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Blade Element Momentum

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Ernesto Benini – One of the best experts on this subject based on the ideXlab platform.

Gabriele Bedon – One of the best experts on this subject based on the ideXlab platform.

Ian Masters – One of the best experts on this subject based on the ideXlab platform.

  • comparison of synthetic turbulence approaches for Blade Element Momentum theory prediction of tidal turbine performance and loads
    Renewable Energy, 2020
    Co-Authors: Michael Togneri, Gregory Pinon, Clement Carlier, Ian Masters
    Abstract:

    Abstract Turbulence is a crucial flow phenomenon for tidal energy converters (TECs), as it influences both the peak loads they experience and their fatigue life. To best mitigate its effects we must understand both turbulence itself and how it induces loads on TECs. To that end, this paper presents the results of Blade Element Momentum theory (BEMT) simulations of flume-scale TEC models subjected to synthetic turbulent flows. Synthetic turbulence methods produce three-dimensional flowfields from limited data, without solving the equations governing fluid motion. These flowfields are non-physical, but match key statistical properties of real turbulence and are much quicker and computationally cheaper to produce. This study employs two synthetic turbulence generation methods: the synthetic eddy method and the spectral Sandia method. The response of the TECs to the synthetic turbulence is predicted using a robust BEMT model, modified from the classical formulation of BEMT. We show that, for the cases investigated, TEC load variability is lower in stall operation than at higher tip speed ratios. The variability of turbine loads has a straightforward relationship to the turbulence intensity of the inflow. Spectral properties of the velocity field are not fully reflected in the spectra of TEC loads.

  • Planning tidal stream turbine array layouts using a coupled Blade Element Momentum – computational fluid dynamics model
    Renewable Energy, 2014
    Co-Authors: Rami Malki, Ian Masters, Alison Williams, T.n. Croft
    Abstract:

    A coupled Blade Element Momentumcomputational fluifluid dynamics (BEM–CFD) model is used to conduct simulations of groups of tidal stream turbines. Simulations of single, double and triple turbine arrangements are conducted first to evaluate the effects of turbine spacing and arrangement on flow dynamics and rotor performance. Wake recovery to free-stream conditions was independent of flow velocity. Trends identified include significant improvement of performance for the downstream rotor where longitudinal spacing between a longitudinally aligned pair is maximised, whereas maintaining a lateral spacing between two devices of two diameters or greater increases the potential of benefitting from flow acceleration between them. This could significantly improve the performance of a downstream device, particularly where the longitudinal spacing between the two rows is two diameters or less. Due to the computational efficiency of this modelling approach, particularly when compared to transient computational fluifluid dynamics simulations of rotating Blades, the BEM–CFD model can simulate larger numbers of devices. An example of how an understanding of the hydrodynamics around devices is affected by rotor spacing can be used to optimise the performance of a 14 turbine array is presented. Compared to a regular staggered configuration, the total power output of the array was increased by over 10%.

  • cavitation inception and simulation in Blade Element Momentum theory for modelling tidal stream turbines
    Proceedings of the Institution of Mechanical Engineers Part A: Journal of Power and Energy, 2013
    Co-Authors: Hannah Buckland, Ian Masters, J A C Orme, Tim Baker
    Abstract:

    Blade Element Momentum theory (BEMT) is an analytical modelling tool that describes the performance of turbines by cross-referencing one-dimensional Momentum theory with Blade Element theory. Each Blade is discretised along its length and the dynamic properties of torque and axial force are determined. A compatible cavitation detection model is introduced to indicate any cavitating Blade Elements. Cavitation occurrence is dependent on proximity to the free surface, the incident flow velocity and inflow angle and the Blade cross-section aerofoil shape. The shock waves associated with cavitation can significantly damage the Blade surface and reduce performance; therefore, this model is a useful addition to BEMT and can be used in turbine design to minimise cavitation occurrence. The results are validated using the cavitation experiment observations.

Rami Malki – One of the best experts on this subject based on the ideXlab platform.

  • planning tidal stream turbine array layouts using a coupled Blade Element Momentum computational fluid dynamics model
    Renewable Energy, 2014
    Co-Authors: Rami Malki, I. Masters, A J Williams, Nick T Croft
    Abstract:

    A coupled Blade Element Momentumcomputational fluifluid dynamics (BEM–CFD) model is used to conduct simulations of groups of tidal stream turbines. Simulations of single, double and triple turbine arrangements are conducted first to evaluate the effects of turbine spacing and arrangement on flow dynamics and rotor performance. Wake recovery to free-stream conditions was independent of flow velocity. Trends identified include significant improvement of performance for the downstream rotor where longitudinal spacing between a longitudinally aligned pair is maximised, whereas maintaining a lateral spacing between two devices of two diameters or greater increases the potential of benefitting from flow acceleration between them. This could significantly improve the performance of a downstream device, particularly where the longitudinal spacing between the two rows is two diameters or less. Due to the computational efficiency of this modelling approach, particularly when compared to transient computational fluifluid dynamics simulations of rotating Blades, the BEM–CFD model can simulate larger numbers of devices. An example of how an understanding of the hydrodynamics around devices is affected by rotor spacing can be used to optimise the performance of a 14 turbine array is presented. Compared to a regular staggered configuration, the total power output of the array was increased by over 10%.

