China
Africa
Explore chapters and articles related to this topic
Implementing varying blade profile and reynolds number in BEMT code
Published in C. Guedes Soares, Developments in Renewable Energies Offshore, 2020
I. Evans, M. Togneri, T. Lake, R. Gwenter, I. Masters, G. Pinon, M. Slama
Blade Element Momentum Theory (BEMT) is a common tool used in the design and performance evaluation of TST. A robust BEMT model has been developed at Swansea University (Masters et al. 2011, Chapman et al. 2013), which will be the foundation of this work. Previous versions of the BEMT code only allowed for inputs of constant blade profile and Reynolds Number across the radius of the blade. No rotor has a constant blade profile and Reynolds Number across its radius which leads to in-accuracies in the results when using the BEMT model. Implementing inputs of varying blade profile and Reynolds Number across the radius of the blade in the BEMT model will increase the accuracy of the of the blade and hence the results. The BEMT code is also translated and implemented in C++ which should give significant performance gains.
Self-aligning behaviour of a passively yawing floating offshore wind turbine
Published in Ship Technology Research, 2020
Stefan Netzband, Christian W. Schulz, Moustafa Abdel-Maksoud
The number of numerical simulation methods for flow-induced loads and the dynamic behaviour of FOWTs has increased in the past years. Most of them originated by calculating the loads on onshore wind turbines were then modified for the application on offshore wind turbines (OWTs) and now even include hydrodynamic tools to simulate the motion of FOWTs. The methods for turbine simulation are usually based on the blade element momentum theory (BEMT), which is a semi-empirical approach where a rotor blade is cut into several two-dimensional sections. Based on the momentum theory and airfoil coefficients, the forces on each element are calculated and then integrated over the entire rotor. Correction factors are applied to include three-dimensional effects and losses. But since the flow field is not modelled, interactions between the rotor and transient changes in the wake are not considered. A good agreement between simulation results and experimental values have been demonstrated by Laino et al. (2002), among others, for a turbine that is aligned as well as slightly deviated from the main wind direction.
A panel method for floating offshore wind turbine simulations with fully integrated aero- and hydrodynamic modelling in time domain
Published in Ship Technology Research, 2018
Stefan Netzband, Christian W. Schulz, Ulf Göttsche, Daniel Ferreira González, Moustafa Abdel-Maksoud
Accounting for the need of moderate simulation times, state-of-the-art simulation methods use coupled engineering models to estimate the loads on platform and rotor. The blade element momentum theory (BEMT) is commonly used to estimate the aerodynamic loads on the rotor. Based on two-dimensional lift and drag coefficients and the momentum balance in a theoretically assumed stream tube surrounding the rotor, BEMT delivers reasonable results for onshore wind turbine installations under normal operation conditions, as shown, for example, by Laino et al. (2002). The presented simulation results, based on experimentally determined lift and drag coefficients of the S809 aerofoil as well as adjusted coefficients from the Phase VI rotor experiment, show good agreement with measured data from the experiment of the National Renewable Energy Laboratory (NREL) for moderately yawed and non-yawed inflow conditions when the flow is mostly attached. Deep stall, occurring at higher wind speeds in the experiment, can only be modelled utilising the adjusted coefficients with a sufficient accuracy. However, deep stall does not usually occur at modern wind turbine rotors. Therefore, BEMT is suitable for ground-fixed wind turbines, whereas its accuracy for floating turbines is questionable due to the motion of the platform and since the flow field is not modelled explicitly. Owing to the lack of flow field information the blade-wake interaction cannot be taken into account, which further leads to inaccuracies when modelling highly unsteady situations, e.g. fast platform motions or the occurrence of a strong gust because the wake changes its position relative to the blade. Tran and Kim (2015) demonstrated this effect by comparing FAST (BEMT) calculations with RANS calculations of a wind turbine rotor oscillating in the axial direction. For small amplitudes and low oscillation frequencies of the rotor motion, FAST meets the results of the RANS calculations. However, increasing frequency and amplitude to higher – but still realistic – values leads to strong discrepancies between the simulations in thrust and torque. Therefore, the accuracy of BEMT methods is impaired when blade-wake interaction is no longer negligible.