FSI) is generally addressed in multimegawatt wind turbine calculations. From the fluid flow perspective, the semi-analytical approaches, like actuator disk (AD) model, were commonly used in wind turbine rotor calculations. Indeed, the AD model can effectively reduce the computational cost of full-scale numerical methods. Additionally, it can substantially improve the results of pure analytical methods. Despite its great advantages, the AD model has not been developed to simulate the FSI problem in wind turbine simulations. This study first examines the effect of constant (rigid) cone angle on the performance of the chosen benchmark wind turbine. As a major contribution, this work subsequently extends the rigid AD model to nonrigid applications to suitably simulate the FSI. The new developed AD-FSI solver uses the finite-volume method to calculate the aerodynamic loads and the beam theory to predict the structural behaviors. A benchmark megawatt wind turbine is simulated to examine the accuracy of the newly developed AD-FSI solver. Next, the results of this solver are compared with the results of other researchers, who applied various analytical and numerical methods to obtain their results. The comparisons indicate that the new developed solver calculates the aerodynamic loads reliably and predicts the blade deflection very accurately.

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Verification of the Axial Momentum Theory for Propellers with a Uniform Load Distribution

International Journal of Turbomachinery Propulsion and Power ◽

10.3390/ijtpp4020008 ◽

2019 ◽

Vol 4 (2) ◽

pp. 8 ◽

Cited By ~ 2

Author(s):

Rodolfo Bontempo ◽

Marcello Manna

Keyword(s):

Axial Velocity ◽

Momentum Equation ◽

Uniform Load ◽

Nonlinear Method ◽

Thrust Coefficient ◽

Disk Model ◽

Local Flow ◽

Momentum Theory ◽

Velocity Magnitude ◽

Free Wake

The paper provides an evaluation of the errors embodied in the Axial Momentum Theory (AMT) as applied to a uniformly loaded actuator disk model without wake rotation. Although this model exhibits some unphysical features, such as the tip singularity and the violation of the angular momentum equation, it is still considered a touchstone in the theoretical aerodynamics of propellers. To simplify the model, a purely mathematical assumption is commonly used in the differential form of the axial momentum equation, i.e., the contribution of the pressure forces on the lateral surface of the infinitesimal streamtubes swallowed by the disk is neglected. In this paper, the errors introduced by this simplifying assumption are evaluated by comparing the results of the AMT with those of a nonlinear method modelling the free wake as the superposition of ring vortices distributed along the wake boundary. Firstly, the validity of this method is verified in terms of global performance coefficients. Then, using a CFD approach, it is also verified in terms of local flow quantities. The comparison between the ring-vortices method and the AMT shows that, for a highly loaded propeller, significant errors exist in the axial velocity at the disk, especially near the tip. Moreover, despite the uniform load, the axial velocity at the disk varies in the radial direction. Instead, the velocity magnitude remains almost uniform only for values of the thrust coefficient lower than 1.

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NUMERICAL SIMULATION AND WAKE MODELING OF WIND TURBINE ROTOR AS AN ACTUATOR DISK

International Journal of Modern Physics Conference Series ◽

10.1142/s2010194512008914 ◽

2012 ◽

Vol 19 ◽

pp. 320-330

Author(s):

XIANG SHEN ◽

TONGGUANG WANG ◽

WEI ZHONG

Keyword(s):

Wind Turbine ◽

Axial Velocity ◽

Turbine Rotor ◽

Wake Flow ◽

Pressure Jump ◽

Actuator Disk ◽

Momentum Theory ◽

Viscous Shear ◽

Wind Turbine Rotor ◽

Wake Modeling

Numerical simulations of flow fields around the wind turbine rotor simplified as an actuator disk (AD) with zero thickness have been made to investigate the flow structure and wake development in different operation states. A N-S solver has been used and the energy extracted by the rotor is represented by a discontinuous pressure jump through the actuator disk. Axial pressure and velocity development from far upstream to far downstream is fully described by the simulations, which could never be obtained by the momentum theory. It is showed that there are significant differences in wake development between inviscid and viscous conditions. In inviscid simulations, the axial velocity keeps decreasing along the oncoming flow direction, which is consistent with the momentum theory. In viscous simulations, however, the axial velocity first decreases but then gradually recovers approaching to the undisturbed velocity, due to momentum transport from outer flow to wake flow by viscous shear effect. Based on the numerical analysis, the work of this paper is also focused on wake modeling. A new two-dimensional models based on nonlinear wake development has been developed, which is capable to describe the far wake more accurately.

