Tag Archives: BEM

Shape design and numerical analysis on a 1 MW tidal current turbine for the south-western coast of Korea


Link

Patrick Mark Singh and Young-Do Choi, Renewable Energy – August 2014

Abstract

The study concentrates on the shape design and numerical analysis of a 1 MW horizontal axis tidal current turbine (HATCT), which can be applied near the southwest regions of Korea. On the basis of actual tidal current conditions of south-western region of Korea, configuration design of 1 MW class turbine rotor blade is carried out by blade element momentum theory (BEMT). The hydrodynamic performance including the lift and drag forces, is conducted with the variation of the angle of attack using an open source code of X-Foil. The optimized blade geometry is used for Computational Fluid Dynamics (CFD) analysis with hexahedral numerical grids. This study focuses on developing a new hydrofoil and designing a blade with relatively shorter chord length in contrast to a typical TCT blade. Therefore, after a thorough study of two common hydrofoils, (S814 and DU-91-W2-250, which show good performance for rough conditions), a new hydrofoil, MNU26, is developed. The new hydrofoil has a 26% thickness that can be applied throughout the blade length, giving good structural strength. Power coefficient, pressure and velocity distributions are investigated according to Tip Speed Ratio by CFD analysis. As cavitation analysis is also an important part of the study, it is investigated for all the three hydrofoils. Due to the shorter chord length of the new turbine blade in contrast to a typical TCT blade design, a Fluid Structure Interaction (FSI) analysis is also done. Concrete conclusions have been made after comparing the three hydrofoils, considering their performance, efficiency, occurrence of cavitation and structural feasibility.

Link

Advertisements

Leave a comment

Filed under Component Development, Modeling

A coupled hydro-structural design optimization for hydrokinetic turbines


Nitin Kolekar and Arindam Banerjee – Journal of Renewable and Sustainable Energy, October 2013

Abstract

An optimization methodology for a stall regulated, fixed pitch, horizontal axis hydrokinetic turbine is presented using a combination of a coupled hydro-structural analysis and Genetic Algorithm (GA) based optimization method. Design and analysis is presented for two different designs: a constant chord, zero twist blade, and a variable chord, twisted blade. A hybrid approach is presented combining Blade Element Momentum (BEM), GA, Computational Fluid Dynamics (CFD), and Finite Element Analysis (FEA) techniques. Continue reading

Leave a comment

Filed under Component Development, Modeling

Planning tidal stream turbine array layouts using a coupled blade element momentum – computational fluid dynamics model


Rami Malki, Ian Masters, Alison J. Williams, and T. Nick Croft – Renewable Energy, March 2014

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%.

Link

Leave a comment

Filed under Modeling, System Development

Blade Number Effect for A Horizontal Axis River Current Turbine at A Low Velocity Condition Utilizing A Parametric Study with Mathematical Model of Blade Element Momentum


Ridway Balaka, Aditya Rachman, and Jenny Delly – Journal of Clean Energy Technologies, January 2014

Abstract

The power system using the clean decentralized renewable horizontal axis river current turbine can be an alternative option in delivering locally and sustainably the energies for the communities inaccessible to the electricity connection. One of the important aspects in the technology design is the selection of the blade number. This aspects can raise several consequences including the performance, the manufacturing cost and the construction constrain. The performance must be on the top of the priority in the technology design as the river velocity is typically low which effortlessly brings the technology uneconomically attractive. Continue reading

Leave a comment

Filed under Component Development, Modeling

Quantifying wave and yaw effects on a scale tidal stream turbine


Pascal W. Galloway, Luke E. Myers, and AbuBakr S. Bahaj – Renewable Energy, March 2014

Abstract

The behaviour of Tidal Stream Turbines (TST) in the dynamic flow field caused by waves and rotor misalignment to the incoming flow (yaw) is currently unclear. The dynamic loading applied to the turbine could drive the structural design of the power capture and support subsystems, device size and its proximity to the water surface and sea bed. In addition, the strongly bi-directional nature of the flow encountered at many tidal energy sites may lead to devices omitting yaw drives; accepting the additional dynamic loading associated with rotor misalignment and reduced power production in return for a reduction in device capital cost. Therefore it is imperative to quantify potential unsteady rotor loads so that the TST device design accommodates the inflow conditions and avoids an unacceptable increase in maintenance action or, more seriously, suffers sudden structural failure. Continue reading

Leave a comment

Filed under Component Development, Experiments, Modeling

The influence of flow acceleration on tidal stream turbine wake dynamics: A numerical study using a coupled BEM–CFD model


Ian Masters, Rami Malki, Alison J. Williams, and T. Nicholas Croft – Applied Mathematical Modelling, June 2013

