Coastal infrastructure, such as bridges and storm surge barriers with weirs, provides an attractive location for harvesting renewable energy using tidal turbines. Often stone layers are applied downstream of coastal infrastructure to protect the sea bed from erosion. However, little is known about the potential effect of tidal energy extraction on the stability of this granular bed protection. This paper describes a study of the flow conditions influencing the stability of the bed protection downstream of a weir-mounted tidal turbine, using hydrodynamic data of an experimental test. The analysis indicates that the flow recirculation zone downstream of a weir may become shorter and flatter due to the presence of a horizontal-axis turbine. As a result, energetic turbulence eddies can transport more horizontal momentum towards the bed – hence the reason a heavier bed protection may be required for granular beds downstream of weirs when a turbine is installed. This information is essential when designing safe bed protections for coastal infrastructure with tidal turbines.
{"title":"Estimating the stability of a bed protection of a weir-mounted tidal turbine","authors":"M. Verbeek, R. Labeur, W. Uijttewaal","doi":"10.36688/IMEJ.3.21-24","DOIUrl":"https://doi.org/10.36688/IMEJ.3.21-24","url":null,"abstract":"Coastal infrastructure, such as bridges and storm surge barriers with weirs, provides an attractive location for harvesting renewable energy using tidal turbines. Often stone layers are applied downstream of coastal infrastructure to protect the sea bed from erosion. However, little is known about the potential effect of tidal energy extraction on the stability of this granular bed protection. This paper describes a study of the flow conditions influencing the stability of the bed protection downstream of a weir-mounted tidal turbine, using hydrodynamic data of an experimental test. The analysis indicates that the flow recirculation zone downstream of a weir may become shorter and flatter due to the presence of a horizontal-axis turbine. As a result, energetic turbulence eddies can transport more horizontal momentum towards the bed – hence the reason a heavier bed protection may be required for granular beds downstream of weirs when a turbine is installed. This information is essential when designing safe bed protections for coastal infrastructure with tidal turbines.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47311303","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A novel wave-energy device is presented. Both a preliminary proof-of-principle of a working, scaled laboratory version of the energy device is shown as well as the derivation and analysis of a comprehensive mathematical and numerical model of the new device. The wave-energy device includes a convergence in which the waves are amplified, a constrained wave buoy with a (curved) mast and direct energy conversion of the buoy motion into electrical power via an electro-magnetic generator. The device is designed for use in breakwaters and it is possible to be taken out of action during severe weather. The new design is a deconstruction of elements of existing wave-energy devices, such as the TapChan, IP wave-buoy and the Berkeley Wedge, put together in a different manner to enhance energy conversion and, hence, efficiency. The idea of wave-focusing in a contraction emerged from our work on creating and simulating rogue waves in crossing seas, including a "bore-soliton-splash". Such crossing seas have been recreated and modelled in the laboratory and in simulations by using a geometric channel convergence. The mathematical and numerical modelling is also novel. One monolithic variational principle governs the dynamics including the combined (potential-flow) hydrodynamics, the buoy motion and the power generation, to which the dissipative elements such as the electrical resistance of the circuits, coils and loads have been added a posteriori. The numerical model is a direct and consistent discretisation of this comprehensive variational principle. Preliminary numerical calculations are shown for the case of linearised dynamics; optimisation of efficiency is a target of future work.
