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Pierre-elouan Réthoré – One of the best experts on this subject based on the ideXlab platform.

Curran Crawford – One of the best experts on this subject based on the ideXlab platform.

  • Tuned Actuator Disk approach for predicting tidal turbine performance with wake interaction
    International Journal of Marine Energy, 2017
    Co-Authors: Michael Shives, Curran Crawford
    Abstract:

    Abstract This article presents a practical method for predicting the power output of tidal farms with device wake interactions. The method uses Reynolds-averaged Navier-Stokes (RANS) simulations to predict turbine wakes and bathymetry effects. The power of each turbine depends on the local velocity, which is influenced by other turbine wakes. Therefore, the accuracy of power predictions depends heavily on proper wake modeling. This is a critical issue for the tidal power industry because best practice for predicting tidal farm energy yield has yet to be established, and wake interaction effects may drastically alter energy yield in a dense turbine farm. This article introduces a methodology which accurately predicts power output while minimizing computational expense, named the tuned Actuator Disk approach (TADA). Rotors are resolved using 9–15 elements across their diameter, allowing for very fast simulations of multiple turbines. The model is tuned to match known thrust and power operational profiles for a set of calibration cases based either on experiments or a limited set of high-resolution simulations. In this study, TADA was used to model a tandem configuration of two scaled rotors in a flume tank, and gave accurate predictions of the rotor thrust, power and wake velocities. Predictions of thrust and power became independent of grid density with more than 15 elements spanning the rotor diameter, however errors associated with using 9 elements were limited to 3% for thrust and 6% for power. Once calibrated for a specific turbine and computational mesh, TADA can be used in full farm-scale simulations at reasonable computational expense, which is an important capability for predicting tidal farm energy yield.

  • adapted two equation turbulence closures for Actuator Disk rans simulations of wind tidal turbine wakes
    Renewable Energy, 2016
    Co-Authors: Michael Shives, Curran Crawford
    Abstract:

    Abstract Reliable methods for modelling wake recovery within a farm of wind or tidal turbines are critical for obtaining accurate estimates of annual enerenergy production, and for detailed farm layout optimization. These are important objectives for maximizing energy yield while minimizing costs. Computational fluifluid dynamics (CFD) simulation is rapidly being adopted as a tool for flow modelling in wind and tidal farms, gaining favour over more traditional and simpler empirically-determined wake models. The most practical methodology for CFD simulations of turbine farms uses an Actuator Disk (AD) representation for each rotor, which imposes the rotor forces by adding source terms to the governing equations rather than explicitly resolving the flow over the turbine blades. It is well understood that when using the AD approach, standard turbulence models tend to predict faster wake recovery than is observed in real flows. Thus, the standard CFD turbulence models must be adapted for use with the AD methodology. Additionally, because of the manner in which the AD approach distributes the rotor forces, it cannot resolve the system of discrete vortices trailed from the blade tips. This article presents two contributions to improving AD simulations of wind/tidal turbine wakes. The first is identifying that the well-established k – ω SST turbulence model is appropriate for AD simulations because it mitigates the problem of over-predicting the initial wake recovery rate. The second contribution is a method to include the typically un-modelled production of turbulent kinetic energy due to the breakdown of trailed vortices. This method was tuned to minimize the wake error for three experimental test cases with different rotors and different ambient turbulence intensities {3,10,15}%. The new model was validated and compared to existing turbulence methods for the wake of a second rotor in a tandem array configuration with different separation distances and ambient turbulence intensities. The different models were assessed using an error metric designed to estimate the error in predicting the power production of a turbine array. The reduction of this error by the new model varied from case to case, but was on the order of 3.5–10%, compared to the standard k – e model.

  • Adapted two-equation turbulence closures for Actuator Disk RANS simulations of wind & tidal turbine wakes
    Renewable Energy, 2016
    Co-Authors: Michael Shives, Curran Crawford
    Abstract:

    Abstract Reliable methods for modelling wake recovery within a farm of wind or tidal turbines are critical for obtaining accurate estimates of annual enerenergy production, and for detailed farm layout optimization. These are important objectives for maximizing energy yield while minimizing costs. Computational fluifluid dynamics (CFD) simulation is rapidly being adopted as a tool for flow modelling in wind and tidal farms, gaining favour over more traditional and simpler empirically-determined wake models. The most practical methodology for CFD simulations of turbine farms uses an Actuator Disk (AD) representation for each rotor, which imposes the rotor forces by adding source terms to the governing equations rather than explicitly resolving the flow over the turbine blades. It is well understood that when using the AD approach, standard turbulence models tend to predict faster wake recovery than is observed in real flows. Thus, the standard CFD turbulence models must be adapted for use with the AD methodology. Additionally, because of the manner in which the AD approach distributes the rotor forces, it cannot resolve the system of discrete vortices trailed from the blade tips. This article presents two contributions to improving AD simulations of wind/tidal turbine wakes. The first is identifying that the well-established k – ω SST turbulence model is appropriate for AD simulations because it mitigates the problem of over-predicting the initial wake recovery rate. The second contribution is a method to include the typically un-modelled production of turbulent kinetic energy due to the breakdown of trailed vortices. This method was tuned to minimize the wake error for three experimental test cases with different rotors and different ambient turbulence intensities {3,10,15}%. The new model was validated and compared to existing turbulence methods for the wake of a second rotor in a tandem array configuration with different separation distances and ambient turbulence intensities. The different models were assessed using an error metric designed to estimate the error in predicting the power production of a turbine array. The reduction of this error by the new model varied from case to case, but was on the order of 3.5–10%, compared to the standard k – e model.

Xiaolei Yang – One of the best experts on this subject based on the ideXlab platform.

  • Evaluation of Actuator Disk Model Relative to Actuator Surface Model for Predicting Utility-Scale Wind Turbine Wakes
    Energies, 2020
    Co-Authors: Xiaolei Yang
    Abstract:

    The Actuator Disk (AD) model is widely used in Large-Eddy Simulations (LES) to simulate wind turbturbine wakes because of its computing efficiency. The capability of the AD model in predicting time-average quantities of wind tunnel-scale turbines has been assessed extensively in the literature. However, its capability in predicting wakes of utility-scale wind turbturbines especially for the coherent flow structures is not clear yet. In this work, we take the time-averaged statistics and Dynamic Mode Decomposition (DMD) modes computed from a well-validated Actuator Surface (AS) model as references to evaluate the capability of the AD model in predicting the wake of a 2.5 MW utility-scale wind turbturbine for uniform inflow and fully developed turbulent inflow conditions. For the uniform inflow cases, the predictions from the AD model are significantly different from those from the AS model for the time-averaged velocity, and the turbulence kinetic energy until nine rotor diameters (D) downstream of the turbine. For the turbulent inflow cases, on the other hand, the differences in the time-averaged quantities predicted by the AS and AD models are not significant especially at far wake locations. As for DMD modes, significant differences are observed in terms of dominant frequencies and DMD patterns for both inflows. Moreover, the effects of incoming large eddies, bluff body shear layer instability, and hub vortexes on the coherent flow structures are discussed in this paper.

  • On the predictive capabilities of LES-Actuator Disk model in simulating turbulence past wind turbines and farms
    2013 American Control Conference, 2013
    Co-Authors: Xiaolei Yang, Fotis Sotiropoulos
    Abstract:

    In this paper, we validate an LES (large-eddy simulation)-Actuator Disk model by comparing the computed results with wind tunnel measurements for both stand-alone wind turbturbine case and wind farm case. In the Actuator Disk model, the forces are uniformly distributed. The effects of rotation and the effects of nacelle and tower are not taken into account. Dynamic subgrid scale model is employed in the LES. For the stand-alone wind turbturbine case, grid refinement studies with three different resolutions are performed. Discrepancies with the wind tunnel measurements are observed in the near wake locations (2D and 3D downstream). However, very good agreements with the wind tunnel measurements are obtained for further downstream locations. For the wind farm case, overall good agreements with the wind tunnel measurements are obtained for the streamwise variations of the streamwise mean velocity and the streamwise turbulence intensity at the bottom and top heights of wind turbturbines. Some discrepancies with the wind tunnel measurements are observed at the hub height of wind turbturbines.