  • Planning tidal stream turbine array layouts using a coupled Blade Element Momentum – computational fluid dynamics model
    Renewable Energy, 2014
    Co-Authors: Rami Malki, Ian Masters, Alison Williams, T.n. Croft
    Abstract:

    A coupled Blade Element Momentum – computational fluid dynamics (BEM–CFD) model is used to conduct simulations of groups of tidal stream turbines. Simulations of single, double and triple turbine arrangements are conducted first to evaluate the effects of turbine spacing and arrangement on flow dynamics and rotor performance. Wake recovery to free-stream conditions was independent of flow velocity. Trends identified include significant improvement of performance for the downstream rotor where longitudinal spacing between a longitudinally aligned pair is maximised, whereas maintaining a lateral spacing between two devices of two diameters or greater increases the potential of benefitting from flow acceleration between them. This could significantly improve the performance of a downstream device, particularly where the longitudinal spacing between the two rows is two diameters or less. Due to the computational efficiency of this modelling approach, particularly when compared to transient computational fluid dynamics simulations of rotating Blades, the BEM–CFD model can simulate larger numbers of devices. An example of how an understanding of the hydrodynamics around devices is affected by rotor spacing can be used to optimise the performance of a 14 turbine array is presented. Compared to a regular staggered configuration, the total power output of the array was increased by over 10%.

  • a coupled Blade Element Momentum computational fluid dynamics model for evaluating tidal stream turbine performance
    Applied Mathematical Modelling, 2013
    Co-Authors: Rami Malki, A J Williams, T.n. Croft, Michael Togneri, I. Masters
    Abstract:

    Abstract A modelling approach based on Blade Element Momentum theory is developed for the prediction of tidal stream turbine performance in the ocean environment. Through the coupling of the Blade Element Momentum method with computational fluifluid dynamics, the influence of upstream hydrodynamics on rotor performance is accounted for. Incoming flow onto the rotor can vary in speed and direction compared to free-stream conditions due to the presence of obstructions to the flow in the upstream, due to other devices for example, or due to the complexity of natural bathymetries. The relative simplicity of the model leads to short run times and a lower demand on computational resources making it a useful tool for considering more complex engineering problems consisting of multiple tidal stream turbines. Results from the model compare well against both measured data from flume experiments and results obtained using the classical Blade Element Momentum model. A discussion considering the advantages and disadvantages of these different approaches is included.

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

  • a fast stochastic solution method for the Blade Element Momentum equations for long term load assessment
    Wind Energy, 2018
    Co-Authors: Manuel Fluck, Curran Crawford
    Abstract:

    Unsteady power output and long-term loads (extreme and fatigue) drive wind turbturbine design. However, these loads are difficult to include in optimization loops and are typically only assessed in a post-optimization load analysis or via reduced-order methods. Both alternatives yield suboptimal results. The reason for this difficulty lays in the deterministic approaches to long-term loads assessment. To model the statistics of lifetime loads they require the analysis of many unsteady load cases, generated from many different random seeds—a computationally expensive procedure. In this paper, we present an alternative: a stochastic solution for the unsteady aerodynamic loads based on a projection of the unsteady Blade Element Momentum (BEM) equations onto a stochastic space spanned by chaos exponentials. This approach is similar to the increasingly popular polynomial chaos expansion, but with 2 major differences. First, the BEM equations constitute a random process, varying in time, while previous polynomial chaos expansion methods were concerned with random parameters (ie, random but constant in time or initial values). Second, a new, more efficient basis (the exponential chaos) is used. This new stochastic method enables us to obtain unsteady long-term loads much faster, enabling unsteady loads to become accessible inside wind turbturbine optimization loops. In this paper we derive the stochastic BEM solution and present the most relevant results showing the accuracy of the new method.

  • A fast stochastic solution method for the Blade Element Momentum equations for long‐term load assessment
    Wind Energy, 2017
    Co-Authors: Manuel Fluck, Curran Crawford
    Abstract:

    Unsteady power output and long-term loads (extreme and fatigue) drive wind turbturbine design. However, these loads are difficult to include in optimization loops and are typically only assessed in a post-optimization load analysis or via reduced-order methods. Both alternatives yield suboptimal results. The reason for this difficulty lays in the deterministic approaches to long-term loads assessment. To model the statistics of lifetime loads they require the analysis of many unsteady load cases, generated from many different random seeds—a computationally expensive procedure. In this paper, we present an alternative: a stochastic solution for the unsteady aerodynamic loads based on a projection of the unsteady Blade Element Momentum (BEM) equations onto a stochastic space spanned by chaos exponentials. This approach is similar to the increasingly popular polynomial chaos expansion, but with 2 major differences. First, the BEM equations constitute a random process, varying in time, while previous polynomial chaos expansion methods were concerned with random parameters (ie, random but constant in time or initial values). Second, a new, more efficient basis (the exponential chaos) is used. This new stochastic method enables us to obtain unsteady long-term loads much faster, enabling unsteady loads to become accessible inside wind turbturbine optimization loops. In this paper we derive the stochastic BEM solution and present the most relevant results showing the accuracy of the new method.

  • A Corrected Blade Element Momentum Method for Simulating Wind Turbines in Yawed Flow
    49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2011
    Co-Authors: Michael K. Mcwilliam, Stephen Lawton, Shane Cline, Curran Crawford
    Abstract:

    A new Blade Element Momentum (BEM) model is proposed for yawed wind turbturbine flows. This method differs from conventional methods in the use of correction factors for the induction. A set of results from potential flow methods is used to define a table of corrections over a wide range of operating conditions and locations within the flow field. The potential flow methods account for the distribution of vorticity in the wake. Applying the resulting corrections give better accuracy than conventional BEM methods. By generating the correction results a priori, the efficiency of the BEM method is preserved. The accuracy of this method and the conventional axial Momentum based BEM method are evaluated by comparing results to that of the MEXICO experiment.