{"title":"A novel wave-energy device with enhanced wave amplification and induction actuator","authors":"O. Bokhove, A. Kalogirou, D. Henry, G. Thomas","doi":"10.36688/IMEJ.3.37-44","DOIUrl":"https://doi.org/10.36688/IMEJ.3.37-44","url":null,"abstract":"A novel wave-energy device is presented. Both a preliminary proof-of-principle of a working, scaled laboratory version of the energy device is shown as well as the derivation and analysis of a comprehensive mathematical and numerical model of the new device. The wave-energy device includes a convergence in which the waves are amplified, a constrained wave buoy with a (curved) mast and direct energy conversion of the buoy motion into electrical power via an electro-magnetic generator. The device is designed for use in breakwaters and it is possible to be taken out of action during severe weather. The new design is a deconstruction of elements of existing wave-energy devices, such as the TapChan, IP wave-buoy and the Berkeley Wedge, put together in a different manner to enhance energy conversion and, hence, efficiency. The idea of wave-focusing in a contraction emerged from our work on creating and simulating rogue waves in crossing seas, including a \"bore-soliton-splash\". Such crossing seas have been recreated and modelled in the laboratory and in simulations by using a geometric channel convergence. The mathematical and numerical modelling is also novel. One monolithic variational principle governs the dynamics including the combined (potential-flow) hydrodynamics, the buoy motion and the power generation, to which the dissipative elements such as the electrical resistance of the circuits, coils and loads have been added a posteriori. The numerical model is a direct and consistent discretisation of this comprehensive variational principle. Preliminary numerical calculations are shown for the case of linearised dynamics; optimisation of efficiency is a target of future work.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47095137","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jonathan M. Whiting, A. Copping, Mikaela C. Freeman, Amy Woodbury
Development of the marine renewable energy (MRE) industry has been challenged by uncertainty about potential environmental effects, which has resulted in slowing of permitting/consenting processes, and ultimately to constraints on the industry. These challenges result from a lack of sufficient devices in the water from which to learn, a dearth of quality monitoring data, and a lack of accessibility to information about these effects in general. This paper describes an ongoing process to improve understanding of the environmental effects of MRE through a public, online knowledge management system developed by the U.S. Department of Energy, known as Tethys (https://tethys.pnnl.gov). Tethys collects and curates relevant documents while supporting a diverse international community through intentional outreach and synthesis activities, many of which support an international collaboration under the IEA Ocean Energy System’s Annex IV. After eight years of operation, Tethys is internationally recognized and viewed as a trusted broker of information, with over 50,000 visitors annually. Tethys has provided clarity around environmental effects during a critical time in the industry when deployments are increasing in size and frequency.
{"title":"Tethys knowledge management system: Working to advance the marine renewable energy industry","authors":"Jonathan M. Whiting, A. Copping, Mikaela C. Freeman, Amy Woodbury","doi":"10.36688/imej.2.29-38","DOIUrl":"https://doi.org/10.36688/imej.2.29-38","url":null,"abstract":"Development of the marine renewable energy (MRE) industry has been challenged by uncertainty about potential environmental effects, which has resulted in slowing of permitting/consenting processes, and ultimately to constraints on the industry. These challenges result from a lack of sufficient devices in the water from which to learn, a dearth of quality monitoring data, and a lack of accessibility to information about these effects in general. This paper describes an ongoing process to improve understanding of the environmental effects of MRE through a public, online knowledge management system developed by the U.S. Department of Energy, known as Tethys (https://tethys.pnnl.gov). Tethys collects and curates relevant documents while supporting a diverse international community through intentional outreach and synthesis activities, many of which support an international collaboration under the IEA Ocean Energy System’s Annex IV. After eight years of operation, Tethys is internationally recognized and viewed as a trusted broker of information, with over 50,000 visitors annually. Tethys has provided clarity around environmental effects during a critical time in the industry when deployments are increasing in size and frequency.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43832653","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Commercial viability of Marine Renewable Energy (MRE) is progressing but no national or international monitoring standards have been established for wave or tidal energy sites. Standardized monitoring within and across MRE sectors is necessary to expedite project permitting/consenting, detect environmental impacts, and enable comparison among sites and technologies. Acoustic backscatter from a bottom-deployed platform at a pilot wave energy site off Newport, Oregon was compared to data collected at a tidal turbine site in Admiralty Inlet, Washington. Metrics that describe fish and macrozooplankton densities and vertical distributions derived from acoustic backscattered energy were compared using wavelets and Autoregressive Moving Average models (ARMA). Average density and vertical distribution values significantly differed between sites. Metrics of density and location in the water column displayed diel (24 h) and tidal (12 h) cycles. Dispersion of animals in the water column varied at 64- and 128-h periods at both sites. Applicability of methods in both sectors suggests that a standard approach to biological monitoring is possible. Stationary acoustics and analytic methods presented here can be used to characterize pre-installation conditions and refine post-installation monitoring to site-specific characteristics to ensure cost-effective detection of impacts associated with MRE development.
