A method to assess the inter-influence between vertical axis, cross-flow turbines in a free stream – 2D numerical modelling (original) (raw)
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In order to determine the optimal arrangement of vertical axis cross-flow marine current turbines within hydropower farms, an innovative, simplified, 2D numerical model was developed. It is based on the interaction between incident flow and turbine blades and was implemented in the CFD software COMSOL Multiphysics. The new approach, which couples a macroscopic model of the main turbine with a RANS calculation, using the k-e turbulence model, proved to save a lot of computational effort. The study pointed on the Achard turbine, a new concept of vertical axis cross-flow turbine. Power coefficients (i.e. turbine efficiency) were calculated for different spatial arrangements of Achard turbines within a hydropower farm. Some trends with respect to the near optimal arrangement could thus be obtained.
Inter-influence of the vertical axis, cross-flow, marine current turbines mounted in farms
In order to determine the optimal arrangement of vertical axis, cross-flow, marine current turbines in hydropower farms, an innovative, simplified, 2D numerical model was developed. It is based on the interaction between incident flow and turbine blades and was implemented in the commercial code COMSOL Multiphysics. The new model proved to save a lot of computational effort. Numerical simulations were performed with the k-\epsilon turbulence model, and turbine power coefficients were calculated for different arrangements. Some trends with respect to the optimal (or near optimal) arrangement could thus be obtained.
In order to determine some optimal (or near optimal) horizontal arrangement of vertical axis cross-flow marine current turbines within hydropower farms, an innovative, simplified, 2D numerical model was developed. It is based on the interaction between incident flow and turbine blades and was implemented in COMSOL Multiphysics. The new approach proved to save a lot of computational effort: it couples a macroscopic non-rotational 2D model of the turbine with a RANS calculation, using the turbulence model in Rotating Machinery, Transient Analysis. The study pointed on the Achard turbine, a new French concept of vertical axis cross-flow turbine. Power coefficients (turbine efficiency) were calculated for different spatial arrangements of Achard turbines within a power farm.
2D NUMERICAL MODELLING OF THE UNSTEADY FLOW IN THE ACHARD TURBINES MOUNTED IN HYDROPOWER FARMS
2000
The present study pointed on the Achard turbine, a new concept of vertical axis cross-flow turbine. In order to determine the optimal arrangement of such marine current turbines within hydropower farms, two different 2D numerical models were implemented in the CFD software COMSOL Multiphysics 3.4, and Fluent 6.3 respectively, using the ε − k turbulence model. Global farm efficiency was
Efficiency of Marine Hydropower Farms Consisting of MultipleVertical Axis Cross-Flow Turbines
This study focuses on the Achard turbine, a vertical axis, cross-flow, marine current turbine module. Similar modules can be superposed to form towers. A marine or river hydropower farm consists of a cluster of barges, each gathering several parallel rows of towers, running in stabilized current. Two-dimensional numerical modelling is performed in a horizontal cross-section of all towers, using FLUENT and COMSOL Multiphysics. Numerical models validation with experimental results is performed through the velocity distribution, depicted by Acoustic Doppler Velocimetry, in the wake of the middle turbine within a farm model. As long as the numerical flow in the wake fits the experiments, the numerical results for the power coefficient (turbine efficiency) are trustworthy. The overall farm efficiency, with respect to the spatial arrangement of the towers, was depicted by 2D modelling of the unsteady flow inside the farm, using COMSOL Multiphysics. Rows of overlapping parallel towers ensu...
This study focuses on the Achard turbine, a French concept of vertical axis, cross-flow, marine current turbine module. The main advantage of such turbines is their modularity: similar modules can be superposed on the same vertical axis, to form towers, with lengths adapted to marine or river current depths, at different locations. A marine or river power farm consists of a cluster of barges, each barge gathering several parallel rows of towers that can be arranged in different configurations. Another advantage of those turbines is their ability to operate irrespective of the water flow direction. The vertical axis cross-flow turbines run in stabilized current, so the flow can be assumed to be almost unchanged in horizontal planes along the vertical z-axis. This assumption allows performing 2D numerical modelling: the computational domain is a cross-section of all towers at a certain z-level. The 2D modelling of the unsteady flow inside such a hydropower farm has been performed using COMSOL Multiphysics, with the ε k turbulence model, to depict the overall efficiency of the farm, with respect to the spatial arrangement of the towers. The efficiency of the turbines increases as the towers get closer to each other, especially on the downstream row.