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Full HAWT rotor CFD simulations using different RANS turbulence models compared with actuator disk and experimental measurements

10.5194/wes-2017-6 ◽

2017 ◽

Author(s):

Nikolaos Stergiannis ◽

Jeroen van Beeck ◽

Mark C. Runacres

Keyword(s):

Experimental Data ◽

Wind Turbine ◽

Turbine Rotor ◽

Operating Conditions ◽

Experimental Measurements ◽

Horizontal Axis Wind Turbine ◽

Cfd Simulations ◽

Disk Model ◽

Actuator Disk ◽

Wind Turbine Rotor

Abstract. The development of large-scale wind energy projects has created the demand for increasingly accurate and efficient models that limit a project's uncertainties and risk. Wake effects are of great importance and are relevant for the optimization of wind farms. Despite a growing body of research, there are still many open questions and challenges to overcome. In computational modelling, there are always numerous input parameters such as material properties, geometry, boundary conditions, initial conditions, turbulence modelling etc. whose estimation is difficult and their values are often inaccurate or uncertain. Due to the lack of information of several sources, e.g., uncertainties present in operating conditions as well as in the mathematical modelling, the computational output is also uncertain. It is therefore very important to validate the mathematical models with experiments performed in controlled conditions. In the present paper, the single wake characteristics of a Horizontal-Axis Wind Turbine Rotor (HAWT) and their spatial evolution are investigated with different Computational Fluid Dynamics (CFD) modelling approaches and compared to experimental measurements. The steady state 3-D Reynolds-Averaged Navier Stokes (RANS) equations are solved in the open-source platform OpenFOAM, using different turbulence closure schemes. For the full-rotor CFD simulations, the Multiple Reference Frames (MRF) approach was used to model the rotation of the blades. For the simplified cases, an actuator disk model was used with the experimentally measured thrust (CT) and power (CP) coefficient values. The performance of each modelling approach is compared with experimental wind tunnel wake measurements from the 4th blind test organized by NOWITECH and NORCOWE in 2015. Numerical results are compared with experimental data along three horizontal lines downstream, covering all the wake regions. Wake predictions are shown to be very sensitive to the choice of the RANS turbulence model. For most cases, the ADM under-predicts the velocity deficit, except for the case of RNG k-ε which showed a superb performance in the mid and far wake. The full wind turbine rotor simulations showed good agreement to the experimental data, mainly in the near wake, amplifying the differences between the simplified models.

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Numerical simulation of the Mexico wind turbine using the actuator disk model along with the 3D correction of aerodynamic coefficients in OpenFOAM

Renewable Energy ◽

10.1016/j.renene.2020.10.120 ◽

2021 ◽

Vol 163 ◽

pp. 2029-2036

Author(s):

Shayesteh Amini ◽

Mahmood Reza Golzarian ◽

Esmail Mahmoodi ◽

Andres Jeromin ◽

Mohammad Hossein Abbaspour-Fard

Keyword(s):

Numerical Simulation ◽

Wind Turbine ◽

Aerodynamic Coefficients ◽

Disk Model ◽

Actuator Disk

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Investigating wind turbine impacts on near-wake flow using profiling lidar data and large-eddy simulations with an actuator disk model

Journal of Renewable and Sustainable Energy ◽

10.1063/1.4928873 ◽

2015 ◽

Vol 7 (4) ◽

pp. 043143 ◽

Cited By ~ 32

Author(s):

Jeffrey D. Mirocha ◽

Daniel A. Rajewski ◽

Nikola Marjanovic ◽

Julie K. Lundquist ◽

Branko Kosović ◽

...

Keyword(s):

Wind Turbine ◽

Large Eddy Simulations ◽

Wake Flow ◽

Lidar Data ◽

Near Wake ◽

Disk Model ◽

Actuator Disk ◽

Large Eddy

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Large-Eddy Simulation of Yawed Wind-Turbine Wakes: Comparisons with Wind Tunnel Measurements and Analytical Wake Models

Energies ◽

10.3390/en12234574 ◽

2019 ◽

Vol 12 (23) ◽

pp. 4574 ◽

Cited By ~ 8

Author(s):

Mou Lin ◽

Fernando Porté-Agel

Keyword(s):