{"title":"Does temporal variability limit standardized biological monitoring at wave and tidal energy sites?","authors":"S. Gonzalez, J. Horne, E. Ward","doi":"10.36688/imej.2.15-28","DOIUrl":"https://doi.org/10.36688/imej.2.15-28","url":null,"abstract":"Commercial viability of Marine Renewable Energy (MRE) is progressing but no national or international monitoring standards have been established for wave or tidal energy sites. Standardized monitoring within and across MRE sectors is necessary to expedite project permitting/consenting, detect environmental impacts, and enable comparison among sites and technologies. Acoustic backscatter from a bottom-deployed platform at a pilot wave energy site off Newport, Oregon was compared to data collected at a tidal turbine site in Admiralty Inlet, Washington. Metrics that describe fish and macrozooplankton densities and vertical distributions derived from acoustic backscattered energy were compared using wavelets and Autoregressive Moving Average models (ARMA). Average density and vertical distribution values significantly differed between sites. Metrics of density and location in the water column displayed diel (24 h) and tidal (12 h) cycles. Dispersion of animals in the water column varied at 64- and 128-h periods at both sites. Applicability of methods in both sectors suggests that a standard approach to biological monitoring is possible. Stationary acoustics and analytic methods presented here can be used to characterize pre-installation conditions and refine post-installation monitoring to site-specific characteristics to ensure cost-effective detection of impacts associated with MRE development.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43503661","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The optimisation of a Numerical Wave Tank is proposed to accurately model the sub surface conditions generated by regular waves superimposed on a uniform current velocity. ANSYS CFX 18.0 was used to develop a homogenous multiphase model with volume fractions to define the different phase regions. By applying CFX Expression Language at the inlet of the model, Stokes 2nd Order Theory was used to define the upstream wave and current characteristics. Horizontal and vertical velocity components, as well as surface elevation of the numerical model were compared against theoretical and experimental wave data for 3 different wave characteristics in 2 different water depths. The comparison highlighted the numerical homogeneity between the theoretical and experimental data. Therefore, this study has shown that the modelling procedure used can accurately replicate experimental testing facility flow conditions, providing a potential substitute to experimental flume or tank testing.
{"title":"Development of a wave-current numerical model using Stokes 2nd Order Theory","authors":"Catherine Lloyd, T. O’Doherty, A. Mason-Jones","doi":"10.36688/imej.2.1-14","DOIUrl":"https://doi.org/10.36688/imej.2.1-14","url":null,"abstract":"The optimisation of a Numerical Wave Tank is proposed to accurately model the sub surface conditions generated by regular waves superimposed on a uniform current velocity. ANSYS CFX 18.0 was used to develop a homogenous multiphase model with volume fractions to define the different phase regions. By applying CFX Expression Language at the inlet of the model, Stokes 2nd Order Theory was used to define the upstream wave and current characteristics. Horizontal and vertical velocity components, as well as surface elevation of the numerical model were compared against theoretical and experimental wave data for 3 different wave characteristics in 2 different water depths. The comparison highlighted the numerical homogeneity between the theoretical and experimental data. Therefore, this study has shown that the modelling procedure used can accurately replicate experimental testing facility flow conditions, providing a potential substitute to experimental flume or tank testing.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48245353","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Cross-flow turbines have a number of potential advantages for hydrokinetic energy applications. Two novel control schemes for improving cross-flow turbine energy conversion are introduced and demonstrated through scale experiments. The first aims to alter the local flow conditions on the blades through varying blade kinematics as a function of rotational position, thus increasing beneficial fluid forcing. An established method accomplishes this by oscillating the mounting angle of the blade. Instead we proposed to vary the angular velocity of the blade as a function of azimuthal position. Optimizing this controller resulted in a 59% increase in turbine performance over standard controllers. The second control scheme operates an array of two turbines in a coordinated manner to take advantage of periodic wake structures. For a range of relative turbine positions, a parent controller maintains a constant blade position difference between turbines with the same angular velocity. For select positions, the array efficiency is shown to be greater than that of a single turbine. At the optimal position, coordinated control results in a 4% increase in array performance over uncoordinated operation. Finally, intracycle angular velocity and coordinated control schema are combined.