  • ACC – On the predictive capabilities of LES-Actuator Disk model in simulating turbulence past wind turbines and farms
    2013 American Control Conference, 2013
    Co-Authors: Xiaolei Yang, Fotis Sotiropoulos
    Abstract:

    In this paper, we validate an LES (large-eddy simulation)-Actuator Disk model by comparing the computed results with wind tunnel measurements for both stand-alone wind turbturbine case and wind farm case. In the Actuator Disk model, the forces are uniformly distributed. The effects of rotation and the effects of nacelle and tower are not taken into account. Dynamic subgrid scale model is employed in the LES. For the stand-alone wind turbturbine case, grid refinement studies with three different resolutions are performed. Discrepancies with the wind tunnel measurements are observed in the near wake locations (2D and 3D downstream). However, very good agreements with the wind tunnel measurements are obtained for further downstream locations. For the wind farm case, overall good agreements with the wind tunnel measurements are obtained for the streamwise variations of the streamwise mean velocity and the streamwise turbulence intensity at the bottom and top heights of wind turbturbines. Some discrepancies with the wind tunnel measurements are observed at the hub height of wind turbturbines.

Charles Meneveau – One of the best experts on this subject based on the ideXlab platform.

  • Comparison of wind farm large eddy simulations using Actuator Disk and Actuator line models with wind tunnel experiments
    Renewable Energy, 2018
    Co-Authors: Richard J. A. M. Stevens, Luis A. Martínez-tossas, Charles Meneveau
    Abstract:

    We compare wind farm large eddy simulations with the EPFL wind tunnel measurement by Chamorro and Porte-Agel (Bound-Lay. Meteorol. 136, 515 (2010) and Energies 4, 1916 (2011)). We find that the near turbine wake, up to 3 turbine diameters downstream, of a single turbine is captured better with the Actuator line method than using the Actuator Disk method. Further downstream the results obtained with both models agrees very well with the experimental data, confirming findings from previous studies. For large aligned wind farms we find that the Actuator Disk model predicts the wake profiles behind turbines on the second and subsequent rows more accurately than the wake profile behind the first turbine row. The reason is that the wake layer profile that is created at hub height in very large wind farms is closer to the assumptions made in the Actuator Disk model than the logarithmic profile found in the inflow conditions. In addition, we show that, even in relatively coarse resolution simulations, adding the effect of the turbine nacelle and tower leads to a significant improvement in the prediction of the near wake features at 1 and 2 diameters downstream.

  • wake structure in Actuator Disk models of wind turbines in yaw under uniform inflow conditions
    Journal of Renewable and Sustainable Energy, 2016
    Co-Authors: Michael F Howland, Juliaan Bossuyt, Luis A Martineztossas, Johan Meyers, Charles Meneveau
    Abstract:

    Reducing wake losses in wind farms by deflecting the wakes through turbine yawing has been shown to be a feasible wind farm controls approach. Nonetheless, the effectiveness of yawing depends not only on the degree of wake deflection but also on the resulting shape of the wake. In this work, the deflection and morphology of wakes behind a porous Disk model of a wind turbturbine operating in yawed conditions are studied using wind tunnel experiments and uniform inflow. First, by measuring velocity distributions at various downstream positions and comparing with prior studies, we confirm that the non-rotating porous Disk wind turbturbine model in yaw generates realistic wake deflections. Second, we characterize the wake shape and make observations of what is termed as curled wake, displaying significant spanwise asymmetry. The wake curling observed in the experiments is also reproduced qualitatively in Large Eddy Simulations using both Actuator Disk and Actuator line models. Results suggest that when a wind turbturbine is yawed for the benefit of downstream turbines, the curled shape of the wake and its asymmetry must be taken into account since it affects how much of it intersects the downstream turbines.

Michael Shives – One of the best experts on this subject based on the ideXlab platform.

  • Tuned Actuator Disk approach for predicting tidal turbine performance with wake interaction
    International Journal of Marine Energy, 2017
    Co-Authors: Michael Shives, Curran Crawford
    Abstract:

    Abstract This article presents a practical method for predicting the power output of tidal farms with device wake interactions. The method uses Reynolds-averaged Navier-Stokes (RANS) simulations to predict turbine wakes and bathymetry effects. The power of each turbine depends on the local velocity, which is influenced by other turbine wakes. Therefore, the accuracy of power predictions depends heavily on proper wake modeling. This is a critical issue for the tidal power industry because best practice for predicting tidal farm energy yield has yet to be established, and wake interaction effects may drastically alter energy yield in a dense turbine farm. This article introduces a methodology which accurately predicts power output while minimizing computational expense, named the tuned Actuator Disk approach (TADA). Rotors are resolved using 9–15 elements across their diameter, allowing for very fast simulations of multiple turbines. The model is tuned to match known thrust and power operational profiles for a set of calibration cases based either on experiments or a limited set of high-resolution simulations. In this study, TADA was used to model a tandem configuration of two scaled rotors in a flume tank, and gave accurate predictions of the rotor thrust, power and wake velocities. Predictions of thrust and power became independent of grid density with more than 15 elements spanning the rotor diameter, however errors associated with using 9 elements were limited to 3% for thrust and 6% for power. Once calibrated for a specific turbine and computational mesh, TADA can be used in full farm-scale simulations at reasonable computational expense, which is an important capability for predicting tidal farm energy yield.