Wind Tunnel ◽

Large Eddy Simulation ◽

Wind Turbine ◽

Wind Farms ◽

Disk Model ◽

Actuator Disk ◽

Eddy Simulation ◽

Large Eddy ◽

Wind Tunnel Measurements ◽

Tangential Forces

In this study, we validated a wind-turbine parameterisation for large-eddy simulation (LES) of yawed wind-turbine wakes. The presented parameterisation is modified from the rotational actuator disk model (ADMR), which takes account of both thrust and tangential forces induced by a wind turbine based on the blade-element theory. LES results using the yawed ADMR were validated with wind-tunnel measurements of the wakes behind a stand-alone miniature wind turbine model with different yaw angles. Comparisons were also made with the predictions of analytical wake models. In general, LES results using the yawed ADMR are in good agreement with both wind-tunnel measurements and analytical wake models regarding wake deflections and spanwise profiles of the mean velocity deficit and the turbulence intensity. Moreover, the power output of the yawed wind turbine is directly computed from the tangential forces resolved by the yawed ADMR, in contrast with the indirect power estimation used in the standard actuator disk model. We found significant improvement in the power prediction from LES using the yawed ADMR over the simulations using the standard actuator disk without rotation, suggesting a good potential of the yawed ADMR to be applied in LES studies of active yaw control in wind farms.

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A BEM-Based Actuator Disk Model for Wind Turbine Wakes Considering Atmospheric Stability

10.20944/preprints201907.0029.v1 ◽

2019 ◽

Author(s):

Xing Xing Han ◽

De You Liu ◽

Chang Xu ◽

Wen Zhong Shen ◽

Lin Min Li ◽

...

Keyword(s):

Wind Turbine ◽

Wind Farm ◽

Atmospheric Stability ◽

Stability Conditions ◽

High Fidelity ◽

Thrust Coefficient ◽

Disk Model ◽

Similarity Functions ◽

Actuator Disk ◽

Blade Element

Atmospheric stability affects wind turbine wakes significantly. High-fidelity approaches such as large eddy simulations (LES) with the actuator line (AL) model which predicts detailed wake structures, fail to be applied in wind farm engineering applications due to its expensive cost. In order to make wind farm simulations computationally affordable, this paper proposes a new actuator disk model (AD) based on the blade element method (BEM) and combined with Reynolds-averaged Navier–Stokes equations (RANS) to model turbine wakes under different atmospheric stability conditions. In the proposed model, the upstream reference velocity is firstly estimated from the disk averaged velocity based on the one-dimensional momentum theory, and then is used to evaluate the rotor speed to calculate blade element forces. Flow similarity functions based on field measurement are applied to limit wind shear under strongly stable conditions, and turbulence source terms are added to take the buoyant-driven effects into consideration. Results from the new AD model are compared with field measurements and results from the AD model based on the thrust coefficient, the BEM-AD model with classical similarity functions and a high-fidelity LES approach. The results show that the proposed method is better in simulating wakes under various atmospheric stability conditions than the other AD models and has a similar performance to the high-fidelity LES approach however in much lower computational cost.

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Understanding the Influence of Turbine Geometry and Atmospheric Turbulence on Wind Turbine Wakes

Volume 6B: Energy ◽

10.1115/imece2016-67421 ◽

2016 ◽

Author(s):

Ping Gu ◽

Jim Y. J. Kuo ◽

David A. Romero ◽

Cristina H. Amon

Keyword(s):

Wind Turbine ◽

Atmospheric Turbulence ◽

Aerodynamic Force ◽

Atmospheric Condition ◽

Atmospheric Effects ◽

Wake Region ◽

Near Wake ◽

Disk Model ◽

Actuator Disk ◽

Far Wake

A wind turbine wake is divided into two regions, near wake and far wake. In the near wake region, the flow is highly turbulent and is strongly influenced by the rotor geometry. In the far wake region, the influence of rotor geometry becomes less important as atmospheric effects become dominant. However, how turbine geometry and atmospheric condition affect the two wake regions is not well studied. In this work, the influence of atmospheric turbulence and the blade aerodynamic forces on wake development is studied using computational fluid dynamics (CFD) models. The CFD simulation results are based on an actuator disk model and an k–ε turbulence model. The effects of blade geometry are captured by prescribing aerodynamics forces exerted by a LM8.2 blade on an actuator disk, and are compared with that of an equivalent uniform normalized force, under two atmospheric turbulence conditions. The finding shows that the length of the near wake region is strongly affected by atmospheric turbulence, with the wake becoming fully developed as far as 2.5 rotor diameters downstream of the rotor under low turbulence conditions. Furthermore, the velocity profile in the far wake region is independent of the blade profile. In other words, in the cases studied, an actuator disk with an equivalent uniform force will produce nearly identical velocity profiles in the far wake region as one with nonuniform aerodynamic force profiles. These findings have implications on existing wake models where the far wake is the region of interest. Specifically, the beginning of the far wake region should be properly defined for each scenario, and that it is not necessary to provide detailed rotor geometry for far wake simulations.

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