{"title":"Advanced control methods for cross-flow turbines","authors":"B. Strom, S. Brunton, B. Polagye","doi":"10.36688/IMEJ.1.129-138","DOIUrl":"https://doi.org/10.36688/IMEJ.1.129-138","url":null,"abstract":"Cross-flow turbines have a number of potential advantages for hydrokinetic energy applications. Two novel control schemes for improving cross-flow turbine energy conversion are introduced and demonstrated through scale experiments. The first aims to alter the local flow conditions on the blades through varying blade kinematics as a function of rotational position, thus increasing beneficial fluid forcing. An established method accomplishes this by oscillating the mounting angle of the blade. Instead we proposed to vary the angular velocity of the blade as a function of azimuthal position. Optimizing this controller resulted in a 59% increase in turbine performance over standard controllers. The second control scheme operates an array of two turbines in a coordinated manner to take advantage of periodic wake structures. For a range of relative turbine positions, a parent controller maintains a constant blade position difference between turbines with the same angular velocity. For select positions, the array efficiency is shown to be greater than that of a single turbine. At the optimal position, coordinated control results in a 4% increase in array performance over uncoordinated operation. Finally, intracycle angular velocity and coordinated control schema are combined.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49333353","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
V. Neary, R. Coe, J. Cruz, K. Haas, G. Bacelli, Y. Debruyne, S. Ahn, Victor Nevarez
Classification systems for wave energy resources and wave energy converter (WEC) technologies could provide similar benefits to those for the wind energy industry: resource classification facilitating reconnaissance studies and project planning at both regional and national scales; and WEC classification streamlining and reducing costs of WEC device design and manufacturing. In the present study, a classification system for U.S. wave resources is used to investigate the feasibility of WEC classification. Wave spectra inputs from three wave energy resource classes delineated in this system are used to derive distributions of optimized WEC design scaling factors, as well as WEC design responses. Preliminary results indicate that a single standard WEC design class could serve within a given resource class, and corresponding regional wave climate, due to distinct wave energy distributions and concentrations of energy within partitioned period bands for each resource class. The WEC response to extreme loads was found to vary considerably within the most energetic of the resource classes examined, suggesting the need for these standard design classes to meet structural design requirements based on the upper limits of load response within a given resource class. However, the observed load metric variation is lower than the inter-region resource variations.
{"title":"Classification systems for wave energy resources and WEC technologies","authors":"V. Neary, R. Coe, J. Cruz, K. Haas, G. Bacelli, Y. Debruyne, S. Ahn, Victor Nevarez","doi":"10.36688/IMEJ.1.71-79","DOIUrl":"https://doi.org/10.36688/IMEJ.1.71-79","url":null,"abstract":"Classification systems for wave energy resources and wave energy converter (WEC) technologies could provide similar benefits to those for the wind energy industry: resource classification facilitating reconnaissance studies and project planning at both regional and national scales; and WEC classification streamlining and reducing costs of WEC device design and manufacturing. In the present study, a classification system for U.S. wave resources is used to investigate the feasibility of WEC classification. Wave spectra inputs from three wave energy resource classes delineated in this system are used to derive distributions of optimized WEC design scaling factors, as well as WEC design responses. Preliminary results indicate that a single standard WEC design class could serve within a given resource class, and corresponding regional wave climate, due to distinct wave energy distributions and concentrations of energy within partitioned period bands for each resource class. The WEC response to extreme loads was found to vary considerably within the most energetic of the resource classes examined, suggesting the need for these standard design classes to meet structural design requirements based on the upper limits of load response within a given resource class. However, the observed load metric variation is lower than the inter-region resource variations.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45455426","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper details a hydrodynamic model based on Blade Element Momentum Theory (BEMT) developed to assess ’conventional’ 3-bladed tidal stream turbines (TSTs), adapted here to analyse an ’unconventional’ case of a ducted and open centre device. Validations against a more detailed coupled Reynolds averaged computational fluid dynamics (RANS-BEM) model shows excellent agreement, of within 2% up to the peak power condition, with associated computational times in the order of a few minutes on a single core. The paper demonstrates the application of hydrodynamic forces into a structural analysis tool, in order to assess blade stress distributions of a generic hubless turbine. Incorporation of parameters such as non-uniform inflows and blade weight forces are investigated, with their effects on stress profiles presented. Key findings include: i) the adapted BEMT model replicates the majority of turbine performance characteristics estimated through previous CFD assessments; ii) the proposed model reduces the computational effort by several orders of magnitude compared to the reference coupled CFD, making it suitable for engineering assessments iii) blade stress distribution profiles are quantified, detailing concentration zones and cyclic values for use in fatigue analyses. This work forms part of a greater project aimed to develop a suite of analytical tools to perform engineering assessments of bi-directional ducted TSTs.