A innovative modeling approach to investigate the efficiency of cross flow water turbine farms
In 2001, the Geophysical and Industrial Fluid Flows laboratory (LEGI-France) launched the HARVEST research program (Hydroliennes à Axe de Rotation VErtical STabilisé) to better understand and develop a suitable technology for hydroelectric marine or river power farms using Cross Flow Water Turbines (CFWT) piled up in towers. The LEGI researches deal with the hydrodynamic part of these systems, with the support of the R&D Division of the EDF Group; other laboratories of the Rhône-Alpes Region are in charge of the respective mechanical (3S-INPG and LDMS-INSA) and electrical aspects (LEG-INPG). The present study deals with the study of CFWT arrangements. In a first part, a single turbine for free fluid flow conditions is considered. The simulations are carried out with a new in house code which cou- ples a Navier-Stokes computation of the outer flow field with a description of the inner flow field around the turbine. The latter approach is validated with experimental results of a Darri...
Computational Fluid Dynamics Based Optimal Design of Vertical Axis Marine Current Turbines
Marine turbines are being increasingly used to harness kinetic energy of water and convert it into other useful forms of energy. Widespread commercial acceptability of these machines depends upon their efficiency. This largely depends upon the geometric features of the marine turbines such as number of blades, shape of blades etc. Researchers have been using experimental facilities to optimise these machines for maximum power generation. With the advent of advanced computational techniques, it has now become possible to numerically simulate the flow of water in the vicinity of marine turbines and monitor their performance output. In this work Computational Fluid Dynamics (CFD) based techniques have been used to analyse the effects of number of blades within the stator and rotor, of an in-house built Vertical Axis Marine Current Turbine (VAMCT), on the performance output of the turbine. Furthermore, an effort has been put forward towards better understanding of the flow structure in the vicinity of the blades during transient interaction between rotor and stator blades. This study provides vital information with regards to the flow sensors' requirements and placements in order to monitor various blade configurations of a VAMCT in real world. The results of this study show that the torque output from a VAMCT is a strong function of blade configurations and there is a significant degradation in the performance output of marine turbines as the inequality between the number of rotor and stator blades increases. Hence, CFD has the potential to optimise the design of marine turbines and can be used as a potential modelling tool in the near future for on-line health monitoring of such systems.
CFD Analysis for Optimal Single and Double Rows of Marine Turbines in a Wide Channel
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Tidal currents are one of the most promising sources of power within the renewable energy sector, especially for countries with suitable marine conditions. The United Kingdom has the edge over the rest of countries in this type of renewable energy and leads the innovation race in order to keep the UK economy competitive in future years. Following these reasons, several types of marine turbines are currently being developed and tested. Nevertheless, one of the key issues, in the future development of marine hydrokinetic power generation systems, is to properly understand their prospective performance, not only for each power generation device alone but also for an array of devices as a whole. Recent theoretical studies have suggested that a dense cross-stream array of turbines (so-called turbine fence) is a promising way to extract power from marine currents; however, its optimal intra-turbine spacing depends on several physical factors, some of which are still uncertain. One of those uncertain factors is the effect of seabed friction causing vertical shear of the flow, which is difficult to study theoretically and requires 3-D CFD simulations. Also, little is known about the performance of multiple rows of marine turbines. Consequently, throughout this thesis, numerous arrangements of marine turbines (modelled as actuator disks) have been tested using ANSYS Fluent®, with the idea of assessing the effects of various parameters such as: intra-device spacing, number of rows and turbine resistance coefficient. These CFD simulations have been compared with existing theoretical models (two-scale actuator disk models) for the power extracted by the turbines with the aim of validating these theoretical models. Also, the results of CFD simulations have been analysed in detail to better understand the characteristics of flow past these turbine arrays. Keywords: Tidal Turbines, Optimal Spacing, Actuator Disk, RANS Simulations, Open Channel Flow, Marine Energy.
A simple hydropower farm model, equipped with 3 Achard turbine modules, aligned on the same row or put in staggered positions, has been built at 1:5 scale, to be tested in water channel. The 2D numerical modelling of the unsteady flow inside that farm model has been performed with COMSOL Multiphysics, using the k-\epsilon turbulence model, in order to depict the overall efficiency of that farm, with respect to the spatial arrangement of the turbines. Due to the confined flow domain, the efficiency of the studied farm model is obviously greater than the efficiency of a similar farm placed in open current.