  • adapted two equation turbulence closures for Actuator Disk rans simulations of wind tidal turbine wakes
    Renewable Energy, 2016
    Co-Authors: Michael Shives, Curran Crawford
    Abstract:

    Abstract Reliable methods for modelling wake recovery within a farm of wind or tidal turbines are critical for obtaining accurate estimates of annual energy production, and for detailed farm layout optimization. These are important objectives for maximizing energy yield while minimizing costs. Computational fluid dynamics (CFD) simulation is rapidly being adopted as a tool for flow modelling in wind and tidal farms, gaining favour over more traditional and simpler empirically-determined wake models. The most practical methodology for CFD simulations of turbine farms uses an Actuator Disk (AD) representation for each rotor, which imposes the rotor forces by adding source terms to the governing equations rather than explicitly resolving the flow over the turbine blades. It is well understood that when using the AD approach, standard turbulence models tend to predict faster wake recovery than is observed in real flows. Thus, the standard CFD turbulence models must be adapted for use with the AD methodology. Additionally, because of the manner in which the AD approach distributes the rotor forces, it cannot resolve the system of discrete vortices trailed from the blade tips. This article presents two contributions to improving AD simulations of wind/tidal turbine wakes. The first is identifying that the well-established k – ω SST turbulence model is appropriate for AD simulations because it mitigates the problem of over-predicting the initial wake recovery rate. The second contribution is a method to include the typically un-modelled production of turbulent kinetic energy due to the breakdown of trailed vortices. This method was tuned to minimize the wake error for three experimental test cases with different rotors and different ambient turbulence intensities {3,10,15}%. The new model was validated and compared to existing turbulence methods for the wake of a second rotor in a tandem array configuration with different separation distances and ambient turbulence intensities. The different models were assessed using an error metric designed to estimate the error in predicting the power production of a turbine array. The reduction of this error by the new model varied from case to case, but was on the order of 3.5–10%, compared to the standard k – e model.

  • Adapted two-equation turbulence closures for Actuator Disk RANS simulations of wind & tidal turbine wakes
    Renewable Energy, 2016
    Co-Authors: Michael Shives, Curran Crawford
    Abstract:

    Abstract Reliable methods for modelling wake recovery within a farm of wind or tidal turbines are critical for obtaining accurate estimates of annual energy production, and for detailed farm layout optimization. These are important objectives for maximizing energy yield while minimizing costs. Computational fluid dynamics (CFD) simulation is rapidly being adopted as a tool for flow modelling in wind and tidal farms, gaining favour over more traditional and simpler empirically-determined wake models. The most practical methodology for CFD simulations of turbine farms uses an Actuator Disk (AD) representation for each rotor, which imposes the rotor forces by adding source terms to the governing equations rather than explicitly resolving the flow over the turbine blades. It is well understood that when using the AD approach, standard turbulence models tend to predict faster wake recovery than is observed in real flows. Thus, the standard CFD turbulence models must be adapted for use with the AD methodology. Additionally, because of the manner in which the AD approach distributes the rotor forces, it cannot resolve the system of discrete vortices trailed from the blade tips. This article presents two contributions to improving AD simulations of wind/tidal turbine wakes. The first is identifying that the well-established k – ω SST turbulence model is appropriate for AD simulations because it mitigates the problem of over-predicting the initial wake recovery rate. The second contribution is a method to include the typically un-modelled production of turbulent kinetic energy due to the breakdown of trailed vortices. This method was tuned to minimize the wake error for three experimental test cases with different rotors and different ambient turbulence intensities {3,10,15}%. The new model was validated and compared to existing turbulence methods for the wake of a second rotor in a tandem array configuration with different separation distances and ambient turbulence intensities. The different models were assessed using an error metric designed to estimate the error in predicting the power production of a turbine array. The reduction of this error by the new model varied from case to case, but was on the order of 3.5–10%, compared to the standard k – e model.