{"title":"Adapting conventional tools to analyse ducted and open centre tidal stream turbines","authors":"Steven Allsop, C. Peyrard, P. Bousseau, P. Thies","doi":"10.36688/IMEJ.1.91-99","DOIUrl":"https://doi.org/10.36688/IMEJ.1.91-99","url":null,"abstract":"This paper details a hydrodynamic model based on Blade Element Momentum Theory (BEMT) developed to assess ’conventional’ 3-bladed tidal stream turbines (TSTs), adapted here to analyse an ’unconventional’ case of a ducted and open centre device. Validations against a more detailed coupled Reynolds averaged computational fluid dynamics (RANS-BEM) model shows excellent agreement, of within 2% up to the peak power condition, with associated computational times in the order of a few minutes on a single core. The paper demonstrates the application of hydrodynamic forces into a structural analysis tool, in order to assess blade stress distributions of a generic hubless turbine. Incorporation of parameters such as non-uniform inflows and blade weight forces are investigated, with their effects on stress profiles presented. Key findings include: i) the adapted BEMT model replicates the majority of turbine performance characteristics estimated through previous CFD assessments; ii) the proposed model reduces the computational effort by several orders of magnitude compared to the reference coupled CFD, making it suitable for engineering assessments iii) blade stress distribution profiles are quantified, detailing concentration zones and cyclic values for use in fatigue analyses. This work forms part of a greater project aimed to develop a suite of analytical tools to perform engineering assessments of bi-directional ducted TSTs.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42706305","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Recent research has shown that four-quadrant turbines are required to achieve maximum net energy production in a tidal barrage plant. These turbines can generate electricity in both flow directions and are capable of pumping. An innovative turbine concept is being reviewed in the course of the Eurostars research project Safe*Coast. This project proposes to install a turbine in a reversible cylinder in order to allow for fourquadrant operation. To evaluate the feasibility of the concept, the authors designed a compact low head axial tidal turbine with the aid of CFD simulations. This paper presents the methods used in the design and optimization process of the turbine. It also describes numerically obtained turbine characteristics, and cavitation limits. The most critical requirements of the turbine include high efficiency in turbine and pumping mode and safe cavitation properties. By computing steady state CFD simulations of the turbine stage, an extensive set of geometries was analyzed. The authors optimized the turbine performance by adjusting the meridional section, as well as runner blade and guide vane profiles and angles along with other related parameters. Transient simulations of the whole setup, including the inlet and draft tube geometries, were performed in order to study transient effects. The final design after optimization is a three bladed axial turbine with adjustable guide vanes and a rim generator. The turbine’s symmetrical inlet and outlet geometry and its relative compactness permit its integration in a reversible cylinder. The simulation results are very positive and indicate that all the relevant design criteria are satisfied. As a result, the project will continue into a new phase in which a model of the turbine will be built for physical testing in order to verify the results and to conduct further investigations.