Abstract

Studies of tidal stream turbine performance and of wake development are often conducted in tow-tanks or in regulated flumes with uniform flows across the turbine. Whilst such studies can be very useful, it is questionable as to what extent the results would differ if the flows were more complex in nature, for instance if the flows were unsteady or non-uniform or even both. This study aims to explore whether the results would be affected once we move away from the uniform flow scenario. A numerical modelling study is presented in which tidal stream turbine performance and wake development in non-uniform flow conditions are assessed. The model implements the Blade Element Momentum method for characterising turbine rotor source terms which are used within a computational fluid dynamics model for predicting the interaction between the turbines and the surrounding flow. The model is applied to a rectangular domain and a range of slopes are implemented for the water surface to instigate an increase in flow velocity along the domain. Within an accelerated flow domain wake recovery occurred more rapidly although rotor performance was not affected.

Link

Leave a comment

Filed under Component Development, Modeling

Optimizing the shape of rotor blades for maximum power extraction in marine current turbines


H.R. Karbasian and J.A. Esfahani – International Journal of Automotive and Mechanical Engineering, December, 2012

Abstract

In this paper the shape of rotor blades in Marine Current Turbines (MCTs) are investigated. The evaluation of hydrodynamic loads on blades is performed base on the Blade Element Momentum (BEM) theory. According to main parameters in configurations and operations of these devices the shape of blades are optimized. The optimization is conducted based on the ability of blades to harness the maximum energy during operation conditions. The main parameters investigated here are tip speed ratio and angle of attack. Furthermore, the influence of these considered parameters on the maximum energy extraction from fluid flow over hydrofoil are evaluated. It is shown the effect of angle of attack on power extraction is more than that of tip speed ratio, while both of them are found to be noticeable. Additionally, the proper angle of attack is the angle at which the lift to drag ratio is maximum value. However, if a proper angle of attack is chosen, the variations of power coefficient would not be effectively changed with small variations on tip speed ratio.

Link

Leave a comment

Filed under Modeling

Numerical investigations of the effects of different arrays on power extractions of horizontal axis tidal current turbines


G. Bai, J. Li, P. Fan, and G. Li – Renewable Energy, May 2013

Abstract

As the tidal current industry grows, power extraction from tidal sites has received widespread attention. In this paper, a blade element actuator disk model that is coupled with the blade element method and a three-dimensional Navier–Stokes code is developed to analyse the relationship between power extraction and the layout of turbine arrays. First, a numerical model is constructed to simulate an isolated turbine and the model is validated using experimental data. Then, using this validated model, the power extraction of horizontal axis tidal current turbines using different tidal turbine arrays and rotation directions is predicted. The results of this study demonstrate that staggered grid array turbines can absorb more power from tidal flows than can rectilinear grid array turbines and that staggered grid array turbines are less affected by the rotation of upstream turbines. In addition, for staggered gird arrays, the relationships between power coefficients, lateral distance and longitudinal distance are discussed. The appropriate lateral distance is approximately 2.5 turbine diameters, whereas for the longitudinal distance, the largest value possible should be used. The relative power coefficient can achieve 3.74 when the longitudinal distance is 6 times the turbine diameter. To further increase the power extraction, this study suggests an improved staggered grid array layout. The relative power coefficient of the improved four-row turbine arrays is approximately 3–4% higher than that of the original arrays and will increase as the distance between the second-row and third-row increases. Considering only the first two rows of turbines, the total power extraction can be 11% higher than for an equivalent number of isolated turbines.

Link

Leave a comment

Filed under Modeling

Pitch Angle Effect for Horizontal Axis River Current Turbine


R. Balaka and A. Rachman – Procedia Engineering, 2012

Abstract

The horizontal hydro-kinetic river current turbine power technology is one of the renewable decentralized power services potential in delivering energy for the communities in remote regions inaccessible by electricity connection. The utilization of the kinetic mechanism makes the application of the turbine less environmentally detrimental and more extensively available than the conventional hydro-energy which uses the level differences. However, the only kinetic mechanism of the turbine possibly brings the application to be less economically attractive since the low typical river velocity. This highly possibly results in the low turbine performance. Thus to make the turbine application economically feasible, in the design turbine stage, a preliminary figure on an efficient design is paramount. In order to contribute in satisfying this requirement, this study investigates the effect of the variation of the pitch angle, one of the design turbine parameters, on the horizontal axis river turbine performance. The investigation is conducted by a parametric study with the mathematical model of the Blade Element Momentum theory. The results indicate that the increasing of the pitch angle initially enhances the performance. However, too much pitch angle enhancement results in low performance and reduces the rotation operation which in turn it requires a high gearing ratio of the transmission system. This study also attempts to discuss the philosophy behind the results of the investigation, relating the phenomena to the hydrodynamic behaviour.

Link

Leave a comment

Filed under Modeling