{"title":"Development of a low head tidal turbine","authors":"S. Hötzl, T. Schechtl, P. Rutschmann, W. Knapp","doi":"10.36688/imej.1.81-90","DOIUrl":"https://doi.org/10.36688/imej.1.81-90","url":null,"abstract":"Recent research has shown that four-quadrant turbines are required to achieve maximum net energy production in a tidal barrage plant. These turbines can generate electricity in both flow directions and are capable of pumping. An innovative turbine concept is being reviewed in the course of the Eurostars research project Safe*Coast. This project proposes to install a turbine in a reversible cylinder in order to allow for fourquadrant operation. To evaluate the feasibility of the concept, the authors designed a compact low head axial tidal turbine with the aid of CFD simulations. This paper presents the methods used in the design and optimization process of the turbine. It also describes numerically obtained turbine characteristics, and cavitation limits. The most critical requirements of the turbine include high efficiency in turbine and pumping mode and safe cavitation properties. By computing steady state CFD simulations of the turbine stage, an extensive set of geometries was analyzed. The authors optimized the turbine performance by adjusting the meridional section, as well as runner blade and guide vane profiles and angles along with other related parameters. Transient simulations of the whole setup, including the inlet and draft tube geometries, were performed in order to study transient effects. The final design after optimization is a three bladed axial turbine with adjustable guide vanes and a rim generator. The turbine’s symmetrical inlet and outlet geometry and its relative compactness permit its integration in a reversible cylinder. The simulation results are very positive and indicate that all the relevant design criteria are satisfied. As a result, the project will continue into a new phase in which a model of the turbine will be built for physical testing in order to verify the results and to conduct further investigations.","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43847409","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Actuator line computations of two different tidal turbine rotor designs are presented over a range of tip speed ratios. To account for the reduction in blade loading on the outboard sections of these rotor designs, a spanwise flow correction is applied. This spanwise flow correction is a modified version of the correction factor of Shen et al. (Wind Energy 2005; 8: 457-475) which was originally developed for wind turbine rotors at high tip speed ratios. The modified correction is described as ‘directionally dependent’ in that it allows a more aggressive reduction in the tangential (torque producing) direction than the axial (thrust producing) direction and hence allows the sectional force vector to rotate away from the rotor plane (towards the streamwise direction). When using the modified correction factor, the actuator line computations show a significant improvement in the accuracy of prediction of the rotor thrust and torque, when compared to similar actuator line computations that do not allow the sectional force vector to rotate. Furthermore, the rotation of the sectional force vector is attributed to the changing surface pressure distribution on the outboard sections of the blade, which arises from the spanwise flow along the blade. The rotation of the sectional force vector can also be used to explain the reduction in sectional lift coefficient and increase in sectional drag coefficient that has been observed on the outboard blade sections of several rotors in the literature
在一定的叶尖速比范围内，对两种不同设计的潮汐水轮机转子作动器线进行了计算。考虑到这些转子设计的舷外部分叶片载荷的减少，应用了沿展向的流量校正。该跨向流量校正是Shen等人(Wind Energy 2005;8:457 -475)，最初是为风力涡轮机转子在高尖端速比开发的。修改后的修正被描述为“方向依赖”，因为它允许在切向(产生扭矩)方向上比轴向(产生推力)方向上更积极地减少，因此允许截面力矢量从转子平面旋转(朝着流向方向)。当使用修正修正因子时，与不允许截面力矢量旋转的类似执行器线计算相比，执行器线计算在转子推力和扭矩预测精度方面有显着提高。此外，截面力矢量的旋转归因于叶片外侧截面表面压力分布的变化，这是由沿叶片的展向流动引起的。截面力矢量的旋转也可以用来解释文献中在几个转子的外侧叶片截面上观察到的截面升力系数的减小和截面阻力系数的增加
{"title":"Spanwise flow corrections for tidal turbines","authors":"A. Wimshurst, R. Willden","doi":"10.36688/IMEJ.1.111-121","DOIUrl":"https://doi.org/10.36688/IMEJ.1.111-121","url":null,"abstract":"Actuator line computations of two different tidal turbine rotor designs are presented over a range of tip speed ratios. To account for the reduction in blade loading on the outboard sections of these rotor designs, a spanwise flow correction is applied. This spanwise flow correction is a modified version of the correction factor of Shen et al. (Wind Energy 2005; 8: 457-475) which was originally developed for wind turbine rotors at high tip speed ratios. The modified correction is described as ‘directionally dependent’ in that it allows a more aggressive reduction in the tangential (torque producing) direction than the axial (thrust producing) direction and hence allows the sectional force vector to rotate away from the rotor plane (towards the streamwise direction). When using the modified correction factor, the actuator line computations show a significant improvement in the accuracy of prediction of the rotor thrust and torque, when compared to similar actuator line computations that do not allow the sectional force vector to rotate. Furthermore, the rotation of the sectional force vector is attributed to the changing surface pressure distribution on the outboard sections of the blade, which arises from the spanwise flow along the blade. The rotation of the sectional force vector can also be used to explain the reduction in sectional lift coefficient and increase in sectional drag coefficient that has been observed on the outboard blade sections of several rotors in the literature","PeriodicalId":36111,"journal":{"name":"International Marine Energy Journal","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44